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Merge branch 'master' into filipecaixeta-master

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Alexey Milovidov 2020-10-14 15:27:58 +03:00
commit 87fe8f2a00
670 changed files with 6551 additions and 6148 deletions
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21
base/common/ReplxxLineReader.cpp
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@ -16,19 +16,6 @@ void trim(String & s)
s.erase(std::find_if(s.rbegin(), s.rend(), [](int ch) { return !std::isspace(ch); }).base(), s.end());
}
// Uses separate replxx::Replxx instance to avoid loading them again in the
// current context (replxx::Replxx::history_load() will re-load the history
// from the file), since then they will overlaps with history from the current
// session (this will make behavior compatible with other interpreters, i.e.
// bash).
void history_save(const String & history_file_path, const String & line)
{
replxx::Replxx rx_no_overlap;
rx_no_overlap.history_load(history_file_path);
rx_no_overlap.history_add(line);
rx_no_overlap.history_save(history_file_path);
}
}
ReplxxLineReader::ReplxxLineReader(
@ -58,7 +45,10 @@ ReplxxLineReader::ReplxxLineReader(
}
else
{
rx.history_load(history_file_path);
if (!rx.history_load(history_file_path))
{
rx.print("Loading history failed: %s\n", strerror(errno));
}
if (flock(history_file_fd, LOCK_UN))
{
@ -128,7 +118,8 @@ void ReplxxLineReader::addToHistory(const String & line)
rx.history_add(line);
// flush changes to the disk
history_save(history_file_path, line);
if (!rx.history_save(history_file_path))
rx.print("Saving history failed: %s\n", strerror(errno));
if (locked && 0 != flock(history_file_fd, LOCK_UN))
rx.print("Unlock of history file failed: %s\n", strerror(errno));

2
contrib/replxx vendored

@ -1 +1 @@
Subproject commit 94b1f568d16183214d26c7c0e9ce69a4ce407f65
Subproject commit 8cf626c04e9a74313fb0b474cdbe2297c0f3cdc8

2
docs/en/development/architecture.md
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@ -45,7 +45,7 @@ A `Block` is a container that represents a subset (chunk) of a table in memory.
When we calculate some function over columns in a block, we add another column with its result to the block, and we don’t touch columns for arguments of the function because operations are immutable. Later, unneeded columns can be removed from the block, but not modified. It is convenient for the elimination of common subexpressions.
Blocks are created for every processed chunk of data. Note that for the same type of calculation, the column names and types remain the same for different blocks, and only column data changes. It is better to split block data from the block header because small block sizes have a high overhead of temporary strings for copying shared\_ptrs and column names.
Blocks are created for every processed chunk of data. Note that for the same type of calculation, the column names and types remain the same for different blocks, and only column data changes. It is better to split block data from the block header because small block sizes have a high overhead of temporary strings for copying shared_ptrs and column names.
## Block Streams {#block-streams}

2
docs/en/development/build.md
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@ -7,7 +7,7 @@ toc_title: Build on Linux
Supported platforms:
- x86\_64
- x86_64
- AArch64
- Power9 (experimental)

2
docs/en/development/contrib.md
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@ -26,7 +26,7 @@ toc_title: Third-Party Libraries Used
| libpcg-random | [Apache License 2.0](https://github.com/ClickHouse/ClickHouse/blob/master/contrib/libpcg-random/LICENSE-APACHE.txt) |
| libressl | [OpenSSL License](https://github.com/ClickHouse-Extras/ssl/blob/master/COPYING) |
| librdkafka | [BSD 2-Clause License](https://github.com/edenhill/librdkafka/blob/363dcad5a23dc29381cc626620e68ae418b3af19/LICENSE) |
| libwidechar\_width | [CC0 1.0 Universal](https://github.com/ClickHouse/ClickHouse/blob/master/libs/libwidechar_width/LICENSE) |
| libwidechar_width | [CC0 1.0 Universal](https://github.com/ClickHouse/ClickHouse/blob/master/libs/libwidechar_width/LICENSE) |
| llvm | [BSD 3-Clause License](https://github.com/ClickHouse-Extras/llvm/blob/163def217817c90fb982a6daf384744d8472b92b/llvm/LICENSE.TXT) |
| lz4 | [BSD 2-Clause License](https://github.com/lz4/lz4/blob/c10863b98e1503af90616ae99725ecd120265dfb/LICENSE) |
| mariadb-connector-c | [LGPL v2.1](https://github.com/ClickHouse-Extras/mariadb-connector-c/blob/3.1/COPYING.LIB) |

4
docs/en/development/developer-instruction.md
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@ -40,7 +40,7 @@ In the command line terminal run:
git clone --recursive git@github.com:your_github_username/ClickHouse.git
cd ClickHouse
Note: please, substitute *your\_github\_username* with what is appropriate!
Note: please, substitute *your_github_username* with what is appropriate!
This command will create a directory `ClickHouse` containing the working copy of the project.
@ -150,7 +150,7 @@ Now that you are ready to build ClickHouse we recommend you to create a separate
mkdir build
cd build
You can have several different directories (build\_release, build\_debug, etc.) for different types of build.
You can have several different directories (build_release, build_debug, etc.) for different types of build.
While inside the `build` directory, configure your build by running CMake. Before the first run, you need to define environment variables that specify compiler (version 9 gcc compiler in this example).

6
docs/en/development/style.md
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@ -354,7 +354,7 @@ In all other cases, use a name that describes the meaning.
bool info_successfully_loaded = false;
```
**9.** Names of `define`s and global constants use ALL\_CAPS with underscores.
**9.** Names of `define`s and global constants use ALL_CAPS with underscores.
``` cpp
#define MAX_SRC_TABLE_NAMES_TO_STORE 1000
@ -394,7 +394,7 @@ The underscore suffix can be omitted if the argument is not used in the construc
timer (not m_timer)
```
**14.** For the constants in an `enum`, use CamelCase with a capital letter. ALL\_CAPS is also acceptable. If the `enum` is non-local, use an `enum class`.
**14.** For the constants in an `enum`, use CamelCase with a capital letter. ALL_CAPS is also acceptable. If the `enum` is non-local, use an `enum class`.
``` cpp
enum class CompressionMethod
@ -707,7 +707,7 @@ The standard library is used (`libc++`).
**4.**OS: Linux Ubuntu, not older than Precise.
**5.**Code is written for x86\_64 CPU architecture.
**5.**Code is written for x86_64 CPU architecture.
The CPU instruction set is the minimum supported set among our servers. Currently, it is SSE 4.2.

2
docs/en/development/tests.md
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@ -220,7 +220,7 @@ Debug version of `jemalloc` is used for debug build.
ClickHouse fuzzing is implemented both using [libFuzzer](https://llvm.org/docs/LibFuzzer.html) and random SQL queries.
All the fuzz testing should be performed with sanitizers (Address and Undefined).
LibFuzzer is used for isolated fuzz testing of library code. Fuzzers are implemented as part of test code and have “\_fuzzer” name postfixes.
LibFuzzer is used for isolated fuzz testing of library code. Fuzzers are implemented as part of test code and have “_fuzzer” name postfixes.
Fuzzer example can be found at `src/Parsers/tests/lexer_fuzzer.cpp`. LibFuzzer-specific configs, dictionaries and corpus are stored at `tests/fuzz`.
We encourage you to write fuzz tests for every functionality that handles user input.

12
docs/en/engines/table-engines/integrations/hdfs.md
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@ -71,12 +71,12 @@ Constructions with `{}` are similar to the [remote](../../../sql-reference/table
1. Suppose we have several files in TSV format with the following URIs on HDFS:
- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_1’
- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_2’
- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_3’
- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_1’
- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_2’
- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_3’
- ‘hdfs://hdfs1:9000/some_dir/some_file_1’
- ‘hdfs://hdfs1:9000/some_dir/some_file_2’
- ‘hdfs://hdfs1:9000/some_dir/some_file_3’
- ‘hdfs://hdfs1:9000/another_dir/some_file_1’
- ‘hdfs://hdfs1:9000/another_dir/some_file_2’
- ‘hdfs://hdfs1:9000/another_dir/some_file_3’
1. There are several ways to make a table consisting of all six files:

4
docs/en/engines/table-engines/integrations/kafka.md
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@ -134,7 +134,7 @@ Example:
SELECT level, sum(total) FROM daily GROUP BY level;
```
To improve performance, received messages are grouped into blocks the size of [max\_insert\_block\_size](../../../operations/server-configuration-parameters/settings.md#settings-max_insert_block_size). If the block wasn’t formed within [stream\_flush\_interval\_ms](../../../operations/server-configuration-parameters/settings.md) milliseconds, the data will be flushed to the table regardless of the completeness of the block.
To improve performance, received messages are grouped into blocks the size of [max_insert_block_size](../../../operations/server-configuration-parameters/settings.md#settings-max_insert_block_size). If the block wasn’t formed within [stream_flush_interval_ms](../../../operations/server-configuration-parameters/settings.md) milliseconds, the data will be flushed to the table regardless of the completeness of the block.
To stop receiving topic data or to change the conversion logic, detach the materialized view:
@ -192,6 +192,6 @@ Example:
**See Also**
- [Virtual columns](../../../engines/table-engines/index.md#table_engines-virtual_columns)
- [background\_schedule\_pool\_size](../../../operations/settings/settings.md#background_schedule_pool_size)
- [background_schedule_pool_size](../../../operations/settings/settings.md#background_schedule_pool_size)
[Original article](https://clickhouse.tech/docs/en/operations/table_engines/kafka/) <!--hide-->

2
docs/en/engines/table-engines/integrations/rabbitmq.md
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@ -109,7 +109,7 @@ Setting `rabbitmq_queue_base` may be used for the following cases:
- to be able to restore reading from certain durable queues when not all messages were successfully consumed. To resume consumption from one specific queue - set its name in `rabbitmq_queue_base` setting and do not specify `rabbitmq_num_consumers` and `rabbitmq_num_queues` (defaults to 1). To resume consumption from all queues, which were declared for a specific table - just specify the same settings: `rabbitmq_queue_base`, `rabbitmq_num_consumers`, `rabbitmq_num_queues`. By default, queue names will be unique to tables.
- to reuse queues as they are declared durable and not auto-deleted. (Can be deleted via any of RabbitMQ CLI tools.)
To improve performance, received messages are grouped into blocks the size of [max\_insert\_block\_size](../../../operations/server-configuration-parameters/settings.md#settings-max_insert_block_size). If the block wasn’t formed within [stream\_flush\_interval\_ms](../../../operations/server-configuration-parameters/settings.md) milliseconds, the data will be flushed to the table regardless of the completeness of the block.
To improve performance, received messages are grouped into blocks the size of [max_insert_block_size](../../../operations/server-configuration-parameters/settings.md#settings-max_insert_block_size). If the block wasn’t formed within [stream_flush_interval_ms](../../../operations/server-configuration-parameters/settings.md) milliseconds, the data will be flushed to the table regardless of the completeness of the block.
If `rabbitmq_num_consumers` and/or `rabbitmq_num_queues` settings are specified along with `rabbitmq_exchange_type`, then:

2
docs/en/engines/table-engines/mergetree-family/custom-partitioning-key.md
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@ -114,7 +114,7 @@ drwxr-xr-x 2 clickhouse clickhouse 4096 Feb 5 12:09 201902_4_6_1
drwxr-xr-x 2 clickhouse clickhouse 4096 Feb 1 16:48 detached
```
The folders ‘201901\_1\_1\_0’, ‘201901\_1\_7\_1’ and so on are the directories of the parts. Each part relates to a corresponding partition and contains data just for a certain month (the table in this example has partitioning by month).
The folders ‘201901_1_1_0’, ‘201901_1_7_1’ and so on are the directories of the parts. Each part relates to a corresponding partition and contains data just for a certain month (the table in this example has partitioning by month).
The `detached` directory contains parts that were detached from the table using the [DETACH](../../../sql-reference/statements/alter/partition.md#alter_detach-partition) query. The corrupted parts are also moved to this directory, instead of being deleted. The server does not use the parts from the `detached` directory. You can add, delete, or modify the data in this directory at any time – the server will not know about this until you run the [ATTACH](../../../sql-reference/statements/alter/partition.md#alter_attach-partition) query.

2
docs/en/engines/table-engines/mergetree-family/graphitemergetree.md
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@ -79,7 +79,7 @@ All of the parameters excepting `config_section` have the same meaning as in `Me
## Rollup Configuration {#rollup-configuration}
The settings for rollup are defined by the [graphite\_rollup](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-graphite) parameter in the server configuration. The name of the parameter could be any. You can create several configurations and use them for different tables.
The settings for rollup are defined by the [graphite_rollup](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-graphite) parameter in the server configuration. The name of the parameter could be any. You can create several configurations and use them for different tables.
Rollup configuration structure:

12
docs/en/engines/table-engines/mergetree-family/mergetree.md
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@ -205,7 +205,7 @@ The number of columns in the primary key is not explicitly limited. Depending on
A long primary key will negatively affect the insert performance and memory consumption, but extra columns in the primary key do not affect ClickHouse performance during `SELECT` queries.
You can create a table without a primary key using the `ORDER BY tuple()` syntax. In this case, ClickHouse stores data in the order of inserting. If you want to save data order when inserting data by `INSERT ... SELECT` queries, set [max\_insert\_threads = 1](../../../operations/settings/settings.md#settings-max-insert-threads).
You can create a table without a primary key using the `ORDER BY tuple()` syntax. In this case, ClickHouse stores data in the order of inserting. If you want to save data order when inserting data by `INSERT ... SELECT` queries, set [max_insert_threads = 1](../../../operations/settings/settings.md#settings-max-insert-threads).
To select data in the initial order, use [single-threaded](../../../operations/settings/settings.md#settings-max_threads) `SELECT` queries.
@ -248,7 +248,7 @@ In the example below, the index can’t be used.
SELECT count() FROM table WHERE CounterID = 34 OR URL LIKE '%upyachka%'
```
To check whether ClickHouse can use the index when running a query, use the settings [force\_index\_by\_date](../../../operations/settings/settings.md#settings-force_index_by_date) and [force\_primary\_key](../../../operations/settings/settings.md).
To check whether ClickHouse can use the index when running a query, use the settings [force_index_by_date](../../../operations/settings/settings.md#settings-force_index_by_date) and [force_primary_key](../../../operations/settings/settings.md).
The key for partitioning by month allows reading only those data blocks which contain dates from the proper range. In this case, the data block may contain data for many dates (up to an entire month). Within a block, data is sorted by primary key, which might not contain the date as the first column. Because of this, using a query with only a date condition that does not specify the primary key prefix will cause more data to be read than for a single date.
@ -339,7 +339,7 @@ Conditions in the `WHERE` clause contains calls of the functions that operate wi
The `set` index can be used with all functions. Function subsets for other indexes are shown in the table below.
| Function (operator) / Index | primary key | minmax | ngrambf\_v1 | tokenbf\_v1 | bloom\_filter |
| Function (operator) / Index | primary key | minmax | ngrambf_v1 | tokenbf_v1 | bloom_filter |
|------------------------------------------------------------------------------------------------------------|-------------|--------|-------------|-------------|---------------|
| [equals (=, ==)](../../../sql-reference/functions/comparison-functions.md#function-equals) | ✔ | ✔ | ✔ | ✔ | ✔ |
| [notEquals(!=, \<\>)](../../../sql-reference/functions/comparison-functions.md#function-notequals) | ✔ | ✔ | ✔ | ✔ | ✔ |
@ -505,7 +505,7 @@ Data part is the minimum movable unit for `MergeTree`-engine tables. The data be
- Volume — Ordered set of equal disks (similar to [JBOD](https://en.wikipedia.org/wiki/Non-RAID_drive_architectures)).
- Storage policy — Set of volumes and the rules for moving data between them.
The names given to the described entities can be found in the system tables, [system.storage\_policies](../../../operations/system-tables/storage_policies.md#system_tables-storage_policies) and [system.disks](../../../operations/system-tables/disks.md#system_tables-disks). To apply one of the configured storage policies for a table, use the `storage_policy` setting of `MergeTree`-engine family tables.
The names given to the described entities can be found in the system tables, [system.storage_policies](../../../operations/system-tables/storage_policies.md#system_tables-storage_policies) and [system.disks](../../../operations/system-tables/disks.md#system_tables-disks). To apply one of the configured storage policies for a table, use the `storage_policy` setting of `MergeTree`-engine family tables.
### Configuration {#table_engine-mergetree-multiple-volumes_configure}
@ -635,7 +635,7 @@ SETTINGS storage_policy = 'moving_from_ssd_to_hdd'
The `default` storage policy implies using only one volume, which consists of only one disk given in `<path>`. Once a table is created, its storage policy cannot be changed.
The number of threads performing background moves of data parts can be changed by [background\_move\_pool\_size](../../../operations/settings/settings.md#background_move_pool_size) setting.
The number of threads performing background moves of data parts can be changed by [background_move_pool_size](../../../operations/settings/settings.md#background_move_pool_size) setting.
### Details {#details}
@ -654,7 +654,7 @@ In all these cases except for mutations and partition freezing, a part is stored
Under the hood, mutations and partition freezing make use of [hard links](https://en.wikipedia.org/wiki/Hard_link). Hard links between different disks are not supported, therefore in such cases the resulting parts are stored on the same disks as the initial ones.
In the background, parts are moved between volumes on the basis of the amount of free space (`move_factor` parameter) according to the order the volumes are declared in the configuration file.
Data is never transferred from the last one and into the first one. One may use system tables [system.part\_log](../../../operations/system-tables/part_log.md#system_tables-part-log) (field `type = MOVE_PART`) and [system.parts](../../../operations/system-tables/parts.md#system_tables-parts) (fields `path` and `disk`) to monitor background moves. Also, the detailed information can be found in server logs.
Data is never transferred from the last one and into the first one. One may use system tables [system.part_log](../../../operations/system-tables/part_log.md#system_tables-part-log) (field `type = MOVE_PART`) and [system.parts](../../../operations/system-tables/parts.md#system_tables-parts) (fields `path` and `disk`) to monitor background moves. Also, the detailed information can be found in server logs.
User can force moving a part or a partition from one volume to another using the query [ALTER TABLE … MOVE PART\|PARTITION … TO VOLUME\|DISK …](../../../sql-reference/statements/alter/partition.md#alter_move-partition), all the restrictions for background operations are taken into account. The query initiates a move on its own and does not wait for background operations to be completed. User will get an error message if not enough free space is available or if any of the required conditions are not met.

8
docs/en/engines/table-engines/mergetree-family/replication.md
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@ -57,19 +57,19 @@ You can specify any existing ZooKeeper cluster and the system will use a directo
If ZooKeeper isn’t set in the config file, you can’t create replicated tables, and any existing replicated tables will be read-only.
ZooKeeper is not used in `SELECT` queries because replication does not affect the performance of `SELECT` and queries run just as fast as they do for non-replicated tables. When querying distributed replicated tables, ClickHouse behavior is controlled by the settings [max\_replica\_delay\_for\_distributed\_queries](../../../operations/settings/settings.md#settings-max_replica_delay_for_distributed_queries) and [fallback\_to\_stale\_replicas\_for\_distributed\_queries](../../../operations/settings/settings.md#settings-fallback_to_stale_replicas_for_distributed_queries).
ZooKeeper is not used in `SELECT` queries because replication does not affect the performance of `SELECT` and queries run just as fast as they do for non-replicated tables. When querying distributed replicated tables, ClickHouse behavior is controlled by the settings [max_replica_delay_for_distributed_queries](../../../operations/settings/settings.md#settings-max_replica_delay_for_distributed_queries) and [fallback_to_stale_replicas_for_distributed_queries](../../../operations/settings/settings.md#settings-fallback_to_stale_replicas_for_distributed_queries).
For each `INSERT` query, approximately ten entries are added to ZooKeeper through several transactions. (To be more precise, this is for each inserted block of data; an INSERT query contains one block or one block per `max_insert_block_size = 1048576` rows.) This leads to slightly longer latencies for `INSERT` compared to non-replicated tables. But if you follow the recommendations to insert data in batches of no more than one `INSERT` per second, it doesn’t create any problems. The entire ClickHouse cluster used for coordinating one ZooKeeper cluster has a total of several hundred `INSERTs` per second. The throughput on data inserts (the number of rows per second) is just as high as for non-replicated data.
For very large clusters, you can use different ZooKeeper clusters for different shards. However, this hasn’t proven necessary on the Yandex.Metrica cluster (approximately 300 servers).
Replication is asynchronous and multi-master. `INSERT` queries (as well as `ALTER`) can be sent to any available server. Data is inserted on the server where the query is run, and then it is copied to the other servers. Because it is asynchronous, recently inserted data appears on the other replicas with some latency. If part of the replicas are not available, the data is written when they become available. If a replica is available, the latency is the amount of time it takes to transfer the block of compressed data over the network. The number of threads performing background tasks for replicated tables can be set by [background\_schedule\_pool\_size](../../../operations/settings/settings.md#background_schedule_pool_size) setting.
Replication is asynchronous and multi-master. `INSERT` queries (as well as `ALTER`) can be sent to any available server. Data is inserted on the server where the query is run, and then it is copied to the other servers. Because it is asynchronous, recently inserted data appears on the other replicas with some latency. If part of the replicas are not available, the data is written when they become available. If a replica is available, the latency is the amount of time it takes to transfer the block of compressed data over the network. The number of threads performing background tasks for replicated tables can be set by [background_schedule_pool_size](../../../operations/settings/settings.md#background_schedule_pool_size) setting.
By default, an INSERT query waits for confirmation of writing the data from only one replica. If the data was successfully written to only one replica and the server with this replica ceases to exist, the stored data will be lost. To enable getting confirmation of data writes from multiple replicas, use the `insert_quorum` option.
Each block of data is written atomically. The INSERT query is divided into blocks up to `max_insert_block_size = 1048576` rows. In other words, if the `INSERT` query has less than 1048576 rows, it is made atomically.
Data blocks are deduplicated. For multiple writes of the same data block (data blocks of the same size containing the same rows in the same order), the block is only written once. The reason for this is in case of network failures when the client application doesn’t know if the data was written to the DB, so the `INSERT` query can simply be repeated. It doesn’t matter which replica INSERTs were sent to with identical data. `INSERTs` are idempotent. Deduplication parameters are controlled by [merge\_tree](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-merge_tree) server settings.
Data blocks are deduplicated. For multiple writes of the same data block (data blocks of the same size containing the same rows in the same order), the block is only written once. The reason for this is in case of network failures when the client application doesn’t know if the data was written to the DB, so the `INSERT` query can simply be repeated. It doesn’t matter which replica INSERTs were sent to with identical data. `INSERTs` are idempotent. Deduplication parameters are controlled by [merge_tree](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-merge_tree) server settings.
During replication, only the source data to insert is transferred over the network. Further data transformation (merging) is coordinated and performed on all the replicas in the same way. This minimizes network usage, which means that replication works well when replicas reside in different datacenters. (Note that duplicating data in different datacenters is the main goal of replication.)
@ -217,6 +217,6 @@ If the data in ZooKeeper was lost or damaged, you can save data by moving it to
**See also**
- [background\_schedule\_pool\_size](../../../operations/settings/settings.md#background_schedule_pool_size)
- [background_schedule_pool_size](../../../operations/settings/settings.md#background_schedule_pool_size)
[Original article](https://clickhouse.tech/docs/en/operations/table_engines/replication/) <!--hide-->

10
docs/en/engines/table-engines/special/distributed.md
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@ -97,13 +97,13 @@ Cluster names must not contain dots.
The parameters `host`, `port`, and optionally `user`, `password`, `secure`, `compression` are specified for each server:
- `host` – The address of the remote server. You can use either the domain or the IPv4 or IPv6 address. If you specify the domain, the server makes a DNS request when it starts, and the result is stored as long as the server is running. If the DNS request fails, the server doesn’t start. If you change the DNS record, restart the server.
- `port` – The TCP port for messenger activity (`tcp_port` in the config, usually set to 9000). Do not confuse it with http\_port.
- `port` – The TCP port for messenger activity (`tcp_port` in the config, usually set to 9000). Do not confuse it with http_port.
- `user` – Name of the user for connecting to a remote server. Default value: default. This user must have access to connect to the specified server. Access is configured in the users.xml file. For more information, see the section [Access rights](../../../operations/access-rights.md).
- `password` – The password for connecting to a remote server (not masked). Default value: empty string.
- `secure` - Use ssl for connection, usually you also should define `port` = 9440. Server should listen on `<tcp_port_secure>9440</tcp_port_secure>` and have correct certificates.
- `compression` - Use data compression. Default value: true.
When specifying replicas, one of the available replicas will be selected for each of the shards when reading. You can configure the algorithm for load balancing (the preference for which replica to access) – see the [load\_balancing](../../../operations/settings/settings.md#settings-load_balancing) setting.
When specifying replicas, one of the available replicas will be selected for each of the shards when reading. You can configure the algorithm for load balancing (the preference for which replica to access) – see the [load_balancing](../../../operations/settings/settings.md#settings-load_balancing) setting.
If the connection with the server is not established, there will be an attempt to connect with a short timeout. If the connection failed, the next replica will be selected, and so on for all the replicas. If the connection attempt failed for all the replicas, the attempt will be repeated the same way, several times.
This works in favour of resiliency, but does not provide complete fault tolerance: a remote server might accept the connection, but might not work, or work poorly.
@ -144,11 +144,11 @@ You should be concerned about the sharding scheme in the following cases:
- Queries are used that require joining data (IN or JOIN) by a specific key. If data is sharded by this key, you can use local IN or JOIN instead of GLOBAL IN or GLOBAL JOIN, which is much more efficient.
- A large number of servers is used (hundreds or more) with a large number of small queries (queries of individual clients - websites, advertisers, or partners). In order for the small queries to not affect the entire cluster, it makes sense to locate data for a single client on a single shard. Alternatively, as we’ve done in Yandex.Metrica, you can set up bi-level sharding: divide the entire cluster into “layers”, where a layer may consist of multiple shards. Data for a single client is located on a single layer, but shards can be added to a layer as necessary, and data is randomly distributed within them. Distributed tables are created for each layer, and a single shared distributed table is created for global queries.
Data is written asynchronously. When inserted in the table, the data block is just written to the local file system. The data is sent to the remote servers in the background as soon as possible. The period for sending data is managed by the [distributed\_directory\_monitor\_sleep\_time\_ms](../../../operations/settings/settings.md#distributed_directory_monitor_sleep_time_ms) and [distributed\_directory\_monitor\_max\_sleep\_time\_ms](../../../operations/settings/settings.md#distributed_directory_monitor_max_sleep_time_ms) settings. The `Distributed` engine sends each file with inserted data separately, but you can enable batch sending of files with the [distributed\_directory\_monitor\_batch\_inserts](../../../operations/settings/settings.md#distributed_directory_monitor_batch_inserts) setting. This setting improves cluster performance by better utilizing local server and network resources. You should check whether data is sent successfully by checking the list of files (data waiting to be sent) in the table directory: `/var/lib/clickhouse/data/database/table/`. The number of threads performing background tasks can be set by [background\_distributed\_schedule\_pool\_size](../../../operations/settings/settings.md#background_distributed_schedule_pool_size) setting.
Data is written asynchronously. When inserted in the table, the data block is just written to the local file system. The data is sent to the remote servers in the background as soon as possible. The period for sending data is managed by the [distributed_directory_monitor_sleep_time_ms](../../../operations/settings/settings.md#distributed_directory_monitor_sleep_time_ms) and [distributed_directory_monitor_max_sleep_time_ms](../../../operations/settings/settings.md#distributed_directory_monitor_max_sleep_time_ms) settings. The `Distributed` engine sends each file with inserted data separately, but you can enable batch sending of files with the [distributed_directory_monitor_batch_inserts](../../../operations/settings/settings.md#distributed_directory_monitor_batch_inserts) setting. This setting improves cluster performance by better utilizing local server and network resources. You should check whether data is sent successfully by checking the list of files (data waiting to be sent) in the table directory: `/var/lib/clickhouse/data/database/table/`. The number of threads performing background tasks can be set by [background_distributed_schedule_pool_size](../../../operations/settings/settings.md#background_distributed_schedule_pool_size) setting.
If the server ceased to exist or had a rough restart (for example, after a device failure) after an INSERT to a Distributed table, the inserted data might be lost. If a damaged data part is detected in the table directory, it is transferred to the `broken` subdirectory and no longer used.
When the `max_parallel_replicas` option is enabled, query processing is parallelized across all replicas within a single shard. For more information, see the section [max\_parallel\_replicas](../../../operations/settings/settings.md#settings-max_parallel_replicas).
When the `max_parallel_replicas` option is enabled, query processing is parallelized across all replicas within a single shard. For more information, see the section [max_parallel_replicas](../../../operations/settings/settings.md#settings-max_parallel_replicas).
## Virtual Columns {#virtual-columns}
@ -160,6 +160,6 @@ When the `max_parallel_replicas` option is enabled, query processing is parallel
**See Also**
- [Virtual columns](../../../engines/table-engines/special/index.md#table_engines-virtual_columns)
- [background\_distributed\_schedule\_pool\_size](../../../operations/settings/settings.md#background_distributed_schedule_pool_size)
- [background_distributed_schedule_pool_size](../../../operations/settings/settings.md#background_distributed_schedule_pool_size)
[Original article](https://clickhouse.tech/docs/en/operations/table_engines/distributed/) <!--hide-->

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@ -25,10 +25,10 @@ You may have multiple sections like this, for the number of tables being transmi
**–file** – Path to the file with the table dump, or -, which refers to stdin.
Only a single table can be retrieved from stdin.
The following parameters are optional: **–name**– Name of the table. If omitted, \_data is used.
The following parameters are optional: **–name**– Name of the table. If omitted, _data is used.
**–format** – Data format in the file. If omitted, TabSeparated is used.
One of the following parameters is required:**–types** – A list of comma-separated column types. For example: `UInt64,String`. The columns will be named \_1, \_2, …
One of the following parameters is required:**–types** – A list of comma-separated column types. For example: `UInt64,String`. The columns will be named _1, _2, …
**–structure**– The table structure in the format`UserID UInt64`, `URL String`. Defines the column names and types.
The files specified in ‘file’ will be parsed by the format specified in ‘format’, using the data types specified in ‘types’ or ‘structure’. The table will be uploaded to the server and accessible there as a temporary table with the name in ‘name’.

12
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@ -93,15 +93,15 @@ You cannot perform a `SELECT` query directly from the table. Instead, use one of
When creating a table, the following settings are applied:
- [join\_use\_nulls](../../../operations/settings/settings.md#join_use_nulls)
- [max\_rows\_in\_join](../../../operations/settings/query-complexity.md#settings-max_rows_in_join)
- [max\_bytes\_in\_join](../../../operations/settings/query-complexity.md#settings-max_bytes_in_join)
- [join\_overflow\_mode](../../../operations/settings/query-complexity.md#settings-join_overflow_mode)
- [join\_any\_take\_last\_row](../../../operations/settings/settings.md#settings-join_any_take_last_row)
- [join_use_nulls](../../../operations/settings/settings.md#join_use_nulls)
- [max_rows_in_join](../../../operations/settings/query-complexity.md#settings-max_rows_in_join)
- [max_bytes_in_join](../../../operations/settings/query-complexity.md#settings-max_bytes_in_join)
- [join_overflow_mode](../../../operations/settings/query-complexity.md#settings-join_overflow_mode)
- [join_any_take_last_row](../../../operations/settings/settings.md#settings-join_any_take_last_row)
The `Join`-engine tables can’t be used in `GLOBAL JOIN` operations.
The `Join`-engine allows use [join\_use\_nulls](../../../operations/settings/settings.md#join_use_nulls) setting in the `CREATE TABLE` statement. And [SELECT](../../../sql-reference/statements/select/index.md) query allows use `join_use_nulls` too. If you have different `join_use_nulls` settings, you can get an error joining table. It depends on kind of JOIN. When you use [joinGet](../../../sql-reference/functions/other-functions.md#joinget) function, you have to use the same `join_use_nulls` setting in `CRATE TABLE` and `SELECT` statements.
The `Join`-engine allows use [join_use_nulls](../../../operations/settings/settings.md#join_use_nulls) setting in the `CREATE TABLE` statement. And [SELECT](../../../sql-reference/statements/select/index.md) query allows use `join_use_nulls` too. If you have different `join_use_nulls` settings, you can get an error joining table. It depends on kind of JOIN. When you use [joinGet](../../../sql-reference/functions/other-functions.md#joinget) function, you have to use the same `join_use_nulls` setting in `CRATE TABLE` and `SELECT` statements.
## Data Storage {#data-storage}

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@ -33,7 +33,7 @@ The typical way to use the `Merge` engine is for working with a large number of
Example 2:
Let’s say you have a old table (WatchLog\_old) and decided to change partitioning without moving data to a new table (WatchLog\_new) and you need to see data from both tables.
Let’s say you have a old table (WatchLog_old) and decided to change partitioning without moving data to a new table (WatchLog_new) and you need to see data from both tables.
``` sql
CREATE TABLE WatchLog_old(date Date, UserId Int64, EventType String, Cnt UInt64)

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@ -23,7 +23,7 @@ additional headers for getting a response from the server.
respectively. For processing `POST` requests, the remote server must support
[Chunked transfer encoding](https://en.wikipedia.org/wiki/Chunked_transfer_encoding).
You can limit the maximum number of HTTP GET redirect hops using the [max\_http\_get\_redirects](../../../operations/settings/settings.md#setting-max_http_get_redirects) setting.
You can limit the maximum number of HTTP GET redirect hops using the [max_http_get_redirects](../../../operations/settings/settings.md#setting-max_http_get_redirects) setting.
## Example {#example}

2
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@ -40,7 +40,7 @@ Question candidates:
- How to implement pivot (like in pandas)?
- How to remove the default ClickHouse user through users.d?
- Importing MySQL dump to Clickhouse
- Window function workarounds (row\_number, lag/lead, running diff/sum/average)
- Window function workarounds (row_number, lag/lead, running diff/sum/average)
##}
{## [Original article](https://clickhouse.tech/docs/en/faq) ##}

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@ -6,7 +6,7 @@ toc_priority: 20
# What If I Have a Problem with Encodings When Using Oracle Via ODBC? {#oracle-odbc-encodings}
If you use Oracle as a source of ClickHouse external dictionaries via Oracle ODBC driver, you need to set the correct value for the `NLS_LANG` environment variable in `/etc/default/clickhouse`. For more information, see the [Oracle NLS\_LANG FAQ](https://www.oracle.com/technetwork/products/globalization/nls-lang-099431.html).
If you use Oracle as a source of ClickHouse external dictionaries via Oracle ODBC driver, you need to set the correct value for the `NLS_LANG` environment variable in `/etc/default/clickhouse`. For more information, see the [Oracle NLS_LANG FAQ](https://www.oracle.com/technetwork/products/globalization/nls-lang-099431.html).
**Example**

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@ -7,7 +7,7 @@ toc_title: AMPLab Big Data Benchmark
See https://amplab.cs.berkeley.edu/benchmark/
Sign up for a free account at https://aws.amazon.com. It requires a credit card, email, and phone number. Get a new access key at https://console.aws.amazon.com/iam/home?nc2=h\_m\_sc\#security\_credential
Sign up for a free account at https://aws.amazon.com. It requires a credit card, email, and phone number. Get a new access key at https://console.aws.amazon.com/iam/home?nc2=h_m_sc#security_credential
Run the following in the console:

2
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@ -195,7 +195,7 @@ The data in this table uses 142 GB.
(Importing data directly from Postgres is also possible using `COPY ... TO PROGRAM`.)
Unfortunately, all the fields associated with the weather (precipitation…average\_wind\_speed) were filled with NULL. Because of this, we will remove them from the final data set.
Unfortunately, all the fields associated with the weather (precipitation…average_wind_speed) were filled with NULL. Because of this, we will remove them from the final data set.
To start, we’ll create a table on a single server. Later we will make the table distributed.

4
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@ -7,9 +7,9 @@ toc_title: Installation
## System Requirements {#system-requirements}
ClickHouse can run on any Linux, FreeBSD, or Mac OS X with x86\_64, AArch64, or PowerPC64LE CPU architecture.
ClickHouse can run on any Linux, FreeBSD, or Mac OS X with x86_64, AArch64, or PowerPC64LE CPU architecture.
Official pre-built binaries are typically compiled for x86\_64 and leverage SSE 4.2 instruction set, so unless otherwise stated usage of CPU that supports it becomes an additional system requirement. Here’s the command to check if current CPU has support for SSE 4.2:
Official pre-built binaries are typically compiled for x86_64 and leverage SSE 4.2 instruction set, so unless otherwise stated usage of CPU that supports it becomes an additional system requirement. Here’s the command to check if current CPU has support for SSE 4.2:
``` bash
$ grep -q sse4_2 /proc/cpuinfo && echo "SSE 4.2 supported" || echo "SSE 4.2 not supported"

8
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@ -38,10 +38,10 @@ The queries are executed as a read-only user. It implies some limitations:
The following settings are also enforced:
- [max\_result\_bytes=10485760](../operations/settings/query_complexity/#max-result-bytes)
- [max\_result\_rows=2000](../operations/settings/query_complexity/#setting-max_result_rows)
- [result\_overflow\_mode=break](../operations/settings/query_complexity/#result-overflow-mode)
- [max\_execution\_time=60000](../operations/settings/query_complexity/#max-execution-time)
- [max_result_bytes=10485760](../operations/settings/query_complexity/#max-result-bytes)
- [max_result_rows=2000](../operations/settings/query_complexity/#setting-max_result_rows)
- [result_overflow_mode=break](../operations/settings/query_complexity/#result-overflow-mode)
- [max_execution_time=60000](../operations/settings/query_complexity/#max-execution-time)
## Examples {#examples}

10
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@ -11,10 +11,10 @@ In a “normal” row-oriented DBMS, data is stored in this order:
| Row | WatchID | JavaEnable | Title | GoodEvent | EventTime |
|-----|-------------|------------|--------------------|-----------|---------------------|
| \#0 | 89354350662 | 1 | Investor Relations | 1 | 2016-05-18 05:19:20 |
| \#1 | 90329509958 | 0 | Contact us | 1 | 2016-05-18 08:10:20 |
| \#2 | 89953706054 | 1 | Mission | 1 | 2016-05-18 07:38:00 |
| \#N | … | … | … | … | … |
| #0 | 89354350662 | 1 | Investor Relations | 1 | 2016-05-18 05:19:20 |
| #1 | 90329509958 | 0 | Contact us | 1 | 2016-05-18 08:10:20 |
| #2 | 89953706054 | 1 | Mission | 1 | 2016-05-18 07:38:00 |
| #N | … | … | … | … | … |
In other words, all the values related to a row are physically stored next to each other.
@ -22,7 +22,7 @@ Examples of a row-oriented DBMS are MySQL, Postgres, and MS SQL Server.
In a column-oriented DBMS, data is stored like this:
| Row: | \#0 | \#1 | \#2 | \#N |
| Row: | #0 | #1 | #2 | #N |
|-------------|---------------------|---------------------|---------------------|-----|
| WatchID: | 89354350662 | 90329509958 | 89953706054 | … |
| JavaEnable: | 1 | 0 | 1 | … |

34
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@ -210,7 +210,7 @@ Setting `format_template_resultset` specifies the path to file, which contains a
- `min` is the row with minimum values in `format_template_row` format (when extremes are set to 1)
- `max` is the row with maximum values in `format_template_row` format (when extremes are set to 1)
- `rows` is the total number of output rows
- `rows_before_limit` is the minimal number of rows there would have been without LIMIT. Output only if the query contains LIMIT. If the query contains GROUP BY, rows\_before\_limit\_at\_least is the exact number of rows there would have been without a LIMIT.
- `rows_before_limit` is the minimal number of rows there would have been without LIMIT. Output only if the query contains LIMIT. If the query contains GROUP BY, rows_before_limit_at_least is the exact number of rows there would have been without a LIMIT.
- `time` is the request execution time in seconds
- `rows_read` is the number of rows has been read
- `bytes_read` is the number of bytes (uncompressed) has been read
@ -361,21 +361,21 @@ Parsing allows the presence of the additional field `tskv` without the equal sig
Comma Separated Values format ([RFC](https://tools.ietf.org/html/rfc4180)).
When formatting, rows are enclosed in double-quotes. A double quote inside a string is output as two double quotes in a row. There are no other rules for escaping characters. Date and date-time are enclosed in double-quotes. Numbers are output without quotes. Values are separated by a delimiter character, which is `,` by default. The delimiter character is defined in the setting [format\_csv\_delimiter](../operations/settings/settings.md#settings-format_csv_delimiter). Rows are separated using the Unix line feed (LF). Arrays are serialized in CSV as follows: first, the array is serialized to a string as in TabSeparated format, and then the resulting string is output to CSV in double-quotes. Tuples in CSV format are serialized as separate columns (that is, their nesting in the tuple is lost).
When formatting, rows are enclosed in double-quotes. A double quote inside a string is output as two double quotes in a row. There are no other rules for escaping characters. Date and date-time are enclosed in double-quotes. Numbers are output without quotes. Values are separated by a delimiter character, which is `,` by default. The delimiter character is defined in the setting [format_csv_delimiter](../operations/settings/settings.md#settings-format_csv_delimiter). Rows are separated using the Unix line feed (LF). Arrays are serialized in CSV as follows: first, the array is serialized to a string as in TabSeparated format, and then the resulting string is output to CSV in double-quotes. Tuples in CSV format are serialized as separate columns (that is, their nesting in the tuple is lost).
``` bash
$ clickhouse-client --format_csv_delimiter="|" --query="INSERT INTO test.csv FORMAT CSV" < data.csv
```
\*By default, the delimiter is `,`. See the [format\_csv\_delimiter](../operations/settings/settings.md#settings-format_csv_delimiter) setting for more information.
\*By default, the delimiter is `,`. See the [format_csv_delimiter](../operations/settings/settings.md#settings-format_csv_delimiter) setting for more information.
When parsing, all values can be parsed either with or without quotes. Both double and single quotes are supported. Rows can also be arranged without quotes. In this case, they are parsed up to the delimiter character or line feed (CR or LF). In violation of the RFC, when parsing rows without quotes, the leading and trailing spaces and tabs are ignored. For the line feed, Unix (LF), Windows (CR LF) and Mac OS Classic (CR LF) types are all supported.
Empty unquoted input values are replaced with default values for the respective columns, if
[input\_format\_defaults\_for\_omitted\_fields](../operations/settings/settings.md#session_settings-input_format_defaults_for_omitted_fields)
[input_format_defaults_for_omitted_fields](../operations/settings/settings.md#session_settings-input_format_defaults_for_omitted_fields)
is enabled.
`NULL` is formatted as `\N` or `NULL` or an empty unquoted string (see settings [input\_format\_csv\_unquoted\_null\_literal\_as\_null](../operations/settings/settings.md#settings-input_format_csv_unquoted_null_literal_as_null) and [input\_format\_defaults\_for\_omitted\_fields](../operations/settings/settings.md#session_settings-input_format_defaults_for_omitted_fields)).
`NULL` is formatted as `\N` or `NULL` or an empty unquoted string (see settings [input_format_csv_unquoted_null_literal_as_null](../operations/settings/settings.md#settings-input_format_csv_unquoted_null_literal_as_null) and [input_format_defaults_for_omitted_fields](../operations/settings/settings.md#session_settings-input_format_defaults_for_omitted_fields)).
The CSV format supports the output of totals and extremes the same way as `TabSeparated`.
@ -439,12 +439,12 @@ SELECT SearchPhrase, count() AS c FROM test.hits GROUP BY SearchPhrase WITH TOTA
}
```
The JSON is compatible with JavaScript. To ensure this, some characters are additionally escaped: the slash `/` is escaped as `\/`; alternative line breaks `U+2028` and `U+2029`, which break some browsers, are escaped as `\uXXXX`. ASCII control characters are escaped: backspace, form feed, line feed, carriage return, and horizontal tab are replaced with `\b`, `\f`, `\n`, `\r`, `\t` , as well as the remaining bytes in the 00-1F range using `\uXXXX` sequences. Invalid UTF-8 sequences are changed to the replacement character <20> so the output text will consist of valid UTF-8 sequences. For compatibility with JavaScript, Int64 and UInt64 integers are enclosed in double-quotes by default. To remove the quotes, you can set the configuration parameter [output\_format\_json\_quote\_64bit\_integers](../operations/settings/settings.md#session_settings-output_format_json_quote_64bit_integers) to 0.
The JSON is compatible with JavaScript. To ensure this, some characters are additionally escaped: the slash `/` is escaped as `\/`; alternative line breaks `U+2028` and `U+2029`, which break some browsers, are escaped as `\uXXXX`. ASCII control characters are escaped: backspace, form feed, line feed, carriage return, and horizontal tab are replaced with `\b`, `\f`, `\n`, `\r`, `\t` , as well as the remaining bytes in the 00-1F range using `\uXXXX` sequences. Invalid UTF-8 sequences are changed to the replacement character <20> so the output text will consist of valid UTF-8 sequences. For compatibility with JavaScript, Int64 and UInt64 integers are enclosed in double-quotes by default. To remove the quotes, you can set the configuration parameter [output_format_json_quote_64bit_integers](../operations/settings/settings.md#session_settings-output_format_json_quote_64bit_integers) to 0.
`rows` – The total number of output rows.
`rows_before_limit_at_least` The minimal number of rows there would have been without LIMIT. Output only if the query contains LIMIT.
If the query contains GROUP BY, rows\_before\_limit\_at\_least is the exact number of rows there would have been without a LIMIT.
If the query contains GROUP BY, rows_before_limit_at_least is the exact number of rows there would have been without a LIMIT.
`totals` – Total values (when using WITH TOTALS).
@ -452,7 +452,7 @@ If the query contains GROUP BY, rows\_before\_limit\_at\_least is the exact numb
This format is only appropriate for outputting a query result, but not for parsing (retrieving data to insert in a table).
ClickHouse supports [NULL](../sql-reference/syntax.md), which is displayed as `null` in the JSON output. To enable `+nan`, `-nan`, `+inf`, `-inf` values in output, set the [output\_format\_json\_quote\_denormals](../operations/settings/settings.md#settings-output_format_json_quote_denormals) to 1.
ClickHouse supports [NULL](../sql-reference/syntax.md), which is displayed as `null` in the JSON output. To enable `+nan`, `-nan`, `+inf`, `-inf` values in output, set the [output_format_json_quote_denormals](../operations/settings/settings.md#settings-output_format_json_quote_denormals) to 1.
See also the [JSONEachRow](#jsoneachrow) format.
@ -633,7 +633,7 @@ ClickHouse ignores spaces between elements and commas after the objects. You can
ClickHouse substitutes omitted values with the default values for the corresponding [data types](../sql-reference/data-types/index.md).
If `DEFAULT expr` is specified, ClickHouse uses different substitution rules depending on the [input\_format\_defaults\_for\_omitted\_fields](../operations/settings/settings.md#session_settings-input_format_defaults_for_omitted_fields) setting.
If `DEFAULT expr` is specified, ClickHouse uses different substitution rules depending on the [input_format_defaults_for_omitted_fields](../operations/settings/settings.md#session_settings-input_format_defaults_for_omitted_fields) setting.
Consider the following table:
@ -676,7 +676,7 @@ Unlike the [JSON](#json) format, there is no substitution of invalid UTF-8 seque
### Usage of Nested Structures {#jsoneachrow-nested}
If you have a table with [Nested](../sql-reference/data-types/nested-data-structures/nested.md) data type columns, you can insert JSON data with the same structure. Enable this feature with the [input\_format\_import\_nested\_json](../operations/settings/settings.md#settings-input_format_import_nested_json) setting.
If you have a table with [Nested](../sql-reference/data-types/nested-data-structures/nested.md) data type columns, you can insert JSON data with the same structure. Enable this feature with the [input_format_import_nested_json](../operations/settings/settings.md#settings-input_format_import_nested_json) setting.
For example, consider the following table:
@ -690,7 +690,7 @@ As you can see in the `Nested` data type description, ClickHouse treats each com
INSERT INTO json_each_row_nested FORMAT JSONEachRow {"n.s": ["abc", "def"], "n.i": [1, 23]}
```
To insert data as a hierarchical JSON object, set [input\_format\_import\_nested\_json=1](../operations/settings/settings.md#settings-input_format_import_nested_json).
To insert data as a hierarchical JSON object, set [input_format_import_nested_json=1](../operations/settings/settings.md#settings-input_format_import_nested_json).
``` json
{
@ -872,7 +872,7 @@ The minimum set of characters that you need to escape when passing data in Value
This is the format that is used in `INSERT INTO t VALUES ...`, but you can also use it for formatting query results.
See also: [input\_format\_values\_interpret\_expressions](../operations/settings/settings.md#settings-input_format_values_interpret_expressions) and [input\_format\_values\_deduce\_templates\_of\_expressions](../operations/settings/settings.md#settings-input_format_values_deduce_templates_of_expressions) settings.
See also: [input_format_values_interpret_expressions](../operations/settings/settings.md#settings-input_format_values_interpret_expressions) and [input_format_values_deduce_templates_of_expressions](../operations/settings/settings.md#settings-input_format_values_deduce_templates_of_expressions) settings.
## Vertical {#vertical}
@ -1135,7 +1135,7 @@ Column names must:
- start with `[A-Za-z_]`
- subsequently contain only `[A-Za-z0-9_]`
Output Avro file compression and sync interval can be configured with [output\_format\_avro\_codec](../operations/settings/settings.md#settings-output_format_avro_codec) and [output\_format\_avro\_sync\_interval](../operations/settings/settings.md#settings-output_format_avro_sync_interval) respectively.
Output Avro file compression and sync interval can be configured with [output_format_avro_codec](../operations/settings/settings.md#settings-output_format_avro_codec) and [output_format_avro_sync_interval](../operations/settings/settings.md#settings-output_format_avro_sync_interval) respectively.
## AvroConfluent {#data-format-avro-confluent}
@ -1145,7 +1145,7 @@ Each Avro message embeds a schema id that can be resolved to the actual schema w
Schemas are cached once resolved.
Schema Registry URL is configured with [format\_avro\_schema\_registry\_url](../operations/settings/settings.md#format_avro_schema_registry_url).
Schema Registry URL is configured with [format_avro_schema_registry_url](../operations/settings/settings.md#format_avro_schema_registry_url).
### Data Types Matching {#data_types-matching-1}
@ -1298,13 +1298,13 @@ can contain an absolute path or a path relative to the current directory on the
If you use the client in the [batch mode](../interfaces/cli.md#cli_usage), the path to the schema must be relative due to security reasons.
If you input or output data via the [HTTP interface](../interfaces/http.md) the file name specified in the format schema
should be located in the directory specified in [format\_schema\_path](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-format_schema_path)
should be located in the directory specified in [format_schema_path](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-format_schema_path)
in the server configuration.
## Skipping Errors {#skippingerrors}
Some formats such as `CSV`, `TabSeparated`, `TSKV`, `JSONEachRow`, `Template`, `CustomSeparated` and `Protobuf` can skip broken row if parsing error occurred and continue parsing from the beginning of next row. See [input\_format\_allow\_errors\_num](../operations/settings/settings.md#settings-input_format_allow_errors_num) and
[input\_format\_allow\_errors\_ratio](../operations/settings/settings.md#settings-input_format_allow_errors_ratio) settings.
Some formats such as `CSV`, `TabSeparated`, `TSKV`, `JSONEachRow`, `Template`, `CustomSeparated` and `Protobuf` can skip broken row if parsing error occurred and continue parsing from the beginning of next row. See [input_format_allow_errors_num](../operations/settings/settings.md#settings-input_format_allow_errors_num) and
[input_format_allow_errors_ratio](../operations/settings/settings.md#settings-input_format_allow_errors_ratio) settings.
Limitations:
- In case of parsing error `JSONEachRow` skips all data until the new line (or EOF), so rows must be delimited by `\n` to count errors correctly.
- `Template` and `CustomSeparated` use delimiter after the last column and delimiter between rows to find the beginning of next row, so skipping errors works only if at least one of them is not empty.

26
docs/en/interfaces/http.md
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@ -9,7 +9,7 @@ The HTTP interface lets you use ClickHouse on any platform from any programming
By default, clickhouse-server listens for HTTP on port 8123 (this can be changed in the config).
If you make a GET / request without parameters, it returns 200 response code and the string which defined in [http\_server\_default\_response](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-http_server_default_response) default value “Ok.” (with a line feed at the end)
If you make a GET / request without parameters, it returns 200 response code and the string which defined in [http_server_default_response](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-http_server_default_response) default value “Ok.” (with a line feed at the end)
``` bash
$ curl 'http://localhost:8123/'
@ -148,12 +148,12 @@ $ echo 'DROP TABLE t' | curl 'http://localhost:8123/' --data-binary @-
For successful requests that don’t return a data table, an empty response body is returned.
You can use the internal ClickHouse compression format when transmitting data. The compressed data has a non-standard format, and you will need to use the special `clickhouse-compressor` program to work with it (it is installed with the `clickhouse-client` package). To increase the efficiency of data insertion, you can disable server-side checksum verification by using the [http\_native\_compression\_disable\_checksumming\_on\_decompress](../operations/settings/settings.md#settings-http_native_compression_disable_checksumming_on_decompress) setting.
You can use the internal ClickHouse compression format when transmitting data. The compressed data has a non-standard format, and you will need to use the special `clickhouse-compressor` program to work with it (it is installed with the `clickhouse-client` package). To increase the efficiency of data insertion, you can disable server-side checksum verification by using the [http_native_compression_disable_checksumming_on_decompress](../operations/settings/settings.md#settings-http_native_compression_disable_checksumming_on_decompress) setting.
If you specified `compress=1` in the URL, the server compresses the data it sends you.
If you specified `decompress=1` in the URL, the server decompresses the same data that you pass in the `POST` method.
You can also choose to use [HTTP compression](https://en.wikipedia.org/wiki/HTTP_compression). To send a compressed `POST` request, append the request header `Content-Encoding: compression_method`. In order for ClickHouse to compress the response, you must append `Accept-Encoding: compression_method`. ClickHouse supports `gzip`, `br`, and `deflate` [compression methods](https://en.wikipedia.org/wiki/HTTP_compression#Content-Encoding_tokens). To enable HTTP compression, you must use the ClickHouse [enable\_http\_compression](../operations/settings/settings.md#settings-enable_http_compression) setting. You can configure the data compression level in the [http\_zlib\_compression\_level](#settings-http_zlib_compression_level) setting for all the compression methods.
You can also choose to use [HTTP compression](https://en.wikipedia.org/wiki/HTTP_compression). To send a compressed `POST` request, append the request header `Content-Encoding: compression_method`. In order for ClickHouse to compress the response, you must append `Accept-Encoding: compression_method`. ClickHouse supports `gzip`, `br`, and `deflate` [compression methods](https://en.wikipedia.org/wiki/HTTP_compression#Content-Encoding_tokens). To enable HTTP compression, you must use the ClickHouse [enable_http_compression](../operations/settings/settings.md#settings-enable_http_compression) setting. You can configure the data compression level in the [http_zlib_compression_level](#settings-http_zlib_compression_level) setting for all the compression methods.
You can use this to reduce network traffic when transmitting a large amount of data, or for creating dumps that are immediately compressed.
@ -215,7 +215,7 @@ $ echo 'SELECT 1' | curl -H 'X-ClickHouse-User: user' -H 'X-ClickHouse-Key: pass
```
If the user name is not specified, the `default` name is used. If the password is not specified, the empty password is used.
You can also use the URL parameters to specify any settings for processing a single query or entire profiles of settings. Example:http://localhost:8123/?profile=web&max\_rows\_to\_read=1000000000&query=SELECT+1
You can also use the URL parameters to specify any settings for processing a single query or entire profiles of settings. Example:http://localhost:8123/?profile=web&max_rows_to_read=1000000000&query=SELECT+1
For more information, see the [Settings](../operations/settings/index.md) section.
@ -237,7 +237,7 @@ For information about other parameters, see the section “SET”.
Similarly, you can use ClickHouse sessions in the HTTP protocol. To do this, you need to add the `session_id` GET parameter to the request. You can use any string as the session ID. By default, the session is terminated after 60 seconds of inactivity. To change this timeout, modify the `default_session_timeout` setting in the server configuration, or add the `session_timeout` GET parameter to the request. To check the session status, use the `session_check=1` parameter. Only one query at a time can be executed within a single session.
You can receive information about the progress of a query in `X-ClickHouse-Progress` response headers. To do this, enable [send\_progress\_in\_http\_headers](../operations/settings/settings.md#settings-send_progress_in_http_headers). Example of the header sequence:
You can receive information about the progress of a query in `X-ClickHouse-Progress` response headers. To do this, enable [send_progress_in_http_headers](../operations/settings/settings.md#settings-send_progress_in_http_headers). Example of the header sequence:
``` text
X-ClickHouse-Progress: {"read_rows":"2752512","read_bytes":"240570816","total_rows_to_read":"8880128"}
@ -254,9 +254,9 @@ Possible header fields:
- `written_bytes` — Volume of data written in bytes.
Running requests don’t stop automatically if the HTTP connection is lost. Parsing and data formatting are performed on the server-side, and using the network might be ineffective.
The optional ‘query\_id’ parameter can be passed as the query ID (any string). For more information, see the section “Settings, replace\_running\_query”.
The optional ‘query_id’ parameter can be passed as the query ID (any string). For more information, see the section “Settings, replace_running_query”.
The optional ‘quota\_key’ parameter can be passed as the quota key (any string). For more information, see the section “Quotas”.
The optional ‘quota_key’ parameter can be passed as the quota key (any string). For more information, see the section “Quotas”.
The HTTP interface allows passing external data (external temporary tables) for querying. For more information, see the section “External data for query processing”.
@ -377,7 +377,7 @@ Now `rule` can configure `method`, `headers`, `url`, `handler`:
- `headers` are responsible for matching the header part of the HTTP request. It is compatible with RE2’s regular expressions. It is an optional configuration. If it is not defined in the configuration file, it does not match the header portion of the HTTP request.
- `handler` contains the main processing part. Now `handler` can configure `type`, `status`, `content_type`, `response_content`, `query`, `query_param_name`.
`type` currently supports three types: [predefined\_query\_handler](#predefined_query_handler), [dynamic\_query\_handler](#dynamic_query_handler), [static](#static).
`type` currently supports three types: [predefined_query_handler](#predefined_query_handler), [dynamic_query_handler](#dynamic_query_handler), [static](#static).
- `query` — use with `predefined_query_handler` type, executes query when the handler is called.
@ -391,13 +391,13 @@ Now `rule` can configure `method`, `headers`, `url`, `handler`:
Next are the configuration methods for different `type`.
### predefined\_query\_handler {#predefined_query_handler}
### predefined_query_handler {#predefined_query_handler}
`predefined_query_handler` supports setting `Settings` and `query_params` values. You can configure `query` in the type of `predefined_query_handler`.
`query` value is a predefined query of `predefined_query_handler`, which is executed by ClickHouse when an HTTP request is matched and the result of the query is returned. It is a must configuration.
The following example defines the values of [max\_threads](../operations/settings/settings.md#settings-max_threads) and `max_alter_threads` settings, then queries the system table to check whether these settings were set successfully.
The following example defines the values of [max_threads](../operations/settings/settings.md#settings-max_threads) and `max_alter_threads` settings, then queries the system table to check whether these settings were set successfully.
Example:
@ -428,13 +428,13 @@ max_alter_threads 2
!!! note "caution"
In one `predefined_query_handler` only supports one `query` of an insert type.
### dynamic\_query\_handler {#dynamic_query_handler}
### dynamic_query_handler {#dynamic_query_handler}
In `dynamic_query_handler`, the query is written in the form of param of the HTTP request. The difference is that in `predefined_query_handler`, the query is written in the configuration file. You can configure `query_param_name` in `dynamic_query_handler`.
ClickHouse extracts and executes the value corresponding to the `query_param_name` value in the URL of the HTTP request. The default value of `query_param_name` is `/query` . It is an optional configuration. If there is no definition in the configuration file, the param is not passed in.
To experiment with this functionality, the example defines the values of [max\_threads](../operations/settings/settings.md#settings-max_threads) and `max_alter_threads` and `queries` whether the settings were set successfully.
To experiment with this functionality, the example defines the values of [max_threads](../operations/settings/settings.md#settings-max_threads) and `max_alter_threads` and `queries` whether the settings were set successfully.
Example:
@ -459,7 +459,7 @@ max_alter_threads 2
### static {#static}
`static` can return [content\_type](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Type), [status](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status) and `response_content`. `response_content` can return the specified content.
`static` can return [content_type](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Type), [status](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status) and `response_content`. `response_content` can return the specified content.
Example:

2
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@ -5,7 +5,7 @@ toc_title: MySQL Interface
# MySQL Interface {#mysql-interface}
ClickHouse supports MySQL wire protocol. It can be enabled by [mysql\_port](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-mysql_port) setting in configuration file:
ClickHouse supports MySQL wire protocol. It can be enabled by [mysql_port](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-mysql_port) setting in configuration file:
``` xml
<mysql_port>9004</mysql_port>

4
docs/en/interfaces/third-party/client-libraries.md vendored
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@ -9,7 +9,7 @@ toc_title: Client Libraries
Yandex does **not** maintain the libraries listed below and haven’t done any extensive testing to ensure their quality.
- Python
- [infi.clickhouse\_orm](https://github.com/Infinidat/infi.clickhouse_orm)
- [infi.clickhouse_orm](https://github.com/Infinidat/infi.clickhouse_orm)
- [clickhouse-driver](https://github.com/mymarilyn/clickhouse-driver)
- [clickhouse-client](https://github.com/yurial/clickhouse-client)
- [aiochclient](https://github.com/maximdanilchenko/aiochclient)
@ -46,7 +46,7 @@ toc_title: Client Libraries
- [clickhouse-scala-client](https://github.com/crobox/clickhouse-scala-client)
- Kotlin
- [AORM](https://github.com/TanVD/AORM)
- C\#
- C#
- [Octonica.ClickHouseClient](https://github.com/Octonica/ClickHouseClient)
- [ClickHouse.Ado](https://github.com/killwort/ClickHouse-Net)
- [ClickHouse.Client](https://github.com/DarkWanderer/ClickHouse.Client)

22
docs/en/interfaces/third-party/integrations.md vendored
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@ -17,15 +17,15 @@ toc_title: Integrations
- [clickhouse-mysql-data-reader](https://github.com/Altinity/clickhouse-mysql-data-reader)
- [horgh-replicator](https://github.com/larsnovikov/horgh-replicator)
- [PostgreSQL](https://www.postgresql.org)
- [clickhousedb\_fdw](https://github.com/Percona-Lab/clickhousedb_fdw)
- [infi.clickhouse\_fdw](https://github.com/Infinidat/infi.clickhouse_fdw) (uses [infi.clickhouse\_orm](https://github.com/Infinidat/infi.clickhouse_orm))
- [clickhousedb_fdw](https://github.com/Percona-Lab/clickhousedb_fdw)
- [infi.clickhouse_fdw](https://github.com/Infinidat/infi.clickhouse_fdw) (uses [infi.clickhouse_orm](https://github.com/Infinidat/infi.clickhouse_orm))
- [pg2ch](https://github.com/mkabilov/pg2ch)
- [clickhouse\_fdw](https://github.com/adjust/clickhouse_fdw)
- [clickhouse_fdw](https://github.com/adjust/clickhouse_fdw)
- [MSSQL](https://en.wikipedia.org/wiki/Microsoft_SQL_Server)
- [ClickHouseMigrator](https://github.com/zlzforever/ClickHouseMigrator)
- Message queues
- [Kafka](https://kafka.apache.org)
- [clickhouse\_sinker](https://github.com/housepower/clickhouse_sinker) (uses [Go client](https://github.com/ClickHouse/clickhouse-go/))
- [clickhouse_sinker](https://github.com/housepower/clickhouse_sinker) (uses [Go client](https://github.com/ClickHouse/clickhouse-go/))
- [stream-loader-clickhouse](https://github.com/adform/stream-loader)
- Stream processing
- [Flink](https://flink.apache.org)
@ -49,12 +49,12 @@ toc_title: Integrations
- [Grafana](https://grafana.com/)
- [clickhouse-grafana](https://github.com/Vertamedia/clickhouse-grafana)
- [Prometheus](https://prometheus.io/)
- [clickhouse\_exporter](https://github.com/f1yegor/clickhouse_exporter)
- [clickhouse_exporter](https://github.com/f1yegor/clickhouse_exporter)
- [PromHouse](https://github.com/Percona-Lab/PromHouse)
- [clickhouse\_exporter](https://github.com/hot-wifi/clickhouse_exporter) (uses [Go client](https://github.com/kshvakov/clickhouse/))
- [clickhouse_exporter](https://github.com/hot-wifi/clickhouse_exporter) (uses [Go client](https://github.com/kshvakov/clickhouse/))
- [Nagios](https://www.nagios.org/)
- [check\_clickhouse](https://github.com/exogroup/check_clickhouse/)
- [check\_clickhouse.py](https://github.com/innogames/igmonplugins/blob/master/src/check_clickhouse.py)
- [check_clickhouse](https://github.com/exogroup/check_clickhouse/)
- [check_clickhouse.py](https://github.com/innogames/igmonplugins/blob/master/src/check_clickhouse.py)
- [Zabbix](https://www.zabbix.com)
- [clickhouse-zabbix-template](https://github.com/Altinity/clickhouse-zabbix-template)
- [Sematext](https://sematext.com/)
@ -74,7 +74,7 @@ toc_title: Integrations
- Python
- [SQLAlchemy](https://www.sqlalchemy.org)
- [sqlalchemy-clickhouse](https://github.com/cloudflare/sqlalchemy-clickhouse) (uses [infi.clickhouse\_orm](https://github.com/Infinidat/infi.clickhouse_orm))
- [sqlalchemy-clickhouse](https://github.com/cloudflare/sqlalchemy-clickhouse) (uses [infi.clickhouse_orm](https://github.com/Infinidat/infi.clickhouse_orm))
- [pandas](https://pandas.pydata.org)
- [pandahouse](https://github.com/kszucs/pandahouse)
- PHP
@ -89,7 +89,7 @@ toc_title: Integrations
- Scala
- [Akka](https://akka.io)
- [clickhouse-scala-client](https://github.com/crobox/clickhouse-scala-client)
- C\#
- C#
- [ADO.NET](https://docs.microsoft.com/en-us/dotnet/framework/data/adonet/ado-net-overview)
- [ClickHouse.Ado](https://github.com/killwort/ClickHouse-Net)
- [ClickHouse.Client](https://github.com/DarkWanderer/ClickHouse.Client)
@ -97,7 +97,7 @@ toc_title: Integrations
- [ClickHouse.Net.Migrations](https://github.com/ilyabreev/ClickHouse.Net.Migrations)
- Elixir
- [Ecto](https://github.com/elixir-ecto/ecto)
- [clickhouse\_ecto](https://github.com/appodeal/clickhouse_ecto)
- [clickhouse_ecto](https://github.com/appodeal/clickhouse_ecto)
- Ruby
- [Ruby on Rails](https://rubyonrails.org/)
- [activecube](https://github.com/bitquery/activecube)

1
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@ -60,6 +60,7 @@ toc_title: Adopters
| <a href="https://lifestreet.com/" class="favicon">LifeStreet</a> | Ad network | Main product | 75 servers (3 replicas) | 5.27 PiB | [Blog post in Russian, February 2017](https://habr.com/en/post/322620/) |
| <a href="https://mcs.mail.ru/" class="favicon">Mail.ru Cloud Solutions</a> | Cloud services | Main product | — | — | [Article in Russian](https://mcs.mail.ru/help/db-create/clickhouse#) |
| <a href="https://tech.mymarilyn.ru" class="favicon">Marilyn</a> | Advertising | Statistics | — | — | [Talk in Russian, June 2017](https://www.youtube.com/watch?v=iXlIgx2khwc) |
| <a href="https://mellodesign.ru/" class="favicon">Mello</a> | Marketing | Analytics | 1 server | — | [Article, Oct 2020](https://vc.ru/marketing/166180-razrabotka-tipovogo-otcheta-skvoznoy-analitiki) |
| <a href="https://www.messagebird.com" class="favicon">MessageBird</a> | Telecommunications | Statistics | — | — | [Slides in English, November 2018](https://github.com/ClickHouse/clickhouse-presentations/blob/master/meetup20/messagebird.pdf) |
| <a href="https://www.mindsdb.com/" class="favicon">MindsDB</a> | Machine Learning | Main Product | — | — | [Official Website](https://www.mindsdb.com/blog/machine-learning-models-as-tables-in-ch) |
| <a href="https://www.mgid.com/" class="favicon">MGID</a> | Ad network | Web-analytics | — | — | [Blog post in Russian, April 2020](http://gs-studio.com/news-about-it/32777----clickhouse---c) |

4
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@ -138,10 +138,10 @@ Management queries:
- Setup a directory for configurations storage.
ClickHouse stores access entity configurations in the folder set in the [access\_control\_path](../operations/server-configuration-parameters/settings.md#access_control_path) server configuration parameter.
ClickHouse stores access entity configurations in the folder set in the [access_control_path](../operations/server-configuration-parameters/settings.md#access_control_path) server configuration parameter.
- Enable SQL-driven access control and account management for at least one user account.
By default, SQL-driven access control and account management is disabled for all users. You need to configure at least one user in the `users.xml` configuration file and set the value of the [access\_management](../operations/settings/settings-users.md#access_management-user-setting) setting to 1.
By default, SQL-driven access control and account management is disabled for all users. You need to configure at least one user in the `users.xml` configuration file and set the value of the [access_management](../operations/settings/settings-users.md#access_management-user-setting) setting to 1.
[Original article](https://clickhouse.tech/docs/en/operations/access_rights/) <!--hide-->

2
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@ -20,7 +20,7 @@ Some settings specified in the main configuration file can be overridden in othe
## Substitution {#substitution}
The config can also define “substitutions”. If an element has the `incl` attribute, the corresponding substitution from the file will be used as the value. By default, the path to the file with substitutions is `/etc/metrika.xml`. This can be changed in the [include\_from](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-include_from) element in the server config. The substitution values are specified in `/yandex/substitution_name` elements in this file. If a substitution specified in `incl` does not exist, it is recorded in the log. To prevent ClickHouse from logging missing substitutions, specify the `optional="true"` attribute (for example, settings for [macros](../operations/server-configuration-parameters/settings.md)).
The config can also define “substitutions”. If an element has the `incl` attribute, the corresponding substitution from the file will be used as the value. By default, the path to the file with substitutions is `/etc/metrika.xml`. This can be changed in the [include_from](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-include_from) element in the server config. The substitution values are specified in `/yandex/substitution_name` elements in this file. If a substitution specified in `incl` does not exist, it is recorded in the log. To prevent ClickHouse from logging missing substitutions, specify the `optional="true"` attribute (for example, settings for [macros](../operations/server-configuration-parameters/settings.md)).
Substitutions can also be performed from ZooKeeper. To do this, specify the attribute `from_zk = "/path/to/node"`. The element value is replaced with the contents of the node at `/path/to/node` in ZooKeeper. You can also put an entire XML subtree on the ZooKeeper node and it will be fully inserted into the source element.

4
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@ -33,7 +33,7 @@ ClickHouse collects:
- Different metrics of how the server uses computational resources.
- Common statistics on query processing.
You can find metrics in the [system.metrics](../operations/system-tables/metrics.md#system_tables-metrics), [system.events](../operations/system-tables/events.md#system_tables-events), and [system.asynchronous\_metrics](../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) tables.
You can find metrics in the [system.metrics](../operations/system-tables/metrics.md#system_tables-metrics), [system.events](../operations/system-tables/events.md#system_tables-events), and [system.asynchronous_metrics](../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) tables.
You can configure ClickHouse to export metrics to [Graphite](https://github.com/graphite-project). See the [Graphite section](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-graphite) in the ClickHouse server configuration file. Before configuring export of metrics, you should set up Graphite by following their official [guide](https://graphite.readthedocs.io/en/latest/install.html).
@ -41,4 +41,4 @@ You can configure ClickHouse to export metrics to [Prometheus](https://prometheu
Additionally, you can monitor server availability through the HTTP API. Send the `HTTP GET` request to `/ping`. If the server is available, it responds with `200 OK`.
To monitor servers in a cluster configuration, you should set the [max\_replica\_delay\_for\_distributed\_queries](../operations/settings/settings.md#settings-max_replica_delay_for_distributed_queries) parameter and use the HTTP resource `/replicas_status`. A request to `/replicas_status` returns `200 OK` if the replica is available and is not delayed behind the other replicas. If a replica is delayed, it returns `503 HTTP_SERVICE_UNAVAILABLE` with information about the gap.
To monitor servers in a cluster configuration, you should set the [max_replica_delay_for_distributed_queries](../operations/settings/settings.md#settings-max_replica_delay_for_distributed_queries) parameter and use the HTTP resource `/replicas_status`. A request to `/replicas_status` returns `200 OK` if the replica is available and is not delayed behind the other replicas. If a replica is delayed, it returns `503 HTTP_SERVICE_UNAVAILABLE` with information about the gap.

8
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@ -9,11 +9,11 @@ ClickHouse runs sampling profiler that allows analyzing query execution. Using p
To use profiler:
- Setup the [trace\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-trace_log) section of the server configuration.
- Setup the [trace_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-trace_log) section of the server configuration.
This section configures the [trace\_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) system table containing the results of the profiler functioning. It is configured by default. Remember that data in this table is valid only for a running server. After the server restart, ClickHouse doesn’t clean up the table and all the stored virtual memory address may become invalid.
This section configures the [trace_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) system table containing the results of the profiler functioning. It is configured by default. Remember that data in this table is valid only for a running server. After the server restart, ClickHouse doesn’t clean up the table and all the stored virtual memory address may become invalid.
- Setup the [query\_profiler\_cpu\_time\_period\_ns](../../operations/settings/settings.md#query_profiler_cpu_time_period_ns) or [query\_profiler\_real\_time\_period\_ns](../../operations/settings/settings.md#query_profiler_real_time_period_ns) settings. Both settings can be used simultaneously.
- Setup the [query_profiler_cpu_time_period_ns](../../operations/settings/settings.md#query_profiler_cpu_time_period_ns) or [query_profiler_real_time_period_ns](../../operations/settings/settings.md#query_profiler_real_time_period_ns) settings. Both settings can be used simultaneously.
These settings allow you to configure profiler timers. As these are the session settings, you can get different sampling frequency for the whole server, individual users or user profiles, for your interactive session, and for each individual query.
@ -23,7 +23,7 @@ To analyze the `trace_log` system table:
- Install the `clickhouse-common-static-dbg` package. See [Install from DEB Packages](../../getting-started/install.md#install-from-deb-packages).
- Allow introspection functions by the [allow\_introspection\_functions](../../operations/settings/settings.md#settings-allow_introspection_functions) setting.
- Allow introspection functions by the [allow_introspection_functions](../../operations/settings/settings.md#settings-allow_introspection_functions) setting.
For security reasons, introspection functions are disabled by default.

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@ -7,7 +7,7 @@ toc_title: Requirements
## CPU {#cpu}
For installation from prebuilt deb packages, use a CPU with x86\_64 architecture and support for SSE 4.2 instructions. To run ClickHouse with processors that do not support SSE 4.2 or have AArch64 or PowerPC64LE architecture, you should build ClickHouse from sources.
For installation from prebuilt deb packages, use a CPU with x86_64 architecture and support for SSE 4.2 instructions. To run ClickHouse with processors that do not support SSE 4.2 or have AArch64 or PowerPC64LE architecture, you should build ClickHouse from sources.
ClickHouse implements parallel data processing and uses all the hardware resources available. When choosing a processor, take into account that ClickHouse works more efficiently at configurations with a large number of cores but a lower clock rate than at configurations with fewer cores and a higher clock rate. For example, 16 cores with 2600 MHz is preferable to 8 cores with 3600 MHz.

130
docs/en/operations/server-configuration-parameters/settings.md
View File

@ -5,7 +5,7 @@ toc_title: Server Settings
# Server Settings {#server-settings}
## builtin\_dictionaries\_reload\_interval {#builtin-dictionaries-reload-interval}
## builtin_dictionaries_reload_interval {#builtin-dictionaries-reload-interval}
The interval in seconds before reloading built-in dictionaries.
@ -92,7 +92,7 @@ Configures soft limit for core dump file size, one gigabyte by default.
(Hard limit is configured via system tools)
## default\_database {#default-database}
## default_database {#default-database}
The default database.
@ -104,7 +104,7 @@ To get a list of databases, use the [SHOW DATABASES](../../sql-reference/stateme
<default_database>default</default_database>
```
## default\_profile {#default-profile}
## default_profile {#default-profile}
Default settings profile.
@ -116,7 +116,7 @@ Settings profiles are located in the file specified in the parameter `user_confi
<default_profile>default</default_profile>
```
## dictionaries\_config {#server_configuration_parameters-dictionaries_config}
## dictionaries_config {#server_configuration_parameters-dictionaries_config}
The path to the config file for external dictionaries.
@ -133,7 +133,7 @@ See also “[External dictionaries](../../sql-reference/dictionaries/external-di
<dictionaries_config>*_dictionary.xml</dictionaries_config>
```
## dictionaries\_lazy\_load {#server_configuration_parameters-dictionaries_lazy_load}
## dictionaries_lazy_load {#server_configuration_parameters-dictionaries_lazy_load}
Lazy loading of dictionaries.
@ -149,7 +149,7 @@ The default is `true`.
<dictionaries_lazy_load>true</dictionaries_lazy_load>
```
## format\_schema\_path {#server_configuration_parameters-format_schema_path}
## format_schema_path {#server_configuration_parameters-format_schema_path}
The path to the directory with the schemes for the input data, such as schemas for the [CapnProto](../../interfaces/formats.md#capnproto) format.
@ -170,11 +170,11 @@ Settings:
- port – The port on the Graphite server.
- interval – The interval for sending, in seconds.
- timeout – The timeout for sending data, in seconds.
- root\_path – Prefix for keys.
- root_path – Prefix for keys.
- metrics – Sending data from the [system.metrics](../../operations/system-tables/metrics.md#system_tables-metrics) table.
- events – Sending deltas data accumulated for the time period from the [system.events](../../operations/system-tables/events.md#system_tables-events) table.
- events\_cumulative – Sending cumulative data from the [system.events](../../operations/system-tables/events.md#system_tables-events) table.
- asynchronous\_metrics – Sending data from the [system.asynchronous\_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) table.
- events_cumulative – Sending cumulative data from the [system.events](../../operations/system-tables/events.md#system_tables-events) table.
- asynchronous_metrics – Sending data from the [system.asynchronous_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) table.
You can configure multiple `<graphite>` clauses. For instance, you can use this for sending different data at different intervals.
@ -194,7 +194,7 @@ You can configure multiple `<graphite>` clauses. For instance, you can use this
</graphite>
```
## graphite\_rollup {#server_configuration_parameters-graphite-rollup}
## graphite_rollup {#server_configuration_parameters-graphite-rollup}
Settings for thinning data for Graphite.
@ -222,7 +222,7 @@ For more details, see [GraphiteMergeTree](../../engines/table-engines/mergetree-
</graphite_rollup_example>
```
## http\_port/https\_port {#http-porthttps-port}
## http_port/https_port {#http-porthttps-port}
The port for connecting to the server over HTTP(s).
@ -236,7 +236,7 @@ If `http_port` is specified, the OpenSSL configuration is ignored even if it is
<https_port>9999</https_port>
```
## http\_server\_default\_response {#server_configuration_parameters-http_server_default_response}
## http_server_default_response {#server_configuration_parameters-http_server_default_response}
The page that is shown by default when you access the ClickHouse HTTP(s) server.
The default value is “Ok.” (with a line feed at the end)
@ -251,7 +251,7 @@ Opens `https://tabix.io/` when accessing `http://localhost: http_port`.
</http_server_default_response>
```
## include\_from {#server_configuration_parameters-include_from}
## include_from {#server_configuration_parameters-include_from}
The path to the file with substitutions.
@ -263,7 +263,7 @@ For more information, see the section “[Configuration files](../../operations/
<include_from>/etc/metrica.xml</include_from>
```
## interserver\_http\_port {#interserver-http-port}
## interserver_http_port {#interserver-http-port}
Port for exchanging data between ClickHouse servers.
@ -273,7 +273,7 @@ Port for exchanging data between ClickHouse servers.
<interserver_http_port>9009</interserver_http_port>
```
## interserver\_http\_host {#interserver-http-host}
## interserver_http_host {#interserver-http-host}
The hostname that can be used by other servers to access this server.
@ -287,7 +287,7 @@ Useful for breaking away from a specific network interface.
<interserver_http_host>example.yandex.ru</interserver_http_host>
```
## interserver\_http\_credentials {#server-settings-interserver-http-credentials}
## interserver_http_credentials {#server-settings-interserver-http-credentials}
The username and password used to authenticate during [replication](../../engines/table-engines/mergetree-family/replication.md) with the Replicated\* engines. These credentials are used only for communication between replicas and are unrelated to credentials for ClickHouse clients. The server is checking these credentials for connecting replicas and use the same credentials when connecting to other replicas. So, these credentials should be set the same for all replicas in a cluster.
By default, the authentication is not used.
@ -306,7 +306,7 @@ This section contains the following parameters:
</interserver_http_credentials>
```
## keep\_alive\_timeout {#keep-alive-timeout}
## keep_alive_timeout {#keep-alive-timeout}
The number of seconds that ClickHouse waits for incoming requests before closing the connection. Defaults to 3 seconds.
@ -316,7 +316,7 @@ The number of seconds that ClickHouse waits for incoming requests before closing
<keep_alive_timeout>3</keep_alive_timeout>
```
## listen\_host {#server_configuration_parameters-listen_host}
## listen_host {#server_configuration_parameters-listen_host}
Restriction on hosts that requests can come from. If you want the server to answer all of them, specify `::`.
@ -367,14 +367,14 @@ Writing to the syslog is also supported. Config example:
Keys for syslog:
- use\_syslog — Required setting if you want to write to the syslog.
- use_syslog — Required setting if you want to write to the syslog.
- address — The host\[:port\] of syslogd. If omitted, the local daemon is used.
- hostname — Optional. The name of the host that logs are sent from.
- facility — [The syslog facility keyword](https://en.wikipedia.org/wiki/Syslog#Facility) in uppercase letters with the “LOG\_” prefix: (`LOG_USER`, `LOG_DAEMON`, `LOG_LOCAL3`, and so on).
- facility — [The syslog facility keyword](https://en.wikipedia.org/wiki/Syslog#Facility) in uppercase letters with the “LOG_” prefix: (`LOG_USER`, `LOG_DAEMON`, `LOG_LOCAL3`, and so on).
Default value: `LOG_USER` if `address` is specified, `LOG_DAEMON` otherwise.
- format – Message format. Possible values: `bsd` and `syslog.`
## send\_crash\_reports {#server_configuration_parameters-logger}
## send_crash_reports {#server_configuration_parameters-logger}
Settings for opt-in sending crash reports to the ClickHouse core developers team via [Sentry](https://sentry.io).
Enabling it, especially in pre-production environments, is highly appreciated.
@ -412,7 +412,7 @@ For more information, see the section “[Creating replicated tables](../../engi
<macros incl="macros" optional="true" />
```
## mark\_cache\_size {#server-mark-cache-size}
## mark_cache_size {#server-mark-cache-size}
Approximate size (in bytes) of the cache of marks used by table engines of the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) family.
@ -424,7 +424,7 @@ The cache is shared for the server and memory is allocated as needed. The cache
<mark_cache_size>5368709120</mark_cache_size>
```
## max\_server\_memory\_usage {#max_server_memory_usage}
## max_server_memory_usage {#max_server_memory_usage}
Limits total RAM usage by the ClickHouse server.
@ -441,7 +441,7 @@ The default `max_server_memory_usage` value is calculated as `memory_amount * ma
**See also**
- [max\_memory\_usage](../../operations/settings/query-complexity.md#settings_max_memory_usage)
- [max_memory_usage](../../operations/settings/query-complexity.md#settings_max_memory_usage)
- [max_server_memory_usage_to_ram_ratio](#max_server_memory_usage_to_ram_ratio)
## max_server_memory_usage_to_ram_ratio {#max_server_memory_usage_to_ram_ratio}
@ -469,7 +469,7 @@ On hosts with low RAM and swap, you possibly need setting `max_server_memory_usa
- [max_server_memory_usage](#max_server_memory_usage)
## max\_concurrent\_queries {#max-concurrent-queries}
## max_concurrent_queries {#max-concurrent-queries}
The maximum number of simultaneously processed requests.
@ -479,7 +479,7 @@ The maximum number of simultaneously processed requests.
<max_concurrent_queries>100</max_concurrent_queries>
```
## max\_connections {#max-connections}
## max_connections {#max-connections}
The maximum number of inbound connections.
@ -489,7 +489,7 @@ The maximum number of inbound connections.
<max_connections>4096</max_connections>
```
## max\_open\_files {#max-open-files}
## max_open_files {#max-open-files}
The maximum number of open files.
@ -503,7 +503,7 @@ We recommend using this option in Mac OS X since the `getrlimit()` function retu
<max_open_files>262144</max_open_files>
```
## max\_table\_size\_to\_drop {#max-table-size-to-drop}
## max_table_size_to_drop {#max-table-size-to-drop}
Restriction on deleting tables.
@ -521,7 +521,7 @@ The value 0 means that you can delete all tables without any restrictions.
<max_table_size_to_drop>0</max_table_size_to_drop>
```
## max\_thread\_pool\_size {#max-thread-pool-size}
## max_thread_pool_size {#max-thread-pool-size}
The maximum number of threads in the Global Thread pool.
@ -533,7 +533,7 @@ Default value: 10000.
<max_thread_pool_size>12000</max_thread_pool_size>
```
## merge\_tree {#server_configuration_parameters-merge_tree}
## merge_tree {#server_configuration_parameters-merge_tree}
Fine tuning for tables in the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md).
@ -547,7 +547,7 @@ For more information, see the MergeTreeSettings.h header file.
</merge_tree>
```
## replicated\_merge\_tree {#server_configuration_parameters-replicated_merge_tree}
## replicated_merge_tree {#server_configuration_parameters-replicated_merge_tree}
Fine tuning for tables in the [ReplicatedMergeTree](../../engines/table-engines/mergetree-family/mergetree.md).
@ -584,7 +584,7 @@ Keys for server/client settings:
- sessionTimeout – Time for caching the session on the server.
- extendedVerification – Automatically extended verification of certificates after the session ends. Acceptable values: `true`, `false`.
- requireTLSv1 – Require a TLSv1 connection. Acceptable values: `true`, `false`.
- requireTLSv1\_1 – Require a TLSv1.1 connection. Acceptable values: `true`, `false`.
- requireTLSv1_1 – Require a TLSv1.1 connection. Acceptable values: `true`, `false`.
- requireTLSv1 – Require a TLSv1.2 connection. Acceptable values: `true`, `false`.
- fips – Activates OpenSSL FIPS mode. Supported if the library’s OpenSSL version supports FIPS.
- privateKeyPassphraseHandler – Class (PrivateKeyPassphraseHandler subclass) that requests the passphrase for accessing the private key. For example: `<privateKeyPassphraseHandler>`, `<name>KeyFileHandler</name>`, `<options><password>test</password></options>`, `</privateKeyPassphraseHandler>`.
@ -622,11 +622,11 @@ Keys for server/client settings:
</openSSL>
```
## part\_log {#server_configuration_parameters-part-log}
## part_log {#server_configuration_parameters-part-log}
Logging events that are associated with [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md). For instance, adding or merging data. You can use the log to simulate merge algorithms and compare their characteristics. You can visualize the merge process.
Queries are logged in the [system.part\_log](../../operations/system-tables/part_log.md#system_tables-part-log) table, not in a separate file. You can configure the name of this table in the `table` parameter (see below).
Queries are logged in the [system.part_log](../../operations/system-tables/part_log.md#system_tables-part-log) table, not in a separate file. You can configure the name of this table in the `table` parameter (see below).
Use the following parameters to configure logging:
@ -670,7 +670,7 @@ Settings:
- `port` – Port for `endpoint`.
- `metrics` – Flag that sets to expose metrics from the [system.metrics](../../operations/system-tables/metrics.md#system_tables-metrics) table.
- `events` – Flag that sets to expose metrics from the [system.events](../../operations/system-tables/events.md#system_tables-events) table.
- `asynchronous_metrics` – Flag that sets to expose current metrics values from the [system.asynchronous\_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) table.
- `asynchronous_metrics` – Flag that sets to expose current metrics values from the [system.asynchronous_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) table.
**Example**
@ -684,11 +684,11 @@ Settings:
</prometheus>
```
## query\_log {#server_configuration_parameters-query-log}
## query_log {#server_configuration_parameters-query-log}
Setting for logging queries received with the [log\_queries=1](../../operations/settings/settings.md) setting.
Setting for logging queries received with the [log_queries=1](../../operations/settings/settings.md) setting.
Queries are logged in the [system.query\_log](../../operations/system-tables/query_log.md#system_tables-query_log) table, not in a separate file. You can change the name of the table in the `table` parameter (see below).
Queries are logged in the [system.query_log](../../operations/system-tables/query_log.md#system_tables-query_log) table, not in a separate file. You can change the name of the table in the `table` parameter (see below).
Use the following parameters to configure logging:
@ -711,11 +711,11 @@ If the table doesn’t exist, ClickHouse will create it. If the structure of the
</query_log>
```
## query\_thread\_log {#server_configuration_parameters-query_thread_log}
## query_thread_log {#server_configuration_parameters-query_thread_log}
Setting for logging threads of queries received with the [log\_query\_threads=1](../../operations/settings/settings.md#settings-log-query-threads) setting.
Setting for logging threads of queries received with the [log_query_threads=1](../../operations/settings/settings.md#settings-log-query-threads) setting.
Queries are logged in the [system.query\_thread\_log](../../operations/system-tables/query_thread_log.md#system_tables-query_thread_log) table, not in a separate file. You can change the name of the table in the `table` parameter (see below).
Queries are logged in the [system.query_thread_log](../../operations/system-tables/query_thread_log.md#system_tables-query_thread_log) table, not in a separate file. You can change the name of the table in the `table` parameter (see below).
Use the following parameters to configure logging:
@ -738,9 +738,9 @@ If the table doesn’t exist, ClickHouse will create it. If the structure of the
</query_thread_log>
```
## text\_log {#server_configuration_parameters-text_log}
## text_log {#server_configuration_parameters-text_log}
Settings for the [text\_log](../../operations/system-tables/text_log.md#system_tables-text_log) system table for logging text messages.
Settings for the [text_log](../../operations/system-tables/text_log.md#system_tables-text_log) system table for logging text messages.
Parameters:
@ -766,9 +766,9 @@ Parameters:
```
## trace\_log {#server_configuration_parameters-trace_log}
## trace_log {#server_configuration_parameters-trace_log}
Settings for the [trace\_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) system table operation.
Settings for the [trace_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) system table operation.
Parameters:
@ -789,7 +789,7 @@ The default server configuration file `config.xml` contains the following settin
</trace_log>
```
## query\_masking\_rules {#query-masking-rules}
## query_masking_rules {#query-masking-rules}
Regexp-based rules, which will be applied to queries as well as all log messages before storing them in server logs,
`system.query_log`, `system.text_log`, `system.processes` tables, and in logs sent to the client. That allows preventing
@ -820,7 +820,7 @@ The masking rules are applied to the whole query (to prevent leaks of sensitive
For distributed queries each server have to be configured separately, otherwise, subqueries passed to other
nodes will be stored without masking.
## remote\_servers {#server-settings-remote-servers}
## remote_servers {#server-settings-remote-servers}
Configuration of clusters used by the [Distributed](../../engines/table-engines/special/distributed.md) table engine and by the `cluster` table function.
@ -834,7 +834,7 @@ For the value of the `incl` attribute, see the section “[Configuration files](
**See Also**
- [skip\_unavailable\_shards](../../operations/settings/settings.md#settings-skip_unavailable_shards)
- [skip_unavailable_shards](../../operations/settings/settings.md#settings-skip_unavailable_shards)
## timezone {#server_configuration_parameters-timezone}
@ -850,7 +850,7 @@ The time zone is necessary for conversions between String and DateTime formats w
<timezone>Europe/Moscow</timezone>
```
## tcp\_port {#server_configuration_parameters-tcp_port}
## tcp_port {#server_configuration_parameters-tcp_port}
Port for communicating with clients over the TCP protocol.
@ -860,7 +860,7 @@ Port for communicating with clients over the TCP protocol.
<tcp_port>9000</tcp_port>
```
## tcp\_port\_secure {#server_configuration_parameters-tcp_port_secure}
## tcp_port_secure {#server_configuration_parameters-tcp_port_secure}
TCP port for secure communication with clients. Use it with [OpenSSL](#server_configuration_parameters-openssl) settings.
@ -874,7 +874,7 @@ Positive integer.
<tcp_port_secure>9440</tcp_port_secure>
```
## mysql\_port {#server_configuration_parameters-mysql_port}
## mysql_port {#server_configuration_parameters-mysql_port}
Port for communicating with clients over MySQL protocol.
@ -888,7 +888,7 @@ Example
<mysql_port>9004</mysql_port>
```
## tmp\_path {#tmp-path}
## tmp_path {#tmp-path}
Path to temporary data for processing large queries.
@ -901,11 +901,11 @@ Path to temporary data for processing large queries.
<tmp_path>/var/lib/clickhouse/tmp/</tmp_path>
```
## tmp\_policy {#tmp-policy}
## tmp_policy {#tmp-policy}
Policy from [storage\_configuration](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-multiple-volumes) to store temporary files.
Policy from [storage_configuration](../../engines/table-engines/mergetree-family/mergetree.md#table_engine-mergetree-multiple-volumes) to store temporary files.
If not set, [tmp\_path](#tmp-path) is used, otherwise it is ignored.
If not set, [tmp_path](#tmp-path) is used, otherwise it is ignored.
!!! note "Note"
- `move_factor` is ignored.
@ -913,11 +913,11 @@ If not set, [tmp\_path](#tmp-path) is used, otherwise it is ignored.
- `max_data_part_size_bytes` is ignored.
- Уou must have exactly one volume in that policy.
## uncompressed\_cache\_size {#server-settings-uncompressed_cache_size}
## uncompressed_cache_size {#server-settings-uncompressed_cache_size}
Cache size (in bytes) for uncompressed data used by table engines from the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md).
There is one shared cache for the server. Memory is allocated on demand. The cache is used if the option [use\_uncompressed\_cache](../../operations/settings/settings.md#setting-use_uncompressed_cache) is enabled.
There is one shared cache for the server. Memory is allocated on demand. The cache is used if the option [use_uncompressed_cache](../../operations/settings/settings.md#setting-use_uncompressed_cache) is enabled.
The uncompressed cache is advantageous for very short queries in individual cases.
@ -927,7 +927,7 @@ The uncompressed cache is advantageous for very short queries in individual case
<uncompressed_cache_size>8589934592</uncompressed_cache_size>
```
## user\_files\_path {#server_configuration_parameters-user_files_path}
## user_files_path {#server_configuration_parameters-user_files_path}
The directory with user files. Used in the table function [file()](../../sql-reference/table-functions/file.md).
@ -937,7 +937,7 @@ The directory with user files. Used in the table function [file()](../../sql-ref
<user_files_path>/var/lib/clickhouse/user_files/</user_files_path>
```
## users\_config {#users-config}
## users_config {#users-config}
Path to the file that contains:
@ -1005,13 +1005,13 @@ This section contains the following parameters:
- [Replication](../../engines/table-engines/mergetree-family/replication.md)
- [ZooKeeper Programmer’s Guide](http://zookeeper.apache.org/doc/current/zookeeperProgrammers.html)
## use\_minimalistic\_part\_header\_in\_zookeeper {#server-settings-use_minimalistic_part_header_in_zookeeper}
## use_minimalistic_part_header_in_zookeeper {#server-settings-use_minimalistic_part_header_in_zookeeper}
Storage method for data part headers in ZooKeeper.
This setting only applies to the `MergeTree` family. It can be specified:
- Globally in the [merge\_tree](#server_configuration_parameters-merge_tree) section of the `config.xml` file.
- Globally in the [merge_tree](#server_configuration_parameters-merge_tree) section of the `config.xml` file.
ClickHouse uses the setting for all the tables on the server. You can change the setting at any time. Existing tables change their behaviour when the setting changes.
@ -1033,14 +1033,14 @@ If `use_minimalistic_part_header_in_zookeeper = 1`, then [replicated](../../engi
**Default value:** 0.
## disable\_internal\_dns\_cache {#server-settings-disable-internal-dns-cache}
## disable_internal_dns_cache {#server-settings-disable-internal-dns-cache}
Disables the internal DNS cache. Recommended for operating ClickHouse in systems
with frequently changing infrastructure such as Kubernetes.
**Default value:** 0.
## dns\_cache\_update\_period {#server-settings-dns-cache-update-period}
## dns_cache_update_period {#server-settings-dns-cache-update-period}
The period of updating IP addresses stored in the ClickHouse internal DNS cache (in seconds).
The update is performed asynchronously, in a separate system thread.
@ -1049,9 +1049,9 @@ The update is performed asynchronously, in a separate system thread.
**See also**
- [background\_schedule\_pool\_size](../../operations/settings/settings.md#background_schedule_pool_size)
- [background_schedule_pool_size](../../operations/settings/settings.md#background_schedule_pool_size)
## access\_control\_path {#access_control_path}
## access_control_path {#access_control_path}
Path to a folder where a ClickHouse server stores user and role configurations created by SQL commands.

4
docs/en/operations/settings/permissions-for-queries.md
View File

@ -16,7 +16,7 @@ Queries in ClickHouse can be divided into several types:
The following settings regulate user permissions by the type of query:
- [readonly](#settings_readonly) — Restricts permissions for all types of queries except DDL queries.
- [allow\_ddl](#settings_allow_ddl) — Restricts permissions for DDL queries.
- [allow_ddl](#settings_allow_ddl) — Restricts permissions for DDL queries.
`KILL QUERY` can be performed with any settings.
@ -41,7 +41,7 @@ from changing only specific settings, for details see [constraints on settings](
Default value: 0
## allow\_ddl {#settings_allow_ddl}
## allow_ddl {#settings_allow_ddl}
Allows or denies [DDL](https://en.wikipedia.org/wiki/Data_definition_language) queries.

122
docs/en/operations/settings/query-complexity.md
View File

@ -12,8 +12,8 @@ Almost all the restrictions only apply to `SELECT`. For distributed query proces
ClickHouse checks the restrictions for data parts, not for each row. It means that you can exceed the value of restriction with the size of the data part.
Restrictions on the “maximum amount of something” can take the value 0, which means “unrestricted”.
Most restrictions also have an ‘overflow\_mode’ setting, meaning what to do when the limit is exceeded.
It can take one of two values: `throw` or `break`. Restrictions on aggregation (group\_by\_overflow\_mode) also have the value `any`.
Most restrictions also have an ‘overflow_mode’ setting, meaning what to do when the limit is exceeded.
It can take one of two values: `throw` or `break`. Restrictions on aggregation (group_by_overflow_mode) also have the value `any`.
`throw` – Throw an exception (default).
@ -21,7 +21,7 @@ It can take one of two values: `throw` or `break`. Restrictions on aggregation (
`any (only for group_by_overflow_mode)` – Continuing aggregation for the keys that got into the set, but don’t add new keys to the set.
## max\_memory\_usage {#settings_max_memory_usage}
## max_memory_usage {#settings_max_memory_usage}
The maximum amount of RAM to use for running a query on a single server.
@ -36,31 +36,31 @@ Memory usage is not monitored for the states of certain aggregate functions.
Memory usage is not fully tracked for states of the aggregate functions `min`, `max`, `any`, `anyLast`, `argMin`, `argMax` from `String` and `Array` arguments.
Memory consumption is also restricted by the parameters `max_memory_usage_for_user` and [max\_server\_memory\_usage](../../operations/server-configuration-parameters/settings.md#max_server_memory_usage).
Memory consumption is also restricted by the parameters `max_memory_usage_for_user` and [max_server_memory_usage](../../operations/server-configuration-parameters/settings.md#max_server_memory_usage).
## max\_memory\_usage\_for\_user {#max-memory-usage-for-user}
## max_memory_usage_for_user {#max-memory-usage-for-user}
The maximum amount of RAM to use for running a user’s queries on a single server.
Default values are defined in [Settings.h](https://github.com/ClickHouse/ClickHouse/blob/master/src/Core/Settings.h#L288). By default, the amount is not restricted (`max_memory_usage_for_user = 0`).
See also the description of [max\_memory\_usage](#settings_max_memory_usage).
See also the description of [max_memory_usage](#settings_max_memory_usage).
## max\_rows\_to\_read {#max-rows-to-read}
## max_rows_to_read {#max-rows-to-read}
The following restrictions can be checked on each block (instead of on each row). That is, the restrictions can be broken a little.
A maximum number of rows that can be read from a table when running a query.
## max\_bytes\_to\_read {#max-bytes-to-read}
## max_bytes_to_read {#max-bytes-to-read}
A maximum number of bytes (uncompressed data) that can be read from a table when running a query.
## read\_overflow\_mode {#read-overflow-mode}
## read_overflow_mode {#read-overflow-mode}
What to do when the volume of data read exceeds one of the limits: ‘throw’ or ‘break’. By default, throw.
## max\_rows\_to\_read_leaf {#max-rows-to-read-leaf}
## max_rows_to_read_leaf {#max-rows-to-read-leaf}
The following restrictions can be checked on each block (instead of on each row). That is, the restrictions can be broken a little.
@ -71,7 +71,7 @@ and each shard contains a table with 100 rows. Then distributed query which supp
tables with setting `max_rows_to_read=150` will fail as in total it will be 200 rows. While query
with `max_rows_to_read_leaf=150` will succeed since leaf nodes will read 100 rows at max.
## max\_bytes\_to\_read_leaf {#max-bytes-to-read-leaf}
## max_bytes_to_read_leaf {#max-bytes-to-read-leaf}
A maximum number of bytes (uncompressed data) that can be read from a local table on a leaf node when running
a distributed query. While distributed queries can issue a multiple sub-queries to each shard (leaf) - this limit will
@ -81,20 +81,20 @@ Then distributed query which suppose to read all the data from both tables with
as in total it will be 200 bytes. While query with `max_bytes_to_read_leaf=150` will succeed since leaf nodes will read
100 bytes at max.
## read\_overflow\_mode_leaf {#read-overflow-mode-leaf}
## read_overflow_mode_leaf {#read-overflow-mode-leaf}
What to do when the volume of data read exceeds one of the leaf limits: ‘throw’ or ‘break’. By default, throw.
## max\_rows\_to\_group\_by {#settings-max-rows-to-group-by}
## max_rows_to_group_by {#settings-max-rows-to-group-by}
A maximum number of unique keys received from aggregation. This setting lets you limit memory consumption when aggregating.
## group\_by\_overflow\_mode {#group-by-overflow-mode}
## group_by_overflow_mode {#group-by-overflow-mode}
What to do when the number of unique keys for aggregation exceeds the limit: ‘throw’, ‘break’, or ‘any’. By default, throw.
Using the ‘any’ value lets you run an approximation of GROUP BY. The quality of this approximation depends on the statistical nature of the data.
## max\_bytes\_before\_external\_group\_by {#settings-max_bytes_before_external_group_by}
## max_bytes_before_external_group_by {#settings-max_bytes_before_external_group_by}
Enables or disables execution of `GROUP BY` clauses in external memory. See [GROUP BY in external memory](../../sql-reference/statements/select/group-by.md#select-group-by-in-external-memory).
@ -105,31 +105,31 @@ Possible values:
Default value: 0.
## max\_rows\_to\_sort {#max-rows-to-sort}
## max_rows_to_sort {#max-rows-to-sort}
A maximum number of rows before sorting. This allows you to limit memory consumption when sorting.
## max\_bytes\_to\_sort {#max-bytes-to-sort}
## max_bytes_to_sort {#max-bytes-to-sort}
A maximum number of bytes before sorting.
## sort\_overflow\_mode {#sort-overflow-mode}
## sort_overflow_mode {#sort-overflow-mode}
What to do if the number of rows received before sorting exceeds one of the limits: ‘throw’ or ‘break’. By default, throw.
## max\_result\_rows {#setting-max_result_rows}
## max_result_rows {#setting-max_result_rows}
Limit on the number of rows in the result. Also checked for subqueries, and on remote servers when running parts of a distributed query.
## max\_result\_bytes {#max-result-bytes}
## max_result_bytes {#max-result-bytes}
Limit on the number of bytes in the result. The same as the previous setting.
## result\_overflow\_mode {#result-overflow-mode}
## result_overflow_mode {#result-overflow-mode}
What to do if the volume of the result exceeds one of the limits: ‘throw’ or ‘break’. By default, throw.
Using ‘break’ is similar to using LIMIT. `Break` interrupts execution only at the block level. This means that amount of returned rows is greater than [max\_result\_rows](#setting-max_result_rows), multiple of [max\_block\_size](../../operations/settings/settings.md#setting-max_block_size) and depends on [max\_threads](../../operations/settings/settings.md#settings-max_threads).
Using ‘break’ is similar to using LIMIT. `Break` interrupts execution only at the block level. This means that amount of returned rows is greater than [max_result_rows](#setting-max_result_rows), multiple of [max_block_size](../../operations/settings/settings.md#setting-max_block_size) and depends on [max_threads](../../operations/settings/settings.md#settings-max_threads).
Example:
@ -148,103 +148,103 @@ Result:
6666 rows in set. ...
```
## max\_execution\_time {#max-execution-time}
## max_execution_time {#max-execution-time}
Maximum query execution time in seconds.
At this time, it is not checked for one of the sorting stages, or when merging and finalizing aggregate functions.
## timeout\_overflow\_mode {#timeout-overflow-mode}
## timeout_overflow_mode {#timeout-overflow-mode}
What to do if the query is run longer than ‘max\_execution\_time’: ‘throw’ or ‘break’. By default, throw.
What to do if the query is run longer than ‘max_execution_time’: ‘throw’ or ‘break’. By default, throw.
## min\_execution\_speed {#min-execution-speed}
## min_execution_speed {#min-execution-speed}
Minimal execution speed in rows per second. Checked on every data block when ‘timeout\_before\_checking\_execution\_speed’ expires. If the execution speed is lower, an exception is thrown.
Minimal execution speed in rows per second. Checked on every data block when ‘timeout_before_checking_execution_speed’ expires. If the execution speed is lower, an exception is thrown.
## min\_execution\_speed\_bytes {#min-execution-speed-bytes}
## min_execution_speed_bytes {#min-execution-speed-bytes}
A minimum number of execution bytes per second. Checked on every data block when ‘timeout\_before\_checking\_execution\_speed’ expires. If the execution speed is lower, an exception is thrown.
A minimum number of execution bytes per second. Checked on every data block when ‘timeout_before_checking_execution_speed’ expires. If the execution speed is lower, an exception is thrown.
## max\_execution\_speed {#max-execution-speed}
## max_execution_speed {#max-execution-speed}
A maximum number of execution rows per second. Checked on every data block when ‘timeout\_before\_checking\_execution\_speed’ expires. If the execution speed is high, the execution speed will be reduced.
A maximum number of execution rows per second. Checked on every data block when ‘timeout_before_checking_execution_speed’ expires. If the execution speed is high, the execution speed will be reduced.
## max\_execution\_speed\_bytes {#max-execution-speed-bytes}
## max_execution_speed_bytes {#max-execution-speed-bytes}
A maximum number of execution bytes per second. Checked on every data block when ‘timeout\_before\_checking\_execution\_speed’ expires. If the execution speed is high, the execution speed will be reduced.
A maximum number of execution bytes per second. Checked on every data block when ‘timeout_before_checking_execution_speed’ expires. If the execution speed is high, the execution speed will be reduced.
## timeout\_before\_checking\_execution\_speed {#timeout-before-checking-execution-speed}
## timeout_before_checking_execution_speed {#timeout-before-checking-execution-speed}
Checks that execution speed is not too slow (no less than ‘min\_execution\_speed’), after the specified time in seconds has expired.
Checks that execution speed is not too slow (no less than ‘min_execution_speed’), after the specified time in seconds has expired.
## max\_columns\_to\_read {#max-columns-to-read}
## max_columns_to_read {#max-columns-to-read}
A maximum number of columns that can be read from a table in a single query. If a query requires reading a greater number of columns, it throws an exception.
## max\_temporary\_columns {#max-temporary-columns}
## max_temporary_columns {#max-temporary-columns}
A maximum number of temporary columns that must be kept in RAM at the same time when running a query, including constant columns. If there are more temporary columns than this, it throws an exception.
## max\_temporary\_non\_const\_columns {#max-temporary-non-const-columns}
## max_temporary_non_const_columns {#max-temporary-non-const-columns}
The same thing as ‘max\_temporary\_columns’, but without counting constant columns.
The same thing as ‘max_temporary_columns’, but without counting constant columns.
Note that constant columns are formed fairly often when running a query, but they require approximately zero computing resources.
## max\_subquery\_depth {#max-subquery-depth}
## max_subquery_depth {#max-subquery-depth}
Maximum nesting depth of subqueries. If subqueries are deeper, an exception is thrown. By default, 100.
## max\_pipeline\_depth {#max-pipeline-depth}
## max_pipeline_depth {#max-pipeline-depth}
Maximum pipeline depth. Corresponds to the number of transformations that each data block goes through during query processing. Counted within the limits of a single server. If the pipeline depth is greater, an exception is thrown. By default, 1000.
## max\_ast\_depth {#max-ast-depth}
## max_ast_depth {#max-ast-depth}
Maximum nesting depth of a query syntactic tree. If exceeded, an exception is thrown.
At this time, it isn’t checked during parsing, but only after parsing the query. That is, a syntactic tree that is too deep can be created during parsing, but the query will fail. By default, 1000.
## max\_ast\_elements {#max-ast-elements}
## max_ast_elements {#max-ast-elements}
A maximum number of elements in a query syntactic tree. If exceeded, an exception is thrown.
In the same way as the previous setting, it is checked only after parsing the query. By default, 50,000.
## max\_rows\_in\_set {#max-rows-in-set}
## max_rows_in_set {#max-rows-in-set}
A maximum number of rows for a data set in the IN clause created from a subquery.
## max\_bytes\_in\_set {#max-bytes-in-set}
## max_bytes_in_set {#max-bytes-in-set}
A maximum number of bytes (uncompressed data) used by a set in the IN clause created from a subquery.
## set\_overflow\_mode {#set-overflow-mode}
## set_overflow_mode {#set-overflow-mode}
What to do when the amount of data exceeds one of the limits: ‘throw’ or ‘break’. By default, throw.
## max\_rows\_in\_distinct {#max-rows-in-distinct}
## max_rows_in_distinct {#max-rows-in-distinct}
A maximum number of different rows when using DISTINCT.
## max\_bytes\_in\_distinct {#max-bytes-in-distinct}
## max_bytes_in_distinct {#max-bytes-in-distinct}
A maximum number of bytes used by a hash table when using DISTINCT.
## distinct\_overflow\_mode {#distinct-overflow-mode}
## distinct_overflow_mode {#distinct-overflow-mode}
What to do when the amount of data exceeds one of the limits: ‘throw’ or ‘break’. By default, throw.
## max\_rows\_to\_transfer {#max-rows-to-transfer}
## max_rows_to_transfer {#max-rows-to-transfer}
A maximum number of rows that can be passed to a remote server or saved in a temporary table when using GLOBAL IN.
## max\_bytes\_to\_transfer {#max-bytes-to-transfer}
## max_bytes_to_transfer {#max-bytes-to-transfer}
A maximum number of bytes (uncompressed data) that can be passed to a remote server or saved in a temporary table when using GLOBAL IN.
## transfer\_overflow\_mode {#transfer-overflow-mode}
## transfer_overflow_mode {#transfer-overflow-mode}
What to do when the amount of data exceeds one of the limits: ‘throw’ or ‘break’. By default, throw.
## max\_rows\_in\_join {#settings-max_rows_in_join}
## max_rows_in_join {#settings-max_rows_in_join}
Limits the number of rows in the hash table that is used when joining tables.
@ -252,7 +252,7 @@ This settings applies to [SELECT … JOIN](../../sql-reference/statements/select
If a query contains multiple joins, ClickHouse checks this setting for every intermediate result.
ClickHouse can proceed with different actions when the limit is reached. Use the [join\_overflow\_mode](#settings-join_overflow_mode) setting to choose the action.
ClickHouse can proceed with different actions when the limit is reached. Use the [join_overflow_mode](#settings-join_overflow_mode) setting to choose the action.
Possible values:
@ -261,7 +261,7 @@ Possible values:
Default value: 0.
## max\_bytes\_in\_join {#settings-max_bytes_in_join}
## max_bytes_in_join {#settings-max_bytes_in_join}
Limits the size in bytes of the hash table used when joining tables.
@ -269,7 +269,7 @@ This settings applies to [SELECT … JOIN](../../sql-reference/statements/select
If the query contains joins, ClickHouse checks this setting for every intermediate result.
ClickHouse can proceed with different actions when the limit is reached. Use [join\_overflow\_mode](#settings-join_overflow_mode) settings to choose the action.
ClickHouse can proceed with different actions when the limit is reached. Use [join_overflow_mode](#settings-join_overflow_mode) settings to choose the action.
Possible values:
@ -278,12 +278,12 @@ Possible values:
Default value: 0.
## join\_overflow\_mode {#settings-join_overflow_mode}
## join_overflow_mode {#settings-join_overflow_mode}
Defines what action ClickHouse performs when any of the following join limits is reached:
- [max\_bytes\_in\_join](#settings-max_bytes_in_join)
- [max\_rows\_in\_join](#settings-max_rows_in_join)
- [max_bytes_in_join](#settings-max_bytes_in_join)
- [max_rows_in_join](#settings-max_rows_in_join)
Possible values:
@ -297,7 +297,7 @@ Default value: `THROW`.
- [JOIN clause](../../sql-reference/statements/select/join.md#select-join)
- [Join table engine](../../engines/table-engines/special/join.md)
## max\_partitions\_per\_insert\_block {#max-partitions-per-insert-block}
## max_partitions_per_insert_block {#max-partitions-per-insert-block}
Limits the maximum number of partitions in a single inserted block.
@ -310,6 +310,6 @@ Default value: 100.
When inserting data, ClickHouse calculates the number of partitions in the inserted block. If the number of partitions is more than `max_partitions_per_insert_block`, ClickHouse throws an exception with the following text:
> “Too many partitions for single INSERT block (more than” + toString(max\_parts) + “). The limit is controlled by ‘max\_partitions\_per\_insert\_block’ setting. A large number of partitions is a common misconception. It will lead to severe negative performance impact, including slow server startup, slow INSERT queries and slow SELECT queries. Recommended total number of partitions for a table is under 1000..10000. Please note, that partitioning is not intended to speed up SELECT queries (ORDER BY key is sufficient to make range queries fast). Partitions are intended for data manipulation (DROP PARTITION, etc).”
> “Too many partitions for single INSERT block (more than” + toString(max_parts) + “). The limit is controlled by ‘max_partitions_per_insert_block’ setting. A large number of partitions is a common misconception. It will lead to severe negative performance impact, including slow server startup, slow INSERT queries and slow SELECT queries. Recommended total number of partitions for a table is under 1000..10000. Please note, that partitioning is not intended to speed up SELECT queries (ORDER BY key is sufficient to make range queries fast). Partitions are intended for data manipulation (DROP PARTITION, etc).”
[Original article](https://clickhouse.tech/docs/en/operations/settings/query_complexity/) <!--hide-->

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@ -41,7 +41,7 @@ Structure of the `users` section:
</users>
```
### user\_name/password {#user-namepassword}
### user_name/password {#user-namepassword}
Password can be specified in plaintext or in SHA256 (hex format).
@ -73,7 +73,7 @@ Password can be specified in plaintext or in SHA256 (hex format).
The first line of the result is the password. The second line is the corresponding double SHA1 hash.
### access\_management {#access_management-user-setting}
### access_management {#access_management-user-setting}
This setting enables or disables using of SQL-driven [access control and account management](../../operations/access-rights.md#access-control) for the user.
@ -84,7 +84,7 @@ Possible values:
Default value: 0.
### user\_name/networks {#user-namenetworks}
### user_name/networks {#user-namenetworks}
List of networks from which the user can connect to the ClickHouse server.
@ -126,18 +126,18 @@ To open access only from localhost, specify:
<ip>127.0.0.1</ip>
```
### user\_name/profile {#user-nameprofile}
### user_name/profile {#user-nameprofile}
You can assign a settings profile for the user. Settings profiles are configured in a separate section of the `users.xml` file. For more information, see [Profiles of Settings](../../operations/settings/settings-profiles.md).
### user\_name/quota {#user-namequota}
### user_name/quota {#user-namequota}
Quotas allow you to track or limit resource usage over a period of time. Quotas are configured in the `quotas`
section of the `users.xml` configuration file.
You can assign a quotas set for the user. For a detailed description of quotas configuration, see [Quotas](../../operations/quotas.md#quotas).
### user\_name/databases {#user-namedatabases}
### user_name/databases {#user-namedatabases}
In this section, you can you can limit rows that are returned by ClickHouse for `SELECT` queries made by the current user, thus implementing basic row-level security.

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@ -33,6 +33,6 @@ SELECT * FROM system.asynchronous_metrics LIMIT 10
- [Monitoring](../../operations/monitoring.md) — Base concepts of ClickHouse monitoring.
- [system.metrics](../../operations/system-tables/metrics.md#system_tables-metrics) — Contains instantly calculated metrics.
- [system.events](../../operations/system-tables/events.md#system_tables-events) — Contains a number of events that have occurred.
- [system.metric\_log](../../operations/system-tables/metric_log.md#system_tables-metric_log) — Contains a history of metrics values from tables `system.metrics` и `system.events`.
- [system.metric_log](../../operations/system-tables/metric_log.md#system_tables-metric_log) — Contains a history of metrics values from tables `system.metrics` и `system.events`.
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/asynchronous_metrics) <!--hide-->

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@ -20,7 +20,7 @@ Please note that `errors_count` is updated once per query to the cluster, but `e
**See also**
- [Table engine Distributed](../../engines/table-engines/special/distributed.md)
- [distributed\_replica\_error\_cap setting](../../operations/settings/settings.md#settings-distributed_replica_error_cap)
- [distributed\_replica\_error\_half\_life setting](../../operations/settings/settings.md#settings-distributed_replica_error_half_life)
- [distributed_replica_error_cap setting](../../operations/settings/settings.md#settings-distributed_replica_error_cap)
- [distributed_replica_error_half_life setting](../../operations/settings/settings.md#settings-distributed_replica_error_half_life)
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/clusters) <!--hide-->

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@ -26,9 +26,9 @@ SELECT * FROM system.events LIMIT 5
**See Also**
- [system.asynchronous\_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) — Contains periodically calculated metrics.
- [system.asynchronous_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) — Contains periodically calculated metrics.
- [system.metrics](../../operations/system-tables/metrics.md#system_tables-metrics) — Contains instantly calculated metrics.
- [system.metric\_log](../../operations/system-tables/metric_log.md#system_tables-metric_log) — Contains a history of metrics values from tables `system.metrics` и `system.events`.
- [system.metric_log](../../operations/system-tables/metric_log.md#system_tables-metric_log) — Contains a history of metrics values from tables `system.metrics` и `system.events`.
- [Monitoring](../../operations/monitoring.md) — Base concepts of ClickHouse monitoring.
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/events) <!--hide-->

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@ -1,6 +1,6 @@
# system.graphite_retentions {#system-graphite-retentions}
Contains information about parameters [graphite\_rollup](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-graphite) which are used in tables with [\*GraphiteMergeTree](../../engines/table-engines/mergetree-family/graphitemergetree.md) engines.
Contains information about parameters [graphite_rollup](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-graphite) which are used in tables with [\*GraphiteMergeTree](../../engines/table-engines/mergetree-family/graphitemergetree.md) engines.
Columns:

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@ -20,7 +20,7 @@ System tables:
Most of system tables store their data in RAM. A ClickHouse server creates such system tables at the start.
Unlike other system tables, the system tables [metric\_log](../../operations/system-tables/metric_log.md#system_tables-metric_log), [query\_log](../../operations/system-tables/query_log.md#system_tables-query_log), [query\_thread\_log](../../operations/system-tables/query_thread_log.md#system_tables-query_thread_log), [trace\_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) are served by [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) table engine and store their data in a storage filesystem. If you remove a table from a filesystem, the ClickHouse server creates the empty one again at the time of the next data writing. If system table schema changed in a new release, then ClickHouse renames the current table and creates a new one.
Unlike other system tables, the system tables [metric_log](../../operations/system-tables/metric_log.md#system_tables-metric_log), [query_log](../../operations/system-tables/query_log.md#system_tables-query_log), [query_thread_log](../../operations/system-tables/query_thread_log.md#system_tables-query_thread_log), [trace_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) are served by [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) table engine and store their data in a storage filesystem. If you remove a table from a filesystem, the ClickHouse server creates the empty one again at the time of the next data writing. If system table schema changed in a new release, then ClickHouse renames the current table and creates a new one.
By default, table growth is unlimited. To control a size of a table, you can use [TTL](../../sql-reference/statements/alter/ttl.md#manipulations-with-table-ttl) settings for removing outdated log records. Also you can use the partitioning feature of `MergeTree`-engine tables.

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@ -49,7 +49,7 @@ CurrentMetric_DistributedFilesToInsert: 0
**See also**
- [system.asynchronous\_metrics](../../operations/system-tables/asynchronous_metrics.md) — Contains periodically calculated metrics.
- [system.asynchronous_metrics](../../operations/system-tables/asynchronous_metrics.md) — Contains periodically calculated metrics.
- [system.events](../../operations/system-tables/events.md#system_tables-events) — Contains a number of events that occurred.
- [system.metrics](../../operations/system-tables/metrics.md) — Contains instantly calculated metrics.
- [Monitoring](../../operations/monitoring.md) — Base concepts of ClickHouse monitoring.

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@ -33,9 +33,9 @@ SELECT * FROM system.metrics LIMIT 10
**See Also**
- [system.asynchronous\_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) — Contains periodically calculated metrics.
- [system.asynchronous_metrics](../../operations/system-tables/asynchronous_metrics.md#system_tables-asynchronous_metrics) — Contains periodically calculated metrics.
- [system.events](../../operations/system-tables/events.md#system_tables-events) — Contains a number of events that occurred.
- [system.metric\_log](../../operations/system-tables/metric_log.md#system_tables-metric_log) — Contains a history of metrics values from tables `system.metrics` и `system.events`.
- [system.metric_log](../../operations/system-tables/metric_log.md#system_tables-metric_log) — Contains a history of metrics values from tables `system.metrics` и `system.events`.
- [Monitoring](../../operations/monitoring.md) — Base concepts of ClickHouse monitoring.
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/metrics) <!--hide-->

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@ -1,6 +1,6 @@
# system.part_log {#system_tables-part-log}
The `system.part_log` table is created only if the [part\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-part-log) server setting is specified.
The `system.part_log` table is created only if the [part_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-part-log) server setting is specified.
This table contains information about events that occurred with [data parts](../../engines/table-engines/mergetree-family/custom-partitioning-key.md) in the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md) family tables, such as adding or merging data.

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@ -10,7 +10,7 @@ Columns:
- `rows_read` (UInt64) – The number of rows read from the table. For distributed processing, on the requestor server, this is the total for all remote servers.
- `bytes_read` (UInt64) – The number of uncompressed bytes read from the table. For distributed processing, on the requestor server, this is the total for all remote servers.
- `total_rows_approx` (UInt64) – The approximation of the total number of rows that should be read. For distributed processing, on the requestor server, this is the total for all remote servers. It can be updated during request processing, when new sources to process become known.
- `memory_usage` (UInt64) – Amount of RAM the request uses. It might not include some types of dedicated memory. See the [max\_memory\_usage](../../operations/settings/query-complexity.md#settings_max_memory_usage) setting.
- `memory_usage` (UInt64) – Amount of RAM the request uses. It might not include some types of dedicated memory. See the [max_memory_usage](../../operations/settings/query-complexity.md#settings_max_memory_usage) setting.
- `query` (String) – The query text. For `INSERT`, it doesn’t include the data to insert.
- `query_id` (String) – Query ID, if defined.

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@ -5,11 +5,11 @@ Contains information about executed queries, for example, start time, duration o
!!! note "Note"
This table doesn’t contain the ingested data for `INSERT` queries.
You can change settings of queries logging in the [query\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query-log) section of the server configuration.
You can change settings of queries logging in the [query_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query-log) section of the server configuration.
You can disable queries logging by setting [log\_queries = 0](../../operations/settings/settings.md#settings-log-queries). We don’t recommend to turn off logging because information in this table is important for solving issues.
You can disable queries logging by setting [log_queries = 0](../../operations/settings/settings.md#settings-log-queries). We don’t recommend to turn off logging because information in this table is important for solving issues.
The flushing period of data is set in `flush_interval_milliseconds` parameter of the [query\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query-log) server settings section. To force flushing, use the [SYSTEM FLUSH LOGS](../../sql-reference/statements/system.md#query_language-system-flush_logs) query.
The flushing period of data is set in `flush_interval_milliseconds` parameter of the [query_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query-log) server settings section. To force flushing, use the [SYSTEM FLUSH LOGS](../../sql-reference/statements/system.md#query_language-system-flush_logs) query.
ClickHouse doesn’t delete data from the table automatically. See [Introduction](../../operations/system-tables/index.md#system-tables-introduction) for more details.
@ -140,7 +140,7 @@ Settings.Values: ['0','random','1','10000000000','1']
**See Also**
- [system.query\_thread\_log](../../operations/system-tables/query_thread_log.md#system_tables-query_thread_log) — This table contains information about each query execution thread.
- [system.query_thread_log](../../operations/system-tables/query_thread_log.md#system_tables-query_thread_log) — This table contains information about each query execution thread.
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/query_log) <!--hide-->

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@ -4,10 +4,10 @@ Contains information about threads which execute queries, for example, thread na
To start logging:
1. Configure parameters in the [query\_thread\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query_thread_log) section.
2. Set [log\_query\_threads](../../operations/settings/settings.md#settings-log-query-threads) to 1.
1. Configure parameters in the [query_thread_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query_thread_log) section.
2. Set [log_query_threads](../../operations/settings/settings.md#settings-log-query-threads) to 1.
The flushing period of data is set in `flush_interval_milliseconds` parameter of the [query\_thread\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query_thread_log) server settings section. To force flushing, use the [SYSTEM FLUSH LOGS](../../sql-reference/statements/system.md#query_language-system-flush_logs) query.
The flushing period of data is set in `flush_interval_milliseconds` parameter of the [query_thread_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-query_thread_log) server settings section. To force flushing, use the [SYSTEM FLUSH LOGS](../../sql-reference/statements/system.md#query_language-system-flush_logs) query.
ClickHouse doesn’t delete data from the table automatically. See [Introduction](../../operations/system-tables/index.md#system-tables-introduction) for more details.
@ -113,6 +113,6 @@ ProfileEvents.Values: [1,1,11,11,591,148,3,71,29,6533808,1,11,72,18,47,
**See Also**
- [system.query\_log](../../operations/system-tables/query_log.md#system_tables-query_log) — Description of the `query_log` system table which contains common information about queries execution.
- [system.query_log](../../operations/system-tables/query_log.md#system_tables-query_log) — Description of the `query_log` system table which contains common information about queries execution.
[Original article](https://clickhouse.tech/docs/en/operations/system_tables/query_thread_log) <!--hide-->

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@ -63,7 +63,7 @@ Columns:
- `parts_to_check` (`UInt32`) - The number of data parts in the queue for verification. A part is put in the verification queue if there is suspicion that it might be damaged.
- `zookeeper_path` (`String`) - Path to table data in ZooKeeper.
- `replica_name` (`String`) - Replica name in ZooKeeper. Different replicas of the same table have different names.
- `replica_path` (`String`) - Path to replica data in ZooKeeper. The same as concatenating ‘zookeeper\_path/replicas/replica\_path’.
- `replica_path` (`String`) - Path to replica data in ZooKeeper. The same as concatenating ‘zookeeper_path/replicas/replica_path’.
- `columns_version` (`Int32`) - Version number of the table structure. Indicates how many times ALTER was performed. If replicas have different versions, it means some replicas haven’t made all of the ALTERs yet.
- `queue_size` (`UInt32`) - Size of the queue for operations waiting to be performed. Operations include inserting blocks of data, merges, and certain other actions. It usually coincides with `future_parts`.
- `inserts_in_queue` (`UInt32`) - Number of inserts of blocks of data that need to be made. Insertions are usually replicated fairly quickly. If this number is large, it means something is wrong.
@ -84,7 +84,7 @@ The next 4 columns have a non-zero value only where there is an active session w
- `active_replicas` (`UInt8`) - The number of replicas of this table that have a session in ZooKeeper (i.e., the number of functioning replicas).
If you request all the columns, the table may work a bit slowly, since several reads from ZooKeeper are made for each row.
If you don’t request the last 4 columns (log\_max\_index, log\_pointer, total\_replicas, active\_replicas), the table works quickly.
If you don’t request the last 4 columns (log_max_index, log_pointer, total_replicas, active_replicas), the table works quickly.
For example, you can check that everything is working correctly like this:

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@ -1,4 +1,4 @@
# system.text\_log {#system_tables-text_log}
# system.text_log {#system_tables-text_log}
Contains logging entries. Logging level which goes to this table can be limited with `text_log.level` server setting.

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@ -2,7 +2,7 @@
Contains stack traces collected by the sampling query profiler.
ClickHouse creates this table when the [trace\_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-trace_log) server configuration section is set. Also the [query\_profiler\_real\_time\_period\_ns](../../operations/settings/settings.md#query_profiler_real_time_period_ns) and [query\_profiler\_cpu\_time\_period\_ns](../../operations/settings/settings.md#query_profiler_cpu_time_period_ns) settings should be set.
ClickHouse creates this table when the [trace_log](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-trace_log) server configuration section is set. Also the [query_profiler_real_time_period_ns](../../operations/settings/settings.md#query_profiler_real_time_period_ns) and [query_profiler_cpu_time_period_ns](../../operations/settings/settings.md#query_profiler_cpu_time_period_ns) settings should be set.
To analyze logs, use the `addressToLine`, `addressToSymbol` and `demangle` introspection functions.
@ -27,7 +27,7 @@ Columns:
- `thread_number` ([UInt32](../../sql-reference/data-types/int-uint.md)) — Thread identifier.
- `query_id` ([String](../../sql-reference/data-types/string.md)) — Query identifier that can be used to get details about a query that was running from the [query\_log](#system_tables-query_log) system table.
- `query_id` ([String](../../sql-reference/data-types/string.md)) — Query identifier that can be used to get details about a query that was running from the [query_log](#system_tables-query_log) system table.
- `trace` ([Array(UInt64)](../../sql-reference/data-types/array.md)) — Stack trace at the moment of sampling. Each element is a virtual memory address inside ClickHouse server process.

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@ -57,7 +57,7 @@ When creating RAID-10, select the `far` layout.
If your budget allows, choose RAID-10.
If you have more than 4 disks, use RAID-6 (preferred) or RAID-50, instead of RAID-5.
When using RAID-5, RAID-6 or RAID-50, always increase stripe\_cache\_size, since the default value is usually not the best choice.
When using RAID-5, RAID-6 or RAID-50, always increase stripe_cache_size, since the default value is usually not the best choice.
``` bash
$ echo 4096 | sudo tee /sys/block/md2/md/stripe_cache_size

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@ -103,7 +103,7 @@ Check:
- Endpoint settings.
Check [listen\_host](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-listen_host) and [tcp\_port](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-tcp_port) settings.
Check [listen_host](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-listen_host) and [tcp_port](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-tcp_port) settings.
ClickHouse server accepts localhost connections only by default.
@ -115,7 +115,7 @@ Check:
Check:
- The [tcp\_port\_secure](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-tcp_port_secure) setting.
- The [tcp_port_secure](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-tcp_port_secure) setting.
- Settings for [SSL certificates](../operations/server-configuration-parameters/settings.md#server_configuration_parameters-openssl).
Use proper parameters while connecting. For example, use the `port_secure` parameter with `clickhouse_client`.

2
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@ -492,6 +492,6 @@ Solution: Write in the GROUP BY query SearchPhrase HAVING uniqUpTo(4)(UserID) >=
[Original article](https://clickhouse.tech/docs/en/query_language/agg_functions/parametric_functions/) <!--hide-->
## sumMapFiltered(keys\_to\_keep)(keys, values) {#summapfilteredkeys-to-keepkeys-values}
## sumMapFiltered(keys_to_keep)(keys, values) {#summapfilteredkeys-to-keepkeys-values}
Same behavior as [sumMap](../../sql-reference/aggregate-functions/reference/summap.md#agg_functions-summap) except that an array of keys is passed as a parameter. This can be especially useful when working with a high cardinality of keys.

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@ -26,7 +26,7 @@ In both cases the type of the returned value is [UInt64](../../../sql-reference/
**Details**
ClickHouse supports the `COUNT(DISTINCT ...)` syntax. The behavior of this construction depends on the [count\_distinct\_implementation](../../../operations/settings/settings.md#settings-count_distinct_implementation) setting. It defines which of the [uniq\*](../../../sql-reference/aggregate-functions/reference/uniq.md#agg_function-uniq) functions is used to perform the operation. The default is the [uniqExact](../../../sql-reference/aggregate-functions/reference/uniqexact.md#agg_function-uniqexact) function.
ClickHouse supports the `COUNT(DISTINCT ...)` syntax. The behavior of this construction depends on the [count_distinct_implementation](../../../operations/settings/settings.md#settings-count_distinct_implementation) setting. It defines which of the [uniq\*](../../../sql-reference/aggregate-functions/reference/uniq.md#agg_function-uniq) functions is used to perform the operation. The default is the [uniqExact](../../../sql-reference/aggregate-functions/reference/uniqexact.md#agg_function-uniqexact) function.
The `SELECT count() FROM table` query is not optimized, because the number of entries in the table is not stored separately. It chooses a small column from the table and counts the number of values in it.

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@ -34,8 +34,8 @@ The following table lists cases when query feature works in ClickHouse, but beha
| E021-01 | CHARACTER data type | No{.text-danger} | |
| E021-02 | CHARACTER VARYING data type | No{.text-danger} | `String` behaves similarly, but without length limit in parentheses |
| E021-03 | Character literals | Partial{.text-warning} | No automatic concatenation of consecutive literals and character set support |
| E021-04 | CHARACTER\_LENGTH function | Partial{.text-warning} | No `USING` clause |
| E021-05 | OCTET\_LENGTH function | No{.text-danger} | `LENGTH` behaves similarly |
| E021-04 | CHARACTER_LENGTH function | Partial{.text-warning} | No `USING` clause |
| E021-05 | OCTET_LENGTH function | No{.text-danger} | `LENGTH` behaves similarly |
| E021-06 | SUBSTRING | Partial{.text-warning} | No support for `SIMILAR` and `ESCAPE` clauses, no `SUBSTRING_REGEX` variant |
| E021-07 | Character concatenation | Partial{.text-warning} | No `COLLATE` clause |
| E021-08 | UPPER and LOWER functions | Yes{.text-success} | |
@ -152,7 +152,7 @@ The following table lists cases when query feature works in ClickHouse, but beha
| F051-03 | TIMESTAMP data type (including support of TIMESTAMP literal) with fractional seconds precision of at least 0 and 6 | No{.text-danger} | `DateTime64` time provides similar functionality |
| F051-04 | Comparison predicate on DATE, TIME, and TIMESTAMP data types | Partial{.text-warning} | Only one data type available |
| F051-05 | Explicit CAST between datetime types and character string types | Yes{.text-success} | |
| F051-06 | CURRENT\_DATE | No{.text-danger} | `today()` is similar |
| F051-06 | CURRENT_DATE | No{.text-danger} | `today()` is similar |
| F051-07 | LOCALTIME | No{.text-danger} | `now()` is similar |
| F051-08 | LOCALTIMESTAMP | No{.text-danger} | |
| **F081** | **UNION and EXCEPT in views** | **Partial**{.text-warning} | |

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@ -27,9 +27,9 @@ You can explicitly set a time zone for `DateTime`-type columns when creating a t
The [clickhouse-client](../../interfaces/cli.md) applies the server time zone by default if a time zone isn’t explicitly set when initializing the data type. To use the client time zone, run `clickhouse-client` with the `--use_client_time_zone` parameter.
ClickHouse outputs values in `YYYY-MM-DD hh:mm:ss` text format by default. You can change the output with the [formatDateTime](../../sql-reference/functions/date-time-functions.md#formatdatetime) function.
ClickHouse outputs values depending on the value of the [date\_time\_output\_format](../../operations/settings/settings.md#settings-date_time_output_format) setting. `YYYY-MM-DD hh:mm:ss` text format by default. Additionaly you can change the output with the [formatDateTime](../../sql-reference/functions/date-time-functions.md#formatdatetime) function.
When inserting data into ClickHouse, you can use different formats of date and time strings, depending on the value of the [date\_time\_input\_format](../../operations/settings/settings.md#settings-date_time_input_format) setting.
When inserting data into ClickHouse, you can use different formats of date and time strings, depending on the value of the [date_time_input_format](../../operations/settings/settings.md#settings-date_time_input_format) setting.
## Examples {#examples}
@ -120,6 +120,7 @@ FROM dt
- [Functions for working with dates and times](../../sql-reference/functions/date-time-functions.md)
- [Functions for working with arrays](../../sql-reference/functions/array-functions.md)
- [The `date_time_input_format` setting](../../operations/settings/settings.md#settings-date_time_input_format)
- [The `date_time_output_format` setting](../../operations/settings/settings.md#settings-date_time_output_format)
- [The `timezone` server configuration parameter](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-timezone)
- [Operators for working with dates and times](../../sql-reference/operators/index.md#operators-datetime)
- [The `Date` data type](../../sql-reference/data-types/date.md)

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@ -96,6 +96,7 @@ FROM dt
- [Functions for working with dates and times](../../sql-reference/functions/date-time-functions.md)
- [Functions for working with arrays](../../sql-reference/functions/array-functions.md)
- [The `date_time_input_format` setting](../../operations/settings/settings.md#settings-date_time_input_format)
- [The `date_time_output_format` setting](../../operations/settings/settings.md#settings-date_time_output_format)
- [The `timezone` server configuration parameter](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-timezone)
- [Operators for working with dates and times](../../sql-reference/operators/index.md#operators-datetime)
- [`Date` data type](../../sql-reference/data-types/date.md)

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@ -20,7 +20,7 @@ The `FixedString` type is efficient when data has the length of precisely `N` by
Examples of the values that can be efficiently stored in `FixedString`-typed columns:
- The binary representation of IP addresses (`FixedString(16)` for IPv6).
- Language codes (ru\_RU, en\_US … ).
- Language codes (ru_RU, en_US … ).
- Currency codes (USD, RUB … ).
- Binary representation of hashes (`FixedString(16)` for MD5, `FixedString(32)` for SHA256).

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@ -10,6 +10,6 @@ ClickHouse can store various kinds of data in table cells.
This section describes the supported data types and special considerations for using and/or implementing them if any.
You can check whether data type name is case-sensitive in the [system.data\_type\_families](../../operations/system-tables/data_type_families.md#system_tables-data_type_families) table.
You can check whether data type name is case-sensitive in the [system.data_type_families](../../operations/system-tables/data_type_families.md#system_tables-data_type_families) table.
[Original article](https://clickhouse.tech/docs/en/data_types/) <!--hide-->

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@ -15,7 +15,7 @@ LowCardinality(data_type)
**Parameters**
- `data_type` — [String](../../sql-reference/data-types/string.md), [FixedString](../../sql-reference/data-types/fixedstring.md), [Date](../../sql-reference/data-types/date.md), [DateTime](../../sql-reference/data-types/datetime.md), and numbers excepting [Decimal](../../sql-reference/data-types/decimal.md). `LowCardinality` is not efficient for some data types, see the [allow\_suspicious\_low\_cardinality\_types](../../operations/settings/settings.md#allow_suspicious_low_cardinality_types) setting description.
- `data_type` — [String](../../sql-reference/data-types/string.md), [FixedString](../../sql-reference/data-types/fixedstring.md), [Date](../../sql-reference/data-types/date.md), [DateTime](../../sql-reference/data-types/datetime.md), and numbers excepting [Decimal](../../sql-reference/data-types/decimal.md). `LowCardinality` is not efficient for some data types, see the [allow_suspicious_low_cardinality_types](../../operations/settings/settings.md#allow_suspicious_low_cardinality_types) setting description.
## Description {#lowcardinality-dscr}
@ -43,10 +43,10 @@ ORDER BY id
Settings:
- [low\_cardinality\_max\_dictionary\_size](../../operations/settings/settings.md#low_cardinality_max_dictionary_size)
- [low\_cardinality\_use\_single\_dictionary\_for\_part](../../operations/settings/settings.md#low_cardinality_use_single_dictionary_for_part)
- [low\_cardinality\_allow\_in\_native\_format](../../operations/settings/settings.md#low_cardinality_allow_in_native_format)
- [allow\_suspicious\_low\_cardinality\_types](../../operations/settings/settings.md#allow_suspicious_low_cardinality_types)
- [low_cardinality_max_dictionary_size](../../operations/settings/settings.md#low_cardinality_max_dictionary_size)
- [low_cardinality_use_single_dictionary_for_part](../../operations/settings/settings.md#low_cardinality_use_single_dictionary_for_part)
- [low_cardinality_allow_in_native_format](../../operations/settings/settings.md#low_cardinality_allow_in_native_format)
- [allow_suspicious_low_cardinality_types](../../operations/settings/settings.md#allow_suspicious_low_cardinality_types)
Functions:

2
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@ -25,7 +25,7 @@ Look at the following hierarchical structure:
This hierarchy can be expressed as the following dictionary table.
| region\_id | parent\_region | region\_name |
| region_id | parent_region | region_name |
|------------|----------------|---------------|
| 1 | 0 | Russia |
| 2 | 1 | Moscow |

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@ -7,7 +7,7 @@ toc_title: Storing Dictionaries in Memory
There are a variety of ways to store dictionaries in memory.
We recommend [flat](#flat), [hashed](#dicts-external_dicts_dict_layout-hashed) and [complex\_key\_hashed](#complex-key-hashed). which provide optimal processing speed.
We recommend [flat](#flat), [hashed](#dicts-external_dicts_dict_layout-hashed) and [complex_key_hashed](#complex-key-hashed). which provide optimal processing speed.
Caching is not recommended because of potentially poor performance and difficulties in selecting optimal parameters. Read more in the section “[cache](#cache)”.
@ -52,16 +52,16 @@ LAYOUT(LAYOUT_TYPE(param value)) -- layout settings
- [flat](#flat)
- [hashed](#dicts-external_dicts_dict_layout-hashed)
- [sparse\_hashed](#dicts-external_dicts_dict_layout-sparse_hashed)
- [sparse_hashed](#dicts-external_dicts_dict_layout-sparse_hashed)
- [cache](#cache)
- [ssd\_cache](#ssd-cache)
- [ssd_cache](#ssd-cache)
- [direct](#direct)
- [range\_hashed](#range-hashed)
- [complex\_key\_hashed](#complex-key-hashed)
- [complex\_key\_cache](#complex-key-cache)
- [ssd\_complex\_key\_cache](#ssd-cache)
- [complex\_key\_direct](#complex-key-direct)
- [ip\_trie](#ip-trie)
- [range_hashed](#range-hashed)
- [complex_key_hashed](#complex-key-hashed)
- [complex_key_cache](#complex-key-cache)
- [ssd_complex_key_cache](#ssd-cache)
- [complex_key_direct](#complex-key-direct)
- [ip_trie](#ip-trie)
### flat {#flat}
@ -107,7 +107,7 @@ or
LAYOUT(HASHED())
```
### sparse\_hashed {#dicts-external_dicts_dict_layout-sparse_hashed}
### sparse_hashed {#dicts-external_dicts_dict_layout-sparse_hashed}
Similar to `hashed`, but uses less memory in favor more CPU usage.
@ -123,7 +123,7 @@ Configuration example:
LAYOUT(SPARSE_HASHED())
```
### complex\_key\_hashed {#complex-key-hashed}
### complex_key_hashed {#complex-key-hashed}
This type of storage is for use with composite [keys](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md). Similar to `hashed`.
@ -139,7 +139,7 @@ Configuration example:
LAYOUT(COMPLEX_KEY_HASHED())
```
### range\_hashed {#range-hashed}
### range_hashed {#range-hashed}
The dictionary is stored in memory in the form of a hash table with an ordered array of ranges and their corresponding values.
@ -294,11 +294,11 @@ Set a large enough cache size. You need to experiment to select the number of ce
!!! warning "Warning"
Do not use ClickHouse as a source, because it is slow to process queries with random reads.
### complex\_key\_cache {#complex-key-cache}
### complex_key_cache {#complex-key-cache}
This type of storage is for use with composite [keys](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md). Similar to `cache`.
### ssd\_cache {#ssd-cache}
### ssd_cache {#ssd-cache}
Similar to `cache`, but stores data on SSD and index in RAM.
@ -328,9 +328,9 @@ LAYOUT(CACHE(BLOCK_SIZE 4096 FILE_SIZE 16777216 READ_BUFFER_SIZE 1048576
PATH /var/lib/clickhouse/clickhouse_dictionaries/test_dict MAX_STORED_KEYS 1048576))
```
### complex\_key\_ssd\_cache {#complex-key-ssd-cache}
### complex_key_ssd_cache {#complex-key-ssd-cache}
This type of storage is for use with composite [keys](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md). Similar to `ssd\_cache`.
This type of storage is for use with composite [keys](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md). Similar to `ssd_cache`.
### direct {#direct}
@ -354,11 +354,11 @@ or
LAYOUT(DIRECT())
```
### complex\_key\_direct {#complex-key-direct}
### complex_key_direct {#complex-key-direct}
This type of storage is for use with composite [keys](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-structure.md). Similar to `direct`.
### ip\_trie {#ip-trie}
### ip_trie {#ip-trie}
This type of storage is for mapping network prefixes (IP addresses) to metadata such as ASN.

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@ -13,9 +13,9 @@ ClickHouse:
- Periodically updates dictionaries and dynamically loads missing values. In other words, dictionaries can be loaded dynamically.
- Allows to create external dictionaries with xml files or [DDL queries](../../../sql-reference/statements/create/dictionary.md).
The configuration of external dictionaries can be located in one or more xml-files. The path to the configuration is specified in the [dictionaries\_config](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_config) parameter.
The configuration of external dictionaries can be located in one or more xml-files. The path to the configuration is specified in the [dictionaries_config](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_config) parameter.
Dictionaries can be loaded at server startup or at first use, depending on the [dictionaries\_lazy\_load](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_lazy_load) setting.
Dictionaries can be loaded at server startup or at first use, depending on the [dictionaries_lazy_load](../../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_lazy_load) setting.
The [dictionaries](../../../operations/system-tables/dictionaries.md#system_tables-dictionaries) system table contains information about dictionaries configured at server. For each dictionary you can find there:

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@ -1099,7 +1099,7 @@ Result:
## arrayAUC {#arrayauc}
Calculate AUC (Area Under the Curve, which is a concept in machine learning, see more details: https://en.wikipedia.org/wiki/Receiver\_operating\_characteristic\#Area\_under\_the\_curve).
Calculate AUC (Area Under the Curve, which is a concept in machine learning, see more details: https://en.wikipedia.org/wiki/Receiver_operating_characteristic#Area_under_the_curve).
**Syntax**

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@ -63,7 +63,7 @@ SELECT bitmapToArray(bitmapBuild([1, 2, 3, 4, 5])) AS res
## bitmapSubsetInRange {#bitmap-functions-bitmapsubsetinrange}
Return subset in specified range (not include the range\_end).
Return subset in specified range (not include the range_end).
``` sql
bitmapSubsetInRange(bitmap, range_start, range_end)
@ -239,7 +239,7 @@ SELECT bitmapCardinality(bitmapBuild([1, 2, 3, 4, 5])) AS res
## bitmapMin {#bitmapmin}
Retrun the smallest value of type UInt64 in the set, UINT32\_MAX if the set is empty.
Retrun the smallest value of type UInt64 in the set, UINT32_MAX if the set is empty.
bitmapMin(bitmap)
@ -286,8 +286,8 @@ Transform an array of values in a bitmap to another array of values, the result
**Parameters**
- `bitmap` – bitmap object.
- `from_array` – UInt32 array. For idx in range \[0, from\_array.size()), if bitmap contains from\_array\[idx\], then replace it with to\_array\[idx\]. Note that the result depends on array ordering if there are common elements between from\_array and to\_array.
- `to_array` – UInt32 array, its size shall be the same to from\_array.
- `from_array` – UInt32 array. For idx in range \[0, from_array.size()), if bitmap contains from_array\[idx\], then replace it with to_array\[idx\]. Note that the result depends on array ordering if there are common elements between from_array and to_array.
- `to_array` – UInt32 array, its size shall be the same to from_array.
**Example**

40
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@ -218,7 +218,7 @@ Rounds down a date with time to the start of the ten-minute interval.
Rounds down the date with time to the start of the fifteen-minute interval.
## toStartOfInterval(time\_or\_data, INTERVAL x unit \[, time\_zone\]) {#tostartofintervaltime-or-data-interval-x-unit-time-zone}
## toStartOfInterval(time_or_data, INTERVAL x unit \[, time_zone\]) {#tostartofintervaltime-or-data-interval-x-unit-time-zone}
This is a generalization of other functions named `toStartOf*`. For example,
`toStartOfInterval(t, INTERVAL 1 year)` returns the same as `toStartOfYear(t)`,
@ -339,7 +339,7 @@ SELECT toDate('2016-12-27') AS date, toYearWeek(date) AS yearWeek0, toYearWeek(d
└────────────┴───────────┴───────────┴───────────┘
```
## date_trunc(datepart, time\_or\_data\[, time\_zone\]), dateTrunc(datepart, time\_or\_data\[, time\_zone\]) {#date_trunc}
## date_trunc(datepart, time_or_data\[, time_zone\]), dateTrunc(datepart, time_or_data\[, time_zone\]) {#date_trunc}
Truncates a date or date with time based on the specified datepart, such as
- `second`
@ -486,20 +486,32 @@ For a time interval starting at ‘StartTime’ and continuing for ‘Duration
For example, `timeSlots(toDateTime('2012-01-01 12:20:00'), 600) = [toDateTime('2012-01-01 12:00:00'), toDateTime('2012-01-01 12:30:00')]`.
This is necessary for searching for pageviews in the corresponding session.
## formatDateTime(Time, Format\[, Timezone\]) {#formatdatetime}
## formatDateTime {#formatdatetime}
Function formats a Time according given Format string. N.B.: Format is a constant expression, e.g. you can not have multiple formats for single result column.
Supported modifiers for Format:
(“Example” column shows formatting result for time `2018-01-02 22:33:44`)
**Syntax**
| Modifier | Description | Example |
``` sql
formatDateTime(Time, Format\[, Timezone\])
```
**Returned value(s)**
Returnes time and date values according to the determined format.
**Replacement fields**
Using replacement fields, you can define a pattern for the resulting string. “Example” column shows formatting result for `2018-01-02 22:33:44`.
| Placeholder | Description | Example |
|----------|---------------------------------------------------------|------------|
| %C | year divided by 100 and truncated to integer (00-99) | 20 |
| %d | day of the month, zero-padded (01-31) | 02 |
| %D | Short MM/DD/YY date, equivalent to %m/%d/%y | 01/02/18 |
| %e | day of the month, space-padded ( 1-31) | 2 |
| %F | short YYYY-MM-DD date, equivalent to %Y-%m-%d | 2018-01-02 |
| %G | four-digit year format for ISO week number, calculated from the week-based year [defined by the ISO 8601](https://en.wikipedia.org/wiki/ISO_8601#Week_dates) standard, normally useful only with %V | 2018 |
| %g | two-digit year format, aligned to ISO 8601, abbreviated from four-digit notation | 18 |
| %H | hour in 24h format (00-23) | 22 |
| %I | hour in 12h format (01-12) | 10 |
| %j | day of the year (001-366) | 002 |
@ -518,6 +530,22 @@ Supported modifiers for Format:
| %Y | Year | 2018 |
| %% | a % sign | % |
**Example**
Query:
``` sql
SELECT formatDateTime(toDate('2010-01-04'), '%g')
```
Result:
```
┌─formatDateTime(toDate('2010-01-04'), '%g')─┐
│ 10 │
└────────────────────────────────────────────┘
```
[Original article](https://clickhouse.tech/docs/en/query_language/functions/date_time_functions/) <!--hide-->
## FROM_UNIXTIME

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@ -315,7 +315,7 @@ Calculates JumpConsistentHash form a UInt64.
Accepts two arguments: a UInt64-type key and the number of buckets. Returns Int32.
For more information, see the link: [JumpConsistentHash](https://arxiv.org/pdf/1406.2294.pdf)
## murmurHash2\_32, murmurHash2\_64 {#murmurhash2-32-murmurhash2-64}
## murmurHash2_32, murmurHash2_64 {#murmurhash2-32-murmurhash2-64}
Produces a [MurmurHash2](https://github.com/aappleby/smhasher) hash value.
@ -383,7 +383,7 @@ Result:
└──────────────────────┴─────────────────────┘
```
## murmurHash3\_32, murmurHash3\_64 {#murmurhash3-32-murmurhash3-64}
## murmurHash3_32, murmurHash3_64 {#murmurhash3-32-murmurhash3-64}
Produces a [MurmurHash3](https://github.com/aappleby/smhasher) hash value.
@ -413,7 +413,7 @@ SELECT murmurHash3_32(array('e','x','a'), 'mple', 10, toDateTime('2019-06-15 23:
└─────────────┴────────┘
```
## murmurHash3\_128 {#murmurhash3-128}
## murmurHash3_128 {#murmurhash3-128}
Produces a 128-bit [MurmurHash3](https://github.com/aappleby/smhasher) hash value.

4
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@ -14,11 +14,11 @@ For proper operation of introspection functions:
- Install the `clickhouse-common-static-dbg` package.
- Set the [allow\_introspection\_functions](../../operations/settings/settings.md#settings-allow_introspection_functions) setting to 1.
- Set the [allow_introspection_functions](../../operations/settings/settings.md#settings-allow_introspection_functions) setting to 1.
For security reasons introspection functions are disabled by default.
ClickHouse saves profiler reports to the [trace\_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) system table. Make sure the table and profiler are configured properly.
ClickHouse saves profiler reports to the [trace_log](../../operations/system-tables/trace_log.md#system_tables-trace_log) system table. Make sure the table and profiler are configured properly.
## addressToLine {#addresstoline}

24
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@ -73,7 +73,7 @@ SELECT isValidJSON('{"a": "hello", "b": [-100, 200.0, 300]}') = 1
SELECT isValidJSON('not a json') = 0
```
## JSONHas(json\[, indices\_or\_keys\]…) {#jsonhasjson-indices-or-keys}
## JSONHas(json\[, indices_or_keys\]…) {#jsonhasjson-indices-or-keys}
If the value exists in the JSON document, `1` will be returned.
@ -106,7 +106,7 @@ SELECT JSONExtractKey('{"a": "hello", "b": [-100, 200.0, 300]}', -2) = 'a'
SELECT JSONExtractString('{"a": "hello", "b": [-100, 200.0, 300]}', 1) = 'hello'
```
## JSONLength(json\[, indices\_or\_keys\]…) {#jsonlengthjson-indices-or-keys}
## JSONLength(json\[, indices_or_keys\]…) {#jsonlengthjson-indices-or-keys}
Return the length of a JSON array or a JSON object.
@ -119,7 +119,7 @@ SELECT JSONLength('{"a": "hello", "b": [-100, 200.0, 300]}', 'b') = 3
SELECT JSONLength('{"a": "hello", "b": [-100, 200.0, 300]}') = 2
```
## JSONType(json\[, indices\_or\_keys\]…) {#jsontypejson-indices-or-keys}
## JSONType(json\[, indices_or_keys\]…) {#jsontypejson-indices-or-keys}
Return the type of a JSON value.
@ -133,13 +133,13 @@ SELECT JSONType('{"a": "hello", "b": [-100, 200.0, 300]}', 'a') = 'String'
SELECT JSONType('{"a": "hello", "b": [-100, 200.0, 300]}', 'b') = 'Array'
```
## JSONExtractUInt(json\[, indices\_or\_keys\]…) {#jsonextractuintjson-indices-or-keys}
## JSONExtractUInt(json\[, indices_or_keys\]…) {#jsonextractuintjson-indices-or-keys}
## JSONExtractInt(json\[, indices\_or\_keys\]…) {#jsonextractintjson-indices-or-keys}
## JSONExtractInt(json\[, indices_or_keys\]…) {#jsonextractintjson-indices-or-keys}
## JSONExtractFloat(json\[, indices\_or\_keys\]…) {#jsonextractfloatjson-indices-or-keys}
## JSONExtractFloat(json\[, indices_or_keys\]…) {#jsonextractfloatjson-indices-or-keys}
## JSONExtractBool(json\[, indices\_or\_keys\]…) {#jsonextractbooljson-indices-or-keys}
## JSONExtractBool(json\[, indices_or_keys\]…) {#jsonextractbooljson-indices-or-keys}
Parses a JSON and extract a value. These functions are similar to `visitParam` functions.
@ -153,7 +153,7 @@ SELECT JSONExtractFloat('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', 2) = 200
SELECT JSONExtractUInt('{"a": "hello", "b": [-100, 200.0, 300]}', 'b', -1) = 300
```
## JSONExtractString(json\[, indices\_or\_keys\]…) {#jsonextractstringjson-indices-or-keys}
## JSONExtractString(json\[, indices_or_keys\]…) {#jsonextractstringjson-indices-or-keys}
Parses a JSON and extract a string. This function is similar to `visitParamExtractString` functions.
@ -171,7 +171,7 @@ SELECT JSONExtractString('{"abc":"\\u263"}', 'abc') = ''
SELECT JSONExtractString('{"abc":"hello}', 'abc') = ''
```
## JSONExtract(json\[, indices\_or\_keys…\], Return\_type) {#jsonextractjson-indices-or-keys-return-type}
## JSONExtract(json\[, indices_or_keys…\], Return_type) {#jsonextractjson-indices-or-keys-return-type}
Parses a JSON and extract a value of the given ClickHouse data type.
@ -192,7 +192,7 @@ SELECT JSONExtract('{"day": "Thursday"}', 'day', 'Enum8(\'Sunday\' = 0, \'Monday
SELECT JSONExtract('{"day": 5}', 'day', 'Enum8(\'Sunday\' = 0, \'Monday\' = 1, \'Tuesday\' = 2, \'Wednesday\' = 3, \'Thursday\' = 4, \'Friday\' = 5, \'Saturday\' = 6)') = 'Friday'
```
## JSONExtractKeysAndValues(json\[, indices\_or\_keys…\], Value\_type) {#jsonextractkeysandvaluesjson-indices-or-keys-value-type}
## JSONExtractKeysAndValues(json\[, indices_or_keys…\], Value_type) {#jsonextractkeysandvaluesjson-indices-or-keys-value-type}
Parses key-value pairs from a JSON where the values are of the given ClickHouse data type.
@ -202,7 +202,7 @@ Example:
SELECT JSONExtractKeysAndValues('{"x": {"a": 5, "b": 7, "c": 11}}', 'x', 'Int8') = [('a',5),('b',7),('c',11)]
```
## JSONExtractRaw(json\[, indices\_or\_keys\]…) {#jsonextractrawjson-indices-or-keys}
## JSONExtractRaw(json\[, indices_or_keys\]…) {#jsonextractrawjson-indices-or-keys}
Returns a part of JSON as unparsed string.
@ -214,7 +214,7 @@ Example:
SELECT JSONExtractRaw('{"a": "hello", "b": [-100, 200.0, 300]}', 'b') = '[-100, 200.0, 300]'
```
## JSONExtractArrayRaw(json\[, indices\_or\_keys…\]) {#jsonextractarrayrawjson-indices-or-keys}
## JSONExtractArrayRaw(json\[, indices_or_keys…\]) {#jsonextractarrayrawjson-indices-or-keys}
Returns an array with elements of JSON array, each represented as unparsed string.

16
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@ -417,7 +417,7 @@ ORDER BY h ASC
Transforms a value according to the explicitly defined mapping of some elements to other ones.
There are two variations of this function:
### transform(x, array\_from, array\_to, default) {#transformx-array-from-array-to-default}
### transform(x, array_from, array_to, default) {#transformx-array-from-array-to-default}
`x` – What to transform.
@ -437,7 +437,7 @@ Types:
Where the same letter is indicated (T or U), for numeric types these might not be matching types, but types that have a common type.
For example, the first argument can have the Int64 type, while the second has the Array(UInt16) type.
If the ‘x’ value is equal to one of the elements in the ‘array\_from’ array, it returns the existing element (that is numbered the same) from the ‘array\_to’ array. Otherwise, it returns ‘default’. If there are multiple matching elements in ‘array\_from’, it returns one of the matches.
If the ‘x’ value is equal to one of the elements in the ‘array_from’ array, it returns the existing element (that is numbered the same) from the ‘array_to’ array. Otherwise, it returns ‘default’. If there are multiple matching elements in ‘array_from’, it returns one of the matches.
Example:
@ -459,10 +459,10 @@ ORDER BY c DESC
└───────────┴────────┘
```
### transform(x, array\_from, array\_to) {#transformx-array-from-array-to}
### transform(x, array_from, array_to) {#transformx-array-from-array-to}
Differs from the first variation in that the ‘default’ argument is omitted.
If the ‘x’ value is equal to one of the elements in the ‘array\_from’ array, it returns the matching element (that is numbered the same) from the ‘array\_to’ array. Otherwise, it returns ‘x’.
If the ‘x’ value is equal to one of the elements in the ‘array_from’ array, it returns the matching element (that is numbered the same) from the ‘array_to’ array. Otherwise, it returns ‘x’.
Types:
@ -1293,7 +1293,7 @@ joinGet(join_storage_table_name, `value_column`, join_keys)
Returns list of values corresponded to list of keys.
If certain doesn’t exist in source table then `0` or `null` will be returned based on [join\_use\_nulls](../../operations/settings/settings.md#join_use_nulls) setting.
If certain doesn’t exist in source table then `0` or `null` will be returned based on [join_use_nulls](../../operations/settings/settings.md#join_use_nulls) setting.
More info about `join_use_nulls` in [Join operation](../../engines/table-engines/special/join.md).
@ -1332,15 +1332,15 @@ Result:
└──────────────────────────────────────────────────┘
```
## modelEvaluate(model\_name, …) {#function-modelevaluate}
## modelEvaluate(model_name, …) {#function-modelevaluate}
Evaluate external model.
Accepts a model name and model arguments. Returns Float64.
## throwIf(x\[, custom\_message\]) {#throwifx-custom-message}
## throwIf(x\[, custom_message\]) {#throwifx-custom-message}
Throw an exception if the argument is non zero.
custom\_message - is an optional parameter: a constant string, provides an error message
custom_message - is an optional parameter: a constant string, provides an error message
``` sql
SELECT throwIf(number = 3, 'Too many') FROM numbers(10);

6
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@ -32,12 +32,12 @@ The function also works for arrays.
Returns the length of a string in Unicode code points (not in characters), assuming that the string contains a set of bytes that make up UTF-8 encoded text. If this assumption is not met, it returns some result (it doesn’t throw an exception).
The result type is UInt64.
## char\_length, CHAR\_LENGTH {#char-length}
## char_length, CHAR_LENGTH {#char-length}
Returns the length of a string in Unicode code points (not in characters), assuming that the string contains a set of bytes that make up UTF-8 encoded text. If this assumption is not met, it returns some result (it doesn’t throw an exception).
The result type is UInt64.
## character\_length, CHARACTER\_LENGTH {#character-length}
## character_length, CHARACTER_LENGTH {#character-length}
Returns the length of a string in Unicode code points (not in characters), assuming that the string contains a set of bytes that make up UTF-8 encoded text. If this assumption is not met, it returns some result (it doesn’t throw an exception).
The result type is UInt64.
@ -78,7 +78,7 @@ toValidUTF8( input_string )
Parameters:
- input\_string — Any set of bytes represented as the [String](../../sql-reference/data-types/string.md) data type object.
- input_string — Any set of bytes represented as the [String](../../sql-reference/data-types/string.md) data type object.
Returned value: Valid UTF-8 string.

2
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@ -250,7 +250,7 @@ YYYY-MM-DD
YYYY-MM-DD hh:mm:ss
```
As an exception, if converting from UInt32, Int32, UInt64, or Int64 numeric types to Date, and if the number is greater than or equal to 65536, the number is interpreted as a Unix timestamp (and not as the number of days) and is rounded to the date. This allows support for the common occurrence of writing ‘toDate(unix\_timestamp)’, which otherwise would be an error and would require writing the more cumbersome ‘toDate(toDateTime(unix\_timestamp))’.
As an exception, if converting from UInt32, Int32, UInt64, or Int64 numeric types to Date, and if the number is greater than or equal to 65536, the number is interpreted as a Unix timestamp (and not as the number of days) and is rounded to the date. This allows support for the common occurrence of writing ‘toDate(unix_timestamp)’, which otherwise would be an error and would require writing the more cumbersome ‘toDate(toDateTime(unix_timestamp))’.
Conversion between a date and date with time is performed the natural way: by adding a null time or dropping the time.

8
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@ -117,7 +117,7 @@ Returns the part of the domain that includes top-level subdomains up to the “f
For example, `cutToFirstSignificantSubdomain('https://news.yandex.com.tr/') = 'yandex.com.tr'`.
### port(URL\[, default\_port = 0\]) {#port}
### port(URL\[, default_port = 0\]) {#port}
Returns the port or `default_port` if there is no port in the URL (or in case of validation error).
@ -127,11 +127,11 @@ Returns the path. Example: `/top/news.html` The path does not include the query
### pathFull {#pathfull}
The same as above, but including query string and fragment. Example: /top/news.html?page=2\#comments
The same as above, but including query string and fragment. Example: /top/news.html?page=2#comments
### queryString {#querystring}
Returns the query string. Example: page=1&lr=213. query-string does not include the initial question mark, as well as \# and everything after \#.
Returns the query string. Example: page=1&lr=213. query-string does not include the initial question mark, as well as # and everything after #.
### fragment {#fragment}
@ -139,7 +139,7 @@ Returns the fragment identifier. fragment does not include the initial hash symb
### queryStringAndFragment {#querystringandfragment}
Returns the query string and fragment identifier. Example: page=1\#29390.
Returns the query string and fragment identifier. Example: page=1#29390.
### extractURLParameter(URL, name) {#extracturlparameterurl-name}

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@ -15,12 +15,12 @@ ClickHouse supports working with multiple alternative geobases (regional hierarc
The ‘clickhouse-server’ config specifies the file with the regional hierarchy::`<path_to_regions_hierarchy_file>/opt/geo/regions_hierarchy.txt</path_to_regions_hierarchy_file>`
Besides this file, it also searches for files nearby that have the \_ symbol and any suffix appended to the name (before the file extension).
Besides this file, it also searches for files nearby that have the _ symbol and any suffix appended to the name (before the file extension).
For example, it will also find the file `/opt/geo/regions_hierarchy_ua.txt`, if present.
`ua` is called the dictionary key. For a dictionary without a suffix, the key is an empty string.
All the dictionaries are re-loaded in runtime (once every certain number of seconds, as defined in the builtin\_dictionaries\_reload\_interval config parameter, or once an hour by default). However, the list of available dictionaries is defined one time, when the server starts.
All the dictionaries are re-loaded in runtime (once every certain number of seconds, as defined in the builtin_dictionaries_reload_interval config parameter, or once an hour by default). However, the list of available dictionaries is defined one time, when the server starts.
All functions for working with regions have an optional argument at the end – the dictionary key. It is referred to as the geobase.
Example:
@ -105,7 +105,7 @@ Example: `regionToCountry(toUInt32(213)) = 225` converts Moscow (213) to Russia
Converts a region to a continent. In every other way, this function is the same as ‘regionToCity’.
Example: `regionToContinent(toUInt32(213)) = 10001` converts Moscow (213) to Eurasia (10001).
### regionToTopContinent (\#regiontotopcontinent) {#regiontotopcontinent-regiontotopcontinent}
### regionToTopContinent (#regiontotopcontinent) {#regiontotopcontinent-regiontotopcontinent}
Finds the highest continent in the hierarchy for the region.

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@ -64,7 +64,7 @@ A subquery in the IN clause is always run just one time on a single server. Ther
## NULL Processing {#in-null-processing}
During request processing, the `IN` operator assumes that the result of an operation with [NULL](../../sql-reference/syntax.md#null-literal) always equals `0`, regardless of whether `NULL` is on the right or left side of the operator. `NULL` values are not included in any dataset, do not correspond to each other and cannot be compared if [transform\_null\_in = 0](../../operations/settings/settings.md#transform_null_in).
During request processing, the `IN` operator assumes that the result of an operation with [NULL](../../sql-reference/syntax.md#null-literal) always equals `0`, regardless of whether `NULL` is on the right or left side of the operator. `NULL` values are not included in any dataset, do not correspond to each other and cannot be compared if [transform_null_in = 0](../../operations/settings/settings.md#transform_null_in).
Here is an example with the `t_null` table:
@ -112,9 +112,9 @@ For a non-distributed query, use the regular `IN` / `JOIN`.
Be careful when using subqueries in the `IN` / `JOIN` clauses for distributed query processing.
Let’s look at some examples. Assume that each server in the cluster has a normal **local\_table**. Each server also has a **distributed\_table** table with the **Distributed** type, which looks at all the servers in the cluster.
Let’s look at some examples. Assume that each server in the cluster has a normal **local_table**. Each server also has a **distributed_table** table with the **Distributed** type, which looks at all the servers in the cluster.
For a query to the **distributed\_table**, the query will be sent to all the remote servers and run on them using the **local\_table**.
For a query to the **distributed_table**, the query will be sent to all the remote servers and run on them using the **local_table**.
For example, the query
@ -148,7 +148,7 @@ In other words, the data set in the IN clause will be collected on each server i
This will work correctly and optimally if you are prepared for this case and have spread data across the cluster servers such that the data for a single UserID resides entirely on a single server. In this case, all the necessary data will be available locally on each server. Otherwise, the result will be inaccurate. We refer to this variation of the query as “local IN”.
To correct how the query works when data is spread randomly across the cluster servers, you could specify **distributed\_table** inside a subquery. The query would look like this:
To correct how the query works when data is spread randomly across the cluster servers, you could specify **distributed_table** inside a subquery. The query would look like this:
``` sql
SELECT uniq(UserID) FROM distributed_table WHERE CounterID = 101500 AND UserID IN (SELECT UserID FROM distributed_table WHERE CounterID = 34)

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@ -240,7 +240,7 @@ You can specify the partition expression in `ALTER ... PARTITION` queries in dif
- As a value from the `partition` column of the `system.parts` table. For example, `ALTER TABLE visits DETACH PARTITION 201901`.
- As the expression from the table column. Constants and constant expressions are supported. For example, `ALTER TABLE visits DETACH PARTITION toYYYYMM(toDate('2019-01-25'))`.
- Using the partition ID. Partition ID is a string identifier of the partition (human-readable, if possible) that is used as the names of partitions in the file system and in ZooKeeper. The partition ID must be specified in the `PARTITION ID` clause, in a single quotes. For example, `ALTER TABLE visits DETACH PARTITION ID '201901'`.
- In the [ALTER ATTACH PART](#alter_attach-partition) and [DROP DETACHED PART](#alter_drop-detached) query, to specify the name of a part, use string literal with a value from the `name` column of the [system.detached\_parts](../../../operations/system-tables/detached_parts.md#system_tables-detached_parts) table. For example, `ALTER TABLE visits ATTACH PART '201901_1_1_0'`.
- In the [ALTER ATTACH PART](#alter_attach-partition) and [DROP DETACHED PART](#alter_drop-detached) query, to specify the name of a part, use string literal with a value from the `name` column of the [system.detached_parts](../../../operations/system-tables/detached_parts.md#system_tables-detached_parts) table. For example, `ALTER TABLE visits ATTACH PART '201901_1_1_0'`.
Usage of quotes when specifying the partition depends on the type of partition expression. For example, for the `String` type, you have to specify its name in quotes (`'`). For the `Date` and `Int*` types no quotes are needed.

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@ -37,6 +37,6 @@ For `MergeTree` family engines, the `CHECK TABLE` query shows a check status for
If the table is corrupted, you can copy the non-corrupted data to another table. To do this:
1. Create a new table with the same structure as damaged table. To do this execute the query `CREATE TABLE <new_table_name> AS <damaged_table_name>`.
2. Set the [max\_threads](../../operations/settings/settings.md#settings-max_threads) value to 1 to process the next query in a single thread. To do this run the query `SET max_threads = 1`.
2. Set the [max_threads](../../operations/settings/settings.md#settings-max_threads) value to 1 to process the next query in a single thread. To do this run the query `SET max_threads = 1`.
3. Execute the query `INSERT INTO <new_table_name> SELECT * FROM <damaged_table_name>`. This request copies the non-corrupted data from the damaged table to another table. Only the data before the corrupted part will be copied.
4. Restart the `clickhouse-client` to reset the `max_threads` value.

2
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@ -18,7 +18,7 @@ The query can specify a list of columns to insert `[(c1, c2, c3)]`. In this case
- The values calculated from the `DEFAULT` expressions specified in the table definition.
- Zeros and empty strings, if `DEFAULT` expressions are not defined.
If [strict\_insert\_defaults=1](../../operations/settings/settings.md), columns that do not have `DEFAULT` defined must be listed in the query.
If [strict_insert_defaults=1](../../operations/settings/settings.md), columns that do not have `DEFAULT` defined must be listed in the query.
Data can be passed to the INSERT in any [format](../../interfaces/formats.md#formats) supported by ClickHouse. The format must be specified explicitly in the query:

2
docs/en/sql-reference/statements/optimize.md
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@ -15,7 +15,7 @@ The `OPTMIZE` query is also supported for the [MaterializedView](../../engines/t
When `OPTIMIZE` is used with the [ReplicatedMergeTree](../../engines/table-engines/mergetree-family/replication.md) family of table engines, ClickHouse creates a task for merging and waits for execution on all nodes (if the `replication_alter_partitions_sync` setting is enabled).
- If `OPTIMIZE` doesn’t perform a merge for any reason, it doesn’t notify the client. To enable notifications, use the [optimize\_throw\_if\_noop](../../operations/settings/settings.md#setting-optimize_throw_if_noop) setting.
- If `OPTIMIZE` doesn’t perform a merge for any reason, it doesn’t notify the client. To enable notifications, use the [optimize_throw_if_noop](../../operations/settings/settings.md#setting-optimize_throw_if_noop) setting.
- If you specify a `PARTITION`, only the specified partition is optimized. [How to set partition expression](../../sql-reference/statements/alter/index.md#alter-how-to-specify-part-expr).
- If you specify `FINAL`, optimization is performed even when all the data is already in one part.
- If you specify `DEDUPLICATE`, then completely identical rows will be deduplicated (all columns are compared), it makes sense only for the MergeTree engine.

8
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@ -66,9 +66,9 @@ The other alternatives include only the rows that pass through HAVING in ‘tota
`after_having_exclusive` – Don’t include rows that didn’t pass through `max_rows_to_group_by`. In other words, ‘totals’ will have less than or the same number of rows as it would if `max_rows_to_group_by` were omitted.
`after_having_inclusive` – Include all the rows that didn’t pass through ‘max\_rows\_to\_group\_by’ in ‘totals’. In other words, ‘totals’ will have more than or the same number of rows as it would if `max_rows_to_group_by` were omitted.
`after_having_inclusive` – Include all the rows that didn’t pass through ‘max_rows_to_group_by’ in ‘totals’. In other words, ‘totals’ will have more than or the same number of rows as it would if `max_rows_to_group_by` were omitted.
`after_having_auto` – Count the number of rows that passed through HAVING. If it is more than a certain amount (by default, 50%), include all the rows that didn’t pass through ‘max\_rows\_to\_group\_by’ in ‘totals’. Otherwise, do not include them.
`after_having_auto` – Count the number of rows that passed through HAVING. If it is more than a certain amount (by default, 50%), include all the rows that didn’t pass through ‘max_rows_to_group_by’ in ‘totals’. Otherwise, do not include them.
`totals_auto_threshold` – By default, 0.5. The coefficient for `after_having_auto`.
@ -116,11 +116,11 @@ Aggregation is one of the most important features of a column-oriented DBMS, and
### GROUP BY in External Memory {#select-group-by-in-external-memory}
You can enable dumping temporary data to the disk to restrict memory usage during `GROUP BY`.
The [max\_bytes\_before\_external\_group\_by](../../../operations/settings/settings.md#settings-max_bytes_before_external_group_by) setting determines the threshold RAM consumption for dumping `GROUP BY` temporary data to the file system. If set to 0 (the default), it is disabled.
The [max_bytes_before_external_group_by](../../../operations/settings/settings.md#settings-max_bytes_before_external_group_by) setting determines the threshold RAM consumption for dumping `GROUP BY` temporary data to the file system. If set to 0 (the default), it is disabled.
When using `max_bytes_before_external_group_by`, we recommend that you set `max_memory_usage` about twice as high. This is necessary because there are two stages to aggregation: reading the data and forming intermediate data (1) and merging the intermediate data (2). Dumping data to the file system can only occur during stage 1. If the temporary data wasn’t dumped, then stage 2 might require up to the same amount of memory as in stage 1.
For example, if [max\_memory\_usage](../../../operations/settings/settings.md#settings_max_memory_usage) was set to 10000000000 and you want to use external aggregation, it makes sense to set `max_bytes_before_external_group_by` to 10000000000, and `max_memory_usage` to 20000000000. When external aggregation is triggered (if there was at least one dump of temporary data), maximum consumption of RAM is only slightly more than `max_bytes_before_external_group_by`.
For example, if [max_memory_usage](../../../operations/settings/settings.md#settings_max_memory_usage) was set to 10000000000 and you want to use external aggregation, it makes sense to set `max_bytes_before_external_group_by` to 10000000000, and `max_memory_usage` to 20000000000. When external aggregation is triggered (if there was at least one dump of temporary data), maximum consumption of RAM is only slightly more than `max_bytes_before_external_group_by`.
With distributed query processing, external aggregation is performed on remote servers. In order for the requester server to use only a small amount of RAM, set `distributed_aggregation_memory_efficient` to 1.

10
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@ -39,7 +39,7 @@ Additional join types available in ClickHouse:
## Setting {#join-settings}
!!! note "Note"
The default join type can be overriden using [join\_default\_strictness](../../../operations/settings/settings.md#settings-join_default_strictness) setting.
The default join type can be overriden using [join_default_strictness](../../../operations/settings/settings.md#settings-join_default_strictness) setting.
Also the behavior of ClickHouse server for `ANY JOIN` operations depends on the [any_join_distinct_right_table_keys](../../../operations/settings/settings.md#any_join_distinct_right_table_keys) setting.
@ -106,7 +106,7 @@ Be careful when using `GLOBAL`. For more information, see the [Distributed subqu
### Processing of Empty or NULL Cells {#processing-of-empty-or-null-cells}
While joining tables, the empty cells may appear. The setting [join\_use\_nulls](../../../operations/settings/settings.md#join_use_nulls) define how ClickHouse fills these cells.
While joining tables, the empty cells may appear. The setting [join_use_nulls](../../../operations/settings/settings.md#join_use_nulls) define how ClickHouse fills these cells.
If the `JOIN` keys are [Nullable](../../../sql-reference/data-types/nullable.md) fields, the rows where at least one of the keys has the value [NULL](../../../sql-reference/syntax.md#null-literal) are not joined.
@ -143,10 +143,10 @@ By default, ClickHouse uses the [hash join](https://en.wikipedia.org/wiki/Hash_j
If you need to restrict join operation memory consumption use the following settings:
- [max\_rows\_in\_join](../../../operations/settings/query-complexity.md#settings-max_rows_in_join) — Limits number of rows in the hash table.
- [max\_bytes\_in\_join](../../../operations/settings/query-complexity.md#settings-max_bytes_in_join) — Limits size of the hash table.
- [max_rows_in_join](../../../operations/settings/query-complexity.md#settings-max_rows_in_join) — Limits number of rows in the hash table.
- [max_bytes_in_join](../../../operations/settings/query-complexity.md#settings-max_bytes_in_join) — Limits size of the hash table.
When any of these limits is reached, ClickHouse acts as the [join\_overflow\_mode](../../../operations/settings/query-complexity.md#settings-join_overflow_mode) setting instructs.
When any of these limits is reached, ClickHouse acts as the [join_overflow_mode](../../../operations/settings/query-complexity.md#settings-join_overflow_mode) setting instructs.
## Examples {#examples}

10
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@ -47,12 +47,12 @@ Always returns `Ok.` regardless of the result of the internal dictionary update.
## RELOAD DICTIONARIES {#query_language-system-reload-dictionaries}
Reloads all dictionaries that have been successfully loaded before.
By default, dictionaries are loaded lazily (see [dictionaries\_lazy\_load](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_lazy_load)), so instead of being loaded automatically at startup, they are initialized on first access through dictGet function or SELECT from tables with ENGINE = Dictionary. The `SYSTEM RELOAD DICTIONARIES` query reloads such dictionaries (LOADED).
By default, dictionaries are loaded lazily (see [dictionaries_lazy_load](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-dictionaries_lazy_load)), so instead of being loaded automatically at startup, they are initialized on first access through dictGet function or SELECT from tables with ENGINE = Dictionary. The `SYSTEM RELOAD DICTIONARIES` query reloads such dictionaries (LOADED).
Always returns `Ok.` regardless of the result of the dictionary update.
## RELOAD DICTIONARY {#query_language-system-reload-dictionary}
Completely reloads a dictionary `dictionary_name`, regardless of the state of the dictionary (LOADED / NOT\_LOADED / FAILED).
Completely reloads a dictionary `dictionary_name`, regardless of the state of the dictionary (LOADED / NOT_LOADED / FAILED).
Always returns `Ok.` regardless of the result of updating the dictionary.
The status of the dictionary can be checked by querying the `system.dictionaries` table.
@ -64,7 +64,7 @@ SELECT name, status FROM system.dictionaries;
Resets ClickHouse’s internal DNS cache. Sometimes (for old ClickHouse versions) it is necessary to use this command when changing the infrastructure (changing the IP address of another ClickHouse server or the server used by dictionaries).
For more convenient (automatic) cache management, see disable\_internal\_dns\_cache, dns\_cache\_update\_period parameters.
For more convenient (automatic) cache management, see disable_internal_dns_cache, dns_cache_update_period parameters.
## DROP MARK CACHE {#query_language-system-drop-mark-cache}
@ -91,7 +91,7 @@ The fourth one is useful to remove metadata of dead replica when all other repli
## DROP UNCOMPRESSED CACHE {#query_language-system-drop-uncompressed-cache}
Reset the uncompressed data cache. Used in development of ClickHouse and performance tests.
For manage uncompressed data cache parameters use following server level settings [uncompressed\_cache\_size](../../operations/server-configuration-parameters/settings.md#server-settings-uncompressed_cache_size) and query/user/profile level settings [use\_uncompressed\_cache](../../operations/settings/settings.md#setting-use_uncompressed_cache)
For manage uncompressed data cache parameters use following server level settings [uncompressed_cache_size](../../operations/server-configuration-parameters/settings.md#server-settings-uncompressed_cache_size) and query/user/profile level settings [use_uncompressed_cache](../../operations/settings/settings.md#setting-use_uncompressed_cache)
## DROP COMPILED EXPRESSION CACHE {#query_language-system-drop-compiled-expression-cache}
@ -100,7 +100,7 @@ Complied expression cache used when query/user/profile enable option [compile](.
## FLUSH LOGS {#query_language-system-flush_logs}
Flushes buffers of log messages to system tables (e.g. system.query\_log). Allows you to not wait 7.5 seconds when debugging.
Flushes buffers of log messages to system tables (e.g. system.query_log). Allows you to not wait 7.5 seconds when debugging.
This will also create system tables even if message queue is empty.
## RELOAD CONFIG {#query_language-system-reload-config}

6
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@ -13,9 +13,9 @@ The `INSERT` query uses both parsers:
INSERT INTO t VALUES (1, 'Hello, world'), (2, 'abc'), (3, 'def')
```
The `INSERT INTO t VALUES` fragment is parsed by the full parser, and the data `(1, 'Hello, world'), (2, 'abc'), (3, 'def')` is parsed by the fast stream parser. You can also turn on the full parser for the data by using the [input\_format\_values\_interpret\_expressions](../operations/settings/settings.md#settings-input_format_values_interpret_expressions) setting. When `input_format_values_interpret_expressions = 1`, ClickHouse first tries to parse values with the fast stream parser. If it fails, ClickHouse tries to use the full parser for the data, treating it like an SQL [expression](#syntax-expressions).
The `INSERT INTO t VALUES` fragment is parsed by the full parser, and the data `(1, 'Hello, world'), (2, 'abc'), (3, 'def')` is parsed by the fast stream parser. You can also turn on the full parser for the data by using the [input_format_values_interpret_expressions](../operations/settings/settings.md#settings-input_format_values_interpret_expressions) setting. When `input_format_values_interpret_expressions = 1`, ClickHouse first tries to parse values with the fast stream parser. If it fails, ClickHouse tries to use the full parser for the data, treating it like an SQL [expression](#syntax-expressions).
Data can have any format. When a query is received, the server calculates no more than [max\_query\_size](../operations/settings/settings.md#settings-max_query_size) bytes of the request in RAM (by default, 1 MB), and the rest is stream parsed.
Data can have any format. When a query is received, the server calculates no more than [max_query_size](../operations/settings/settings.md#settings-max_query_size) bytes of the request in RAM (by default, 1 MB), and the rest is stream parsed.
It allows for avoiding issues with large `INSERT` queries.
When using the `Values` format in an `INSERT` query, it may seem that data is parsed the same as expressions in a `SELECT` query, but this is not true. The `Values` format is much more limited.
@ -40,7 +40,7 @@ Keywords are case-insensitive when they correspond to:
- SQL standard. For example, `SELECT`, `select` and `SeLeCt` are all valid.
- Implementation in some popular DBMS (MySQL or Postgres). For example, `DateTime` is the same as `datetime`.
You can check whether a data type name is case-sensitive in the [system.data\_type\_families](../operations/system-tables/data_type_families.md#system_tables-data_type_families) table.
You can check whether a data type name is case-sensitive in the [system.data_type_families](../operations/system-tables/data_type_families.md#system_tables-data_type_families) table.
In contrast to standard SQL, all other keywords (including functions names) are **case-sensitive**.

4
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@ -34,5 +34,5 @@ Connection settings like `host`, `port`, `user`, `password`, `compression`, `sec
**See Also**
- [skip\_unavailable\_shards](../../operations/settings/settings.md#settings-skip_unavailable_shards)
- [load\_balancing](../../operations/settings/settings.md#settings-load_balancing)
- [skip_unavailable_shards](../../operations/settings/settings.md#settings-skip_unavailable_shards)
- [load_balancing](../../operations/settings/settings.md#settings-load_balancing)

14
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@ -13,7 +13,7 @@ file(path, format, structure)
**Input parameters**
- `path` — The relative path to the file from [user\_files\_path](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-user_files_path). Path to file support following globs in readonly mode: `*`, `?`, `{abc,def}` and `{N..M}` where `N`, `M` — numbers, \``'abc', 'def'` — strings.
- `path` — The relative path to the file from [user_files_path](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-user_files_path). Path to file support following globs in readonly mode: `*`, `?`, `{abc,def}` and `{N..M}` where `N`, `M` — numbers, \``'abc', 'def'` — strings.
- `format` — The [format](../../interfaces/formats.md#formats) of the file.
- `structure` — Structure of the table. Format `'column1_name column1_type, column2_name column2_type, ...'`.
@ -70,12 +70,12 @@ Constructions with `{}` are similar to the [remote table function](../../sql-ref
1. Suppose we have several files with the following relative paths:
- ‘some\_dir/some\_file\_1’
- ‘some\_dir/some\_file\_2’
- ‘some\_dir/some\_file\_3’
- ‘another\_dir/some\_file\_1’
- ‘another\_dir/some\_file\_2’
- ‘another\_dir/some\_file\_3’
- ‘some_dir/some_file_1’
- ‘some_dir/some_file_2’
- ‘some_dir/some_file_3’
- ‘another_dir/some_file_1’
- ‘another_dir/some_file_2’
- ‘another_dir/some_file_3’
1. Query the amount of rows in these files:

12
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@ -53,12 +53,12 @@ Constructions with `{}` are similar to the [remote table function](../../sql-ref
1. Suppose that we have several files with following URIs on HDFS:
- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_1’
- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_2’
- ‘hdfs://hdfs1:9000/some\_dir/some\_file\_3’
- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_1’
- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_2’
- ‘hdfs://hdfs1:9000/another\_dir/some\_file\_3’
- ‘hdfs://hdfs1:9000/some_dir/some_file_1’
- ‘hdfs://hdfs1:9000/some_dir/some_file_2’
- ‘hdfs://hdfs1:9000/some_dir/some_file_3’
- ‘hdfs://hdfs1:9000/another_dir/some_file_1’
- ‘hdfs://hdfs1:9000/another_dir/some_file_2’
- ‘hdfs://hdfs1:9000/another_dir/some_file_3’
2. Query the amount of rows in these files:

4
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@ -14,12 +14,12 @@ You can use table functions in:
The method for creating a temporary table that is available only in the current query. The table is deleted when the query finishes.
- [CREATE TABLE AS \<table\_function()\>](../../sql-reference/statements/create/table.md) query.
- [CREATE TABLE AS \<table_function()\>](../../sql-reference/statements/create/table.md) query.
It's one of the methods of creating a table.
!!! warning "Warning"
You can’t use table functions if the [allow\_ddl](../../operations/settings/permissions-for-queries.md#settings_allow_ddl) setting is disabled.
You can’t use table functions if the [allow_ddl](../../operations/settings/permissions-for-queries.md#settings_allow_ddl) setting is disabled.
| Function | Description |
|-----------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------|

4
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@ -54,7 +54,7 @@ example01-{01..02}-1
If you have multiple pairs of curly brackets, it generates the direct product of the corresponding sets.
Addresses and parts of addresses in curly brackets can be separated by the pipe symbol (\|). In this case, the corresponding sets of addresses are interpreted as replicas, and the query will be sent to the first healthy replica. However, the replicas are iterated in the order currently set in the [load\_balancing](../../operations/settings/settings.md) setting.
Addresses and parts of addresses in curly brackets can be separated by the pipe symbol (\|). In this case, the corresponding sets of addresses are interpreted as replicas, and the query will be sent to the first healthy replica. However, the replicas are iterated in the order currently set in the [load_balancing](../../operations/settings/settings.md) setting.
Example:
@ -78,6 +78,6 @@ The `remote` table function can be useful in the following cases:
If the user is not specified, `default` is used.
If the password is not specified, an empty password is used.
`remoteSecure` - same as `remote` but with secured connection. Default port — [tcp\_port\_secure](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-tcp_port_secure) from config or 9440.
`remoteSecure` - same as `remote` but with secured connection. Default port — [tcp_port_secure](../../operations/server-configuration-parameters/settings.md#server_configuration_parameters-tcp_port_secure) from config or 9440.
[Original article](https://clickhouse.tech/docs/en/query_language/table_functions/remote/) <!--hide-->

26
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@ -157,13 +157,13 @@ This release contains bug fixes for the previous release 1.1.54276:
#### New Features: {#new-features-4}
- Added an optional WITH section for a SELECT query. Example query: `WITH 1+1 AS a SELECT a, a*a`
- INSERT can be performed synchronously in a Distributed table: OK is returned only after all the data is saved on all the shards. This is activated by the setting insert\_distributed\_sync=1.
- INSERT can be performed synchronously in a Distributed table: OK is returned only after all the data is saved on all the shards. This is activated by the setting insert_distributed_sync=1.
- Added the UUID data type for working with 16-byte identifiers.
- Added aliases of CHAR, FLOAT and other types for compatibility with the Tableau.
- Added the functions toYYYYMM, toYYYYMMDD, and toYYYYMMDDhhmmss for converting time into numbers.
- You can use IP addresses (together with the hostname) to identify servers for clustered DDL queries.
- Added support for non-constant arguments and negative offsets in the function `substring(str, pos, len).`
- Added the max\_size parameter for the `groupArray(max_size)(column)` aggregate function, and optimized its performance.
- Added the max_size parameter for the `groupArray(max_size)(column)` aggregate function, and optimized its performance.
#### Main Changes: {#main-changes}
@ -171,7 +171,7 @@ This release contains bug fixes for the previous release 1.1.54276:
- Improved error messages for queries with invalid syntax.
- Significantly reduced memory consumption and improved performance when merging large sections of MergeTree data.
- Significantly increased the performance of data merges for the ReplacingMergeTree engine.
- Improved performance for asynchronous inserts from a Distributed table by combining multiple source inserts. To enable this functionality, use the setting distributed\_directory\_monitor\_batch\_inserts=1.
- Improved performance for asynchronous inserts from a Distributed table by combining multiple source inserts. To enable this functionality, use the setting distributed_directory_monitor_batch_inserts=1.
#### Backward Incompatible Changes: {#backward-incompatible-changes-1}
@ -182,17 +182,17 @@ This release contains bug fixes for the previous release 1.1.54276:
- Added the `output_format_json_quote_denormals` setting, which enables outputting nan and inf values in JSON format.
- Optimized stream allocation when reading from a Distributed table.
- Settings can be configured in readonly mode if the value doesn’t change.
- Added the ability to retrieve non-integer granules of the MergeTree engine in order to meet restrictions on the block size specified in the preferred\_block\_size\_bytes setting. The purpose is to reduce the consumption of RAM and increase cache locality when processing queries from tables with large columns.
- Added the ability to retrieve non-integer granules of the MergeTree engine in order to meet restrictions on the block size specified in the preferred_block_size_bytes setting. The purpose is to reduce the consumption of RAM and increase cache locality when processing queries from tables with large columns.
- Efficient use of indexes that contain expressions like `toStartOfHour(x)` for conditions like `toStartOfHour(x) op сonstexpr.`
- Added new settings for MergeTree engines (the merge\_tree section in config.xml):
- replicated\_deduplication\_window\_seconds sets the number of seconds allowed for deduplicating inserts in Replicated tables.
- cleanup\_delay\_period sets how often to start cleanup to remove outdated data.
- replicated\_can\_become\_leader can prevent a replica from becoming the leader (and assigning merges).
- Added new settings for MergeTree engines (the merge_tree section in config.xml):
- replicated_deduplication_window_seconds sets the number of seconds allowed for deduplicating inserts in Replicated tables.
- cleanup_delay_period sets how often to start cleanup to remove outdated data.
- replicated_can_become_leader can prevent a replica from becoming the leader (and assigning merges).
- Accelerated cleanup to remove outdated data from ZooKeeper.
- Multiple improvements and fixes for clustered DDL queries. Of particular interest is the new setting distributed\_ddl\_task\_timeout, which limits the time to wait for a response from the servers in the cluster. If a ddl request has not been performed on all hosts, a response will contain a timeout error and a request will be executed in an async mode.
- Multiple improvements and fixes for clustered DDL queries. Of particular interest is the new setting distributed_ddl_task_timeout, which limits the time to wait for a response from the servers in the cluster. If a ddl request has not been performed on all hosts, a response will contain a timeout error and a request will be executed in an async mode.
- Improved display of stack traces in the server logs.
- Added the “none” value for the compression method.
- You can use multiple dictionaries\_config sections in config.xml.
- You can use multiple dictionaries_config sections in config.xml.
- It is possible to connect to MySQL through a socket in the file system.
- The system.parts table has a new column with information about the size of marks, in bytes.
@ -201,19 +201,19 @@ This release contains bug fixes for the previous release 1.1.54276:
- Distributed tables using a Merge table now work correctly for a SELECT query with a condition on the `_table` field.
- Fixed a rare race condition in ReplicatedMergeTree when checking data parts.
- Fixed possible freezing on “leader election” when starting a server.
- The max\_replica\_delay\_for\_distributed\_queries setting was ignored when using a local replica of the data source. This has been fixed.
- The max_replica_delay_for_distributed_queries setting was ignored when using a local replica of the data source. This has been fixed.
- Fixed incorrect behavior of `ALTER TABLE CLEAR COLUMN IN PARTITION` when attempting to clean a non-existing column.
- Fixed an exception in the multiIf function when using empty arrays or strings.
- Fixed excessive memory allocations when deserializing Native format.
- Fixed incorrect auto-update of Trie dictionaries.
- Fixed an exception when running queries with a GROUP BY clause from a Merge table when using SAMPLE.
- Fixed a crash of GROUP BY when using distributed\_aggregation\_memory\_efficient=1.
- Fixed a crash of GROUP BY when using distributed_aggregation_memory_efficient=1.
- Now you can specify the database.table in the right side of IN and JOIN.
- Too many threads were used for parallel aggregation. This has been fixed.
- Fixed how the “if” function works with FixedString arguments.
- SELECT worked incorrectly from a Distributed table for shards with a weight of 0. This has been fixed.
- Running `CREATE VIEW IF EXISTS no longer causes crashes.`
- Fixed incorrect behavior when input\_format\_skip\_unknown\_fields=1 is set and there are negative numbers.
- Fixed incorrect behavior when input_format_skip_unknown_fields=1 is set and there are negative numbers.
- Fixed an infinite loop in the `dictGetHierarchy()` function if there is some invalid data in the dictionary.
- Fixed `Syntax error: unexpected (...)` errors when running distributed queries with subqueries in an IN or JOIN clause and Merge tables.
- Fixed an incorrect interpretation of a SELECT query from Dictionary tables.

480
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@ -9,12 +9,12 @@ toc_title: '2018'
#### Bug Fixes: {#bug-fixes}
- Fixed an error that led to problems with updating dictionaries with the ODBC source. [\#3825](https://github.com/ClickHouse/ClickHouse/issues/3825), [\#3829](https://github.com/ClickHouse/ClickHouse/issues/3829)
- JIT compilation of aggregate functions now works with LowCardinality columns. [\#3838](https://github.com/ClickHouse/ClickHouse/issues/3838)
- Fixed an error that led to problems with updating dictionaries with the ODBC source. [#3825](https://github.com/ClickHouse/ClickHouse/issues/3825), [#3829](https://github.com/ClickHouse/ClickHouse/issues/3829)
- JIT compilation of aggregate functions now works with LowCardinality columns. [#3838](https://github.com/ClickHouse/ClickHouse/issues/3838)
#### Improvements: {#improvements}
- Added the `low_cardinality_allow_in_native_format` setting (enabled by default). When disabled, LowCardinality columns will be converted to ordinary columns for SELECT queries and ordinary columns will be expected for INSERT queries. [\#3879](https://github.com/ClickHouse/ClickHouse/pull/3879)
- Added the `low_cardinality_allow_in_native_format` setting (enabled by default). When disabled, LowCardinality columns will be converted to ordinary columns for SELECT queries and ordinary columns will be expected for INSERT queries. [#3879](https://github.com/ClickHouse/ClickHouse/pull/3879)
#### Build Improvements: {#build-improvements}
@ -24,79 +24,79 @@ toc_title: '2018'
#### New Features: {#new-features}
- `DEFAULT` expressions are evaluated for missing fields when loading data in semi-structured input formats (`JSONEachRow`, `TSKV`). The feature is enabled with the `insert_sample_with_metadata` setting. [\#3555](https://github.com/ClickHouse/ClickHouse/pull/3555)
- The `ALTER TABLE` query now has the `MODIFY ORDER BY` action for changing the sorting key when adding or removing a table column. This is useful for tables in the `MergeTree` family that perform additional tasks when merging based on this sorting key, such as `SummingMergeTree`, `AggregatingMergeTree`, and so on. [\#3581](https://github.com/ClickHouse/ClickHouse/pull/3581) [\#3755](https://github.com/ClickHouse/ClickHouse/pull/3755)
- For tables in the `MergeTree` family, now you can specify a different sorting key (`ORDER BY`) and index (`PRIMARY KEY`). The sorting key can be longer than the index. [\#3581](https://github.com/ClickHouse/ClickHouse/pull/3581)
- `DEFAULT` expressions are evaluated for missing fields when loading data in semi-structured input formats (`JSONEachRow`, `TSKV`). The feature is enabled with the `insert_sample_with_metadata` setting. [#3555](https://github.com/ClickHouse/ClickHouse/pull/3555)
- The `ALTER TABLE` query now has the `MODIFY ORDER BY` action for changing the sorting key when adding or removing a table column. This is useful for tables in the `MergeTree` family that perform additional tasks when merging based on this sorting key, such as `SummingMergeTree`, `AggregatingMergeTree`, and so on. [#3581](https://github.com/ClickHouse/ClickHouse/pull/3581) [#3755](https://github.com/ClickHouse/ClickHouse/pull/3755)
- For tables in the `MergeTree` family, now you can specify a different sorting key (`ORDER BY`) and index (`PRIMARY KEY`). The sorting key can be longer than the index. [#3581](https://github.com/ClickHouse/ClickHouse/pull/3581)
- Added the `hdfs` table function and the `HDFS` table engine for importing and exporting data to HDFS. [chenxing-xc](https://github.com/ClickHouse/ClickHouse/pull/3617)
- Added functions for working with base64: `base64Encode`, `base64Decode`, `tryBase64Decode`. [Alexander Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/3350)
- Now you can use a parameter to configure the precision of the `uniqCombined` aggregate function (select the number of HyperLogLog cells). [\#3406](https://github.com/ClickHouse/ClickHouse/pull/3406)
- Added the `system.contributors` table that contains the names of everyone who made commits in ClickHouse. [\#3452](https://github.com/ClickHouse/ClickHouse/pull/3452)
- Added the ability to omit the partition for the `ALTER TABLE ... FREEZE` query in order to back up all partitions at once. [\#3514](https://github.com/ClickHouse/ClickHouse/pull/3514)
- Now you can use a parameter to configure the precision of the `uniqCombined` aggregate function (select the number of HyperLogLog cells). [#3406](https://github.com/ClickHouse/ClickHouse/pull/3406)
- Added the `system.contributors` table that contains the names of everyone who made commits in ClickHouse. [#3452](https://github.com/ClickHouse/ClickHouse/pull/3452)
- Added the ability to omit the partition for the `ALTER TABLE ... FREEZE` query in order to back up all partitions at once. [#3514](https://github.com/ClickHouse/ClickHouse/pull/3514)
- Added `dictGet` and `dictGetOrDefault` functions that don’t require specifying the type of return value. The type is determined automatically from the dictionary description. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3564)
- Now you can specify comments for a column in the table description and change it using `ALTER`. [\#3377](https://github.com/ClickHouse/ClickHouse/pull/3377)
- Now you can specify comments for a column in the table description and change it using `ALTER`. [#3377](https://github.com/ClickHouse/ClickHouse/pull/3377)
- Reading is supported for `Join` type tables with simple keys. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3728)
- Now you can specify the options `join_use_nulls`, `max_rows_in_join`, `max_bytes_in_join`, and `join_overflow_mode` when creating a `Join` type table. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3728)
- Added the `joinGet` function that allows you to use a `Join` type table like a dictionary. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3728)
- Added the `partition_key`, `sorting_key`, `primary_key`, and `sampling_key` columns to the `system.tables` table in order to provide information about table keys. [\#3609](https://github.com/ClickHouse/ClickHouse/pull/3609)
- Added the `is_in_partition_key`, `is_in_sorting_key`, `is_in_primary_key`, and `is_in_sampling_key` columns to the `system.columns` table. [\#3609](https://github.com/ClickHouse/ClickHouse/pull/3609)
- Added the `partition_key`, `sorting_key`, `primary_key`, and `sampling_key` columns to the `system.tables` table in order to provide information about table keys. [#3609](https://github.com/ClickHouse/ClickHouse/pull/3609)
- Added the `is_in_partition_key`, `is_in_sorting_key`, `is_in_primary_key`, and `is_in_sampling_key` columns to the `system.columns` table. [#3609](https://github.com/ClickHouse/ClickHouse/pull/3609)
- Added the `min_time` and `max_time` columns to the `system.parts` table. These columns are populated when the partitioning key is an expression consisting of `DateTime` columns. [Emmanuel Donin de Rosière](https://github.com/ClickHouse/ClickHouse/pull/3800)
#### Bug Fixes: {#bug-fixes-1}
- Fixes and performance improvements for the `LowCardinality` data type. `GROUP BY` using `LowCardinality(Nullable(...))`. Getting the values of `extremes`. Processing high-order functions. `LEFT ARRAY JOIN`. Distributed `GROUP BY`. Functions that return `Array`. Execution of `ORDER BY`. Writing to `Distributed` tables (nicelulu). Backward compatibility for `INSERT` queries from old clients that implement the `Native` protocol. Support for `LowCardinality` for `JOIN`. Improved performance when working in a single stream. [\#3823](https://github.com/ClickHouse/ClickHouse/pull/3823) [\#3803](https://github.com/ClickHouse/ClickHouse/pull/3803) [\#3799](https://github.com/ClickHouse/ClickHouse/pull/3799) [\#3769](https://github.com/ClickHouse/ClickHouse/pull/3769) [\#3744](https://github.com/ClickHouse/ClickHouse/pull/3744) [\#3681](https://github.com/ClickHouse/ClickHouse/pull/3681) [\#3651](https://github.com/ClickHouse/ClickHouse/pull/3651) [\#3649](https://github.com/ClickHouse/ClickHouse/pull/3649) [\#3641](https://github.com/ClickHouse/ClickHouse/pull/3641) [\#3632](https://github.com/ClickHouse/ClickHouse/pull/3632) [\#3568](https://github.com/ClickHouse/ClickHouse/pull/3568) [\#3523](https://github.com/ClickHouse/ClickHouse/pull/3523) [\#3518](https://github.com/ClickHouse/ClickHouse/pull/3518)
- Fixed how the `select_sequential_consistency` option works. Previously, when this setting was enabled, an incomplete result was sometimes returned after beginning to write to a new partition. [\#2863](https://github.com/ClickHouse/ClickHouse/pull/2863)
- Databases are correctly specified when executing DDL `ON CLUSTER` queries and `ALTER UPDATE/DELETE`. [\#3772](https://github.com/ClickHouse/ClickHouse/pull/3772) [\#3460](https://github.com/ClickHouse/ClickHouse/pull/3460)
- Databases are correctly specified for subqueries inside a VIEW. [\#3521](https://github.com/ClickHouse/ClickHouse/pull/3521)
- Fixes and performance improvements for the `LowCardinality` data type. `GROUP BY` using `LowCardinality(Nullable(...))`. Getting the values of `extremes`. Processing high-order functions. `LEFT ARRAY JOIN`. Distributed `GROUP BY`. Functions that return `Array`. Execution of `ORDER BY`. Writing to `Distributed` tables (nicelulu). Backward compatibility for `INSERT` queries from old clients that implement the `Native` protocol. Support for `LowCardinality` for `JOIN`. Improved performance when working in a single stream. [#3823](https://github.com/ClickHouse/ClickHouse/pull/3823) [#3803](https://github.com/ClickHouse/ClickHouse/pull/3803) [#3799](https://github.com/ClickHouse/ClickHouse/pull/3799) [#3769](https://github.com/ClickHouse/ClickHouse/pull/3769) [#3744](https://github.com/ClickHouse/ClickHouse/pull/3744) [#3681](https://github.com/ClickHouse/ClickHouse/pull/3681) [#3651](https://github.com/ClickHouse/ClickHouse/pull/3651) [#3649](https://github.com/ClickHouse/ClickHouse/pull/3649) [#3641](https://github.com/ClickHouse/ClickHouse/pull/3641) [#3632](https://github.com/ClickHouse/ClickHouse/pull/3632) [#3568](https://github.com/ClickHouse/ClickHouse/pull/3568) [#3523](https://github.com/ClickHouse/ClickHouse/pull/3523) [#3518](https://github.com/ClickHouse/ClickHouse/pull/3518)
- Fixed how the `select_sequential_consistency` option works. Previously, when this setting was enabled, an incomplete result was sometimes returned after beginning to write to a new partition. [#2863](https://github.com/ClickHouse/ClickHouse/pull/2863)
- Databases are correctly specified when executing DDL `ON CLUSTER` queries and `ALTER UPDATE/DELETE`. [#3772](https://github.com/ClickHouse/ClickHouse/pull/3772) [#3460](https://github.com/ClickHouse/ClickHouse/pull/3460)
- Databases are correctly specified for subqueries inside a VIEW. [#3521](https://github.com/ClickHouse/ClickHouse/pull/3521)
- Fixed a bug in `PREWHERE` with `FINAL` for `VersionedCollapsingMergeTree`. [7167bfd7](https://github.com/ClickHouse/ClickHouse/commit/7167bfd7b365538f7a91c4307ad77e552ab4e8c1)
- Now you can use `KILL QUERY` to cancel queries that have not started yet because they are waiting for the table to be locked. [\#3517](https://github.com/ClickHouse/ClickHouse/pull/3517)
- Corrected date and time calculations if the clocks were moved back at midnight (this happens in Iran, and happened in Moscow from 1981 to 1983). Previously, this led to the time being reset a day earlier than necessary, and also caused incorrect formatting of the date and time in text format. [\#3819](https://github.com/ClickHouse/ClickHouse/pull/3819)
- Now you can use `KILL QUERY` to cancel queries that have not started yet because they are waiting for the table to be locked. [#3517](https://github.com/ClickHouse/ClickHouse/pull/3517)
- Corrected date and time calculations if the clocks were moved back at midnight (this happens in Iran, and happened in Moscow from 1981 to 1983). Previously, this led to the time being reset a day earlier than necessary, and also caused incorrect formatting of the date and time in text format. [#3819](https://github.com/ClickHouse/ClickHouse/pull/3819)
- Fixed bugs in some cases of `VIEW` and subqueries that omit the database. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3521)
- Fixed a race condition when simultaneously reading from a `MATERIALIZED VIEW` and deleting a `MATERIALIZED VIEW` due to not locking the internal `MATERIALIZED VIEW`. [\#3404](https://github.com/ClickHouse/ClickHouse/pull/3404) [\#3694](https://github.com/ClickHouse/ClickHouse/pull/3694)
- Fixed the error `Lock handler cannot be nullptr.` [\#3689](https://github.com/ClickHouse/ClickHouse/pull/3689)
- Fixed query processing when the `compile_expressions` option is enabled (it’s enabled by default). Nondeterministic constant expressions like the `now` function are no longer unfolded. [\#3457](https://github.com/ClickHouse/ClickHouse/pull/3457)
- Fixed a race condition when simultaneously reading from a `MATERIALIZED VIEW` and deleting a `MATERIALIZED VIEW` due to not locking the internal `MATERIALIZED VIEW`. [#3404](https://github.com/ClickHouse/ClickHouse/pull/3404) [#3694](https://github.com/ClickHouse/ClickHouse/pull/3694)
- Fixed the error `Lock handler cannot be nullptr.` [#3689](https://github.com/ClickHouse/ClickHouse/pull/3689)
- Fixed query processing when the `compile_expressions` option is enabled (it’s enabled by default). Nondeterministic constant expressions like the `now` function are no longer unfolded. [#3457](https://github.com/ClickHouse/ClickHouse/pull/3457)
- Fixed a crash when specifying a non-constant scale argument in `toDecimal32/64/128` functions.
- Fixed an error when trying to insert an array with `NULL` elements in the `Values` format into a column of type `Array` without `Nullable` (if `input_format_values_interpret_expressions` = 1). [\#3487](https://github.com/ClickHouse/ClickHouse/pull/3487) [\#3503](https://github.com/ClickHouse/ClickHouse/pull/3503)
- Fixed an error when trying to insert an array with `NULL` elements in the `Values` format into a column of type `Array` without `Nullable` (if `input_format_values_interpret_expressions` = 1). [#3487](https://github.com/ClickHouse/ClickHouse/pull/3487) [#3503](https://github.com/ClickHouse/ClickHouse/pull/3503)
- Fixed continuous error logging in `DDLWorker` if ZooKeeper is not available. [8f50c620](https://github.com/ClickHouse/ClickHouse/commit/8f50c620334988b28018213ec0092fe6423847e2)
- Fixed the return type for `quantile*` functions from `Date` and `DateTime` types of arguments. [\#3580](https://github.com/ClickHouse/ClickHouse/pull/3580)
- Fixed the `WITH` clause if it specifies a simple alias without expressions. [\#3570](https://github.com/ClickHouse/ClickHouse/pull/3570)
- Fixed the return type for `quantile*` functions from `Date` and `DateTime` types of arguments. [#3580](https://github.com/ClickHouse/ClickHouse/pull/3580)
- Fixed the `WITH` clause if it specifies a simple alias without expressions. [#3570](https://github.com/ClickHouse/ClickHouse/pull/3570)
- Fixed processing of queries with named sub-queries and qualified column names when `enable_optimize_predicate_expression` is enabled. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3588)
- Fixed the error `Attempt to attach to nullptr thread group` when working with materialized views. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3623)
- Fixed a crash when passing certain incorrect arguments to the `arrayReverse` function. [73e3a7b6](https://github.com/ClickHouse/ClickHouse/commit/73e3a7b662161d6005e7727d8a711b930386b871)
- Fixed the buffer overflow in the `extractURLParameter` function. Improved performance. Added correct processing of strings containing zero bytes. [141e9799](https://github.com/ClickHouse/ClickHouse/commit/141e9799e49201d84ea8e951d1bed4fb6d3dacb5)
- Fixed buffer overflow in the `lowerUTF8` and `upperUTF8` functions. Removed the ability to execute these functions over `FixedString` type arguments. [\#3662](https://github.com/ClickHouse/ClickHouse/pull/3662)
- Fixed a rare race condition when deleting `MergeTree` tables. [\#3680](https://github.com/ClickHouse/ClickHouse/pull/3680)
- Fixed a race condition when reading from `Buffer` tables and simultaneously performing `ALTER` or `DROP` on the target tables. [\#3719](https://github.com/ClickHouse/ClickHouse/pull/3719)
- Fixed a segfault if the `max_temporary_non_const_columns` limit was exceeded. [\#3788](https://github.com/ClickHouse/ClickHouse/pull/3788)
- Fixed buffer overflow in the `lowerUTF8` and `upperUTF8` functions. Removed the ability to execute these functions over `FixedString` type arguments. [#3662](https://github.com/ClickHouse/ClickHouse/pull/3662)
- Fixed a rare race condition when deleting `MergeTree` tables. [#3680](https://github.com/ClickHouse/ClickHouse/pull/3680)
- Fixed a race condition when reading from `Buffer` tables and simultaneously performing `ALTER` or `DROP` on the target tables. [#3719](https://github.com/ClickHouse/ClickHouse/pull/3719)
- Fixed a segfault if the `max_temporary_non_const_columns` limit was exceeded. [#3788](https://github.com/ClickHouse/ClickHouse/pull/3788)
#### Improvements: {#improvements-1}
- The server does not write the processed configuration files to the `/etc/clickhouse-server/` directory. Instead, it saves them in the `preprocessed_configs` directory inside `path`. This means that the `/etc/clickhouse-server/` directory doesn’t have write access for the `clickhouse` user, which improves security. [\#2443](https://github.com/ClickHouse/ClickHouse/pull/2443)
- The `min_merge_bytes_to_use_direct_io` option is set to 10 GiB by default. A merge that forms large parts of tables from the MergeTree family will be performed in `O_DIRECT` mode, which prevents excessive page cache eviction. [\#3504](https://github.com/ClickHouse/ClickHouse/pull/3504)
- Accelerated server start when there is a very large number of tables. [\#3398](https://github.com/ClickHouse/ClickHouse/pull/3398)
- Added a connection pool and HTTP `Keep-Alive` for connections between replicas. [\#3594](https://github.com/ClickHouse/ClickHouse/pull/3594)
- The server does not write the processed configuration files to the `/etc/clickhouse-server/` directory. Instead, it saves them in the `preprocessed_configs` directory inside `path`. This means that the `/etc/clickhouse-server/` directory doesn’t have write access for the `clickhouse` user, which improves security. [#2443](https://github.com/ClickHouse/ClickHouse/pull/2443)
- The `min_merge_bytes_to_use_direct_io` option is set to 10 GiB by default. A merge that forms large parts of tables from the MergeTree family will be performed in `O_DIRECT` mode, which prevents excessive page cache eviction. [#3504](https://github.com/ClickHouse/ClickHouse/pull/3504)
- Accelerated server start when there is a very large number of tables. [#3398](https://github.com/ClickHouse/ClickHouse/pull/3398)
- Added a connection pool and HTTP `Keep-Alive` for connections between replicas. [#3594](https://github.com/ClickHouse/ClickHouse/pull/3594)
- If the query syntax is invalid, the `400 Bad Request` code is returned in the `HTTP` interface (500 was returned previously). [31bc680a](https://github.com/ClickHouse/ClickHouse/commit/31bc680ac5f4bb1d0360a8ba4696fa84bb47d6ab)
- The `join_default_strictness` option is set to `ALL` by default for compatibility. [120e2cbe](https://github.com/ClickHouse/ClickHouse/commit/120e2cbe2ff4fbad626c28042d9b28781c805afe)
- Removed logging to `stderr` from the `re2` library for invalid or complex regular expressions. [\#3723](https://github.com/ClickHouse/ClickHouse/pull/3723)
- Added for the `Kafka` table engine: checks for subscriptions before beginning to read from Kafka; the kafka\_max\_block\_size setting for the table. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3396)
- The `cityHash64`, `farmHash64`, `metroHash64`, `sipHash64`, `halfMD5`, `murmurHash2_32`, `murmurHash2_64`, `murmurHash3_32`, and `murmurHash3_64` functions now work for any number of arguments and for arguments in the form of tuples. [\#3451](https://github.com/ClickHouse/ClickHouse/pull/3451) [\#3519](https://github.com/ClickHouse/ClickHouse/pull/3519)
- Removed logging to `stderr` from the `re2` library for invalid or complex regular expressions. [#3723](https://github.com/ClickHouse/ClickHouse/pull/3723)
- Added for the `Kafka` table engine: checks for subscriptions before beginning to read from Kafka; the kafka_max_block_size setting for the table. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3396)
- The `cityHash64`, `farmHash64`, `metroHash64`, `sipHash64`, `halfMD5`, `murmurHash2_32`, `murmurHash2_64`, `murmurHash3_32`, and `murmurHash3_64` functions now work for any number of arguments and for arguments in the form of tuples. [#3451](https://github.com/ClickHouse/ClickHouse/pull/3451) [#3519](https://github.com/ClickHouse/ClickHouse/pull/3519)
- The `arrayReverse` function now works with any types of arrays. [73e3a7b6](https://github.com/ClickHouse/ClickHouse/commit/73e3a7b662161d6005e7727d8a711b930386b871)
- Added an optional parameter: the slot size for the `timeSlots` function. [Kirill Shvakov](https://github.com/ClickHouse/ClickHouse/pull/3724)
- For `FULL` and `RIGHT JOIN`, the `max_block_size` setting is used for a stream of non-joined data from the right table. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3699)
- Added the `--secure` command line parameter in `clickhouse-benchmark` and `clickhouse-performance-test` to enable TLS. [\#3688](https://github.com/ClickHouse/ClickHouse/pull/3688) [\#3690](https://github.com/ClickHouse/ClickHouse/pull/3690)
- Added the `--secure` command line parameter in `clickhouse-benchmark` and `clickhouse-performance-test` to enable TLS. [#3688](https://github.com/ClickHouse/ClickHouse/pull/3688) [#3690](https://github.com/ClickHouse/ClickHouse/pull/3690)
- Type conversion when the structure of a `Buffer` type table does not match the structure of the destination table. [Vitaly Baranov](https://github.com/ClickHouse/ClickHouse/pull/3603)
- Added the `tcp_keep_alive_timeout` option to enable keep-alive packets after inactivity for the specified time interval. [\#3441](https://github.com/ClickHouse/ClickHouse/pull/3441)
- Removed unnecessary quoting of values for the partition key in the `system.parts` table if it consists of a single column. [\#3652](https://github.com/ClickHouse/ClickHouse/pull/3652)
- The modulo function works for `Date` and `DateTime` data types. [\#3385](https://github.com/ClickHouse/ClickHouse/pull/3385)
- Added synonyms for the `POWER`, `LN`, `LCASE`, `UCASE`, `REPLACE`, `LOCATE`, `SUBSTR`, and `MID` functions. [\#3774](https://github.com/ClickHouse/ClickHouse/pull/3774) [\#3763](https://github.com/ClickHouse/ClickHouse/pull/3763) Some function names are case-insensitive for compatibility with the SQL standard. Added syntactic sugar `SUBSTRING(expr FROM start FOR length)` for compatibility with SQL. [\#3804](https://github.com/ClickHouse/ClickHouse/pull/3804)
- Added the ability to `mlock` memory pages corresponding to `clickhouse-server` executable code to prevent it from being forced out of memory. This feature is disabled by default. [\#3553](https://github.com/ClickHouse/ClickHouse/pull/3553)
- Improved performance when reading from `O_DIRECT` (with the `min_bytes_to_use_direct_io` option enabled). [\#3405](https://github.com/ClickHouse/ClickHouse/pull/3405)
- Added the `tcp_keep_alive_timeout` option to enable keep-alive packets after inactivity for the specified time interval. [#3441](https://github.com/ClickHouse/ClickHouse/pull/3441)
- Removed unnecessary quoting of values for the partition key in the `system.parts` table if it consists of a single column. [#3652](https://github.com/ClickHouse/ClickHouse/pull/3652)
- The modulo function works for `Date` and `DateTime` data types. [#3385](https://github.com/ClickHouse/ClickHouse/pull/3385)
- Added synonyms for the `POWER`, `LN`, `LCASE`, `UCASE`, `REPLACE`, `LOCATE`, `SUBSTR`, and `MID` functions. [#3774](https://github.com/ClickHouse/ClickHouse/pull/3774) [#3763](https://github.com/ClickHouse/ClickHouse/pull/3763) Some function names are case-insensitive for compatibility with the SQL standard. Added syntactic sugar `SUBSTRING(expr FROM start FOR length)` for compatibility with SQL. [#3804](https://github.com/ClickHouse/ClickHouse/pull/3804)
- Added the ability to `mlock` memory pages corresponding to `clickhouse-server` executable code to prevent it from being forced out of memory. This feature is disabled by default. [#3553](https://github.com/ClickHouse/ClickHouse/pull/3553)
- Improved performance when reading from `O_DIRECT` (with the `min_bytes_to_use_direct_io` option enabled). [#3405](https://github.com/ClickHouse/ClickHouse/pull/3405)
- Improved performance of the `dictGet...OrDefault` function for a constant key argument and a non-constant default argument. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3563)
- The `firstSignificantSubdomain` function now processes the domains `gov`, `mil`, and `edu`. [Igor Hatarist](https://github.com/ClickHouse/ClickHouse/pull/3601) Improved performance. [\#3628](https://github.com/ClickHouse/ClickHouse/pull/3628)
- The `firstSignificantSubdomain` function now processes the domains `gov`, `mil`, and `edu`. [Igor Hatarist](https://github.com/ClickHouse/ClickHouse/pull/3601) Improved performance. [#3628](https://github.com/ClickHouse/ClickHouse/pull/3628)
- Ability to specify custom environment variables for starting `clickhouse-server` using the `SYS-V init.d` script by defining `CLICKHOUSE_PROGRAM_ENV` in `/etc/default/clickhouse`.
[Pavlo Bashynskyi](https://github.com/ClickHouse/ClickHouse/pull/3612)
- Correct return code for the clickhouse-server init script. [\#3516](https://github.com/ClickHouse/ClickHouse/pull/3516)
- The `system.metrics` table now has the `VersionInteger` metric, and `system.build_options` has the added line `VERSION_INTEGER`, which contains the numeric form of the ClickHouse version, such as `18016000`. [\#3644](https://github.com/ClickHouse/ClickHouse/pull/3644)
- Removed the ability to compare the `Date` type with a number to avoid potential errors like `date = 2018-12-17`, where quotes around the date are omitted by mistake. [\#3687](https://github.com/ClickHouse/ClickHouse/pull/3687)
- Correct return code for the clickhouse-server init script. [#3516](https://github.com/ClickHouse/ClickHouse/pull/3516)
- The `system.metrics` table now has the `VersionInteger` metric, and `system.build_options` has the added line `VERSION_INTEGER`, which contains the numeric form of the ClickHouse version, such as `18016000`. [#3644](https://github.com/ClickHouse/ClickHouse/pull/3644)
- Removed the ability to compare the `Date` type with a number to avoid potential errors like `date = 2018-12-17`, where quotes around the date are omitted by mistake. [#3687](https://github.com/ClickHouse/ClickHouse/pull/3687)
- Fixed the behavior of stateful functions like `rowNumberInAllBlocks`. They previously output a result that was one number larger due to starting during query analysis. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3729)
- If the `force_restore_data` file can’t be deleted, an error message is displayed. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3794)
@ -104,16 +104,16 @@ toc_title: '2018'
- Updated the `jemalloc` library, which fixes a potential memory leak. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3557)
- Profiling with `jemalloc` is enabled by default in order to debug builds. [2cc82f5c](https://github.com/ClickHouse/ClickHouse/commit/2cc82f5cbe266421cd4c1165286c2c47e5ffcb15)
- Added the ability to run integration tests when only `Docker` is installed on the system. [\#3650](https://github.com/ClickHouse/ClickHouse/pull/3650)
- Added the fuzz expression test in SELECT queries. [\#3442](https://github.com/ClickHouse/ClickHouse/pull/3442)
- Added a stress test for commits, which performs functional tests in parallel and in random order to detect more race conditions. [\#3438](https://github.com/ClickHouse/ClickHouse/pull/3438)
- Added the ability to run integration tests when only `Docker` is installed on the system. [#3650](https://github.com/ClickHouse/ClickHouse/pull/3650)
- Added the fuzz expression test in SELECT queries. [#3442](https://github.com/ClickHouse/ClickHouse/pull/3442)
- Added a stress test for commits, which performs functional tests in parallel and in random order to detect more race conditions. [#3438](https://github.com/ClickHouse/ClickHouse/pull/3438)
- Improved the method for starting clickhouse-server in a Docker image. [Elghazal Ahmed](https://github.com/ClickHouse/ClickHouse/pull/3663)
- For a Docker image, added support for initializing databases using files in the `/docker-entrypoint-initdb.d` directory. [Konstantin Lebedev](https://github.com/ClickHouse/ClickHouse/pull/3695)
- Fixes for builds on ARM. [\#3709](https://github.com/ClickHouse/ClickHouse/pull/3709)
- Fixes for builds on ARM. [#3709](https://github.com/ClickHouse/ClickHouse/pull/3709)
#### Backward Incompatible Changes: {#backward-incompatible-changes}
- Removed the ability to compare the `Date` type with a number. Instead of `toDate('2018-12-18') = 17883`, you must use explicit type conversion `= toDate(17883)` [\#3687](https://github.com/ClickHouse/ClickHouse/pull/3687)
- Removed the ability to compare the `Date` type with a number. Instead of `toDate('2018-12-18') = 17883`, you must use explicit type conversion `= toDate(17883)` [#3687](https://github.com/ClickHouse/ClickHouse/pull/3687)
## ClickHouse Release 18.14 {#clickhouse-release-18-14}
@ -121,9 +121,9 @@ toc_title: '2018'
#### Bug Fixes: {#bug-fixes-2}
- Fixed an error that led to problems with updating dictionaries with the ODBC source. [\#3825](https://github.com/ClickHouse/ClickHouse/issues/3825), [\#3829](https://github.com/ClickHouse/ClickHouse/issues/3829)
- Databases are correctly specified when executing DDL `ON CLUSTER` queries. [\#3460](https://github.com/ClickHouse/ClickHouse/pull/3460)
- Fixed a segfault if the `max_temporary_non_const_columns` limit was exceeded. [\#3788](https://github.com/ClickHouse/ClickHouse/pull/3788)
- Fixed an error that led to problems with updating dictionaries with the ODBC source. [#3825](https://github.com/ClickHouse/ClickHouse/issues/3825), [#3829](https://github.com/ClickHouse/ClickHouse/issues/3829)
- Databases are correctly specified when executing DDL `ON CLUSTER` queries. [#3460](https://github.com/ClickHouse/ClickHouse/pull/3460)
- Fixed a segfault if the `max_temporary_non_const_columns` limit was exceeded. [#3788](https://github.com/ClickHouse/ClickHouse/pull/3788)
#### Build Improvements: {#build-improvements-2}
@ -133,64 +133,64 @@ toc_title: '2018'
#### Bug Fixes: {#bug-fixes-3}
- Fixed error in `dictGet...` function for dictionaries of type `range`, if one of the arguments is constant and other is not. [\#3751](https://github.com/ClickHouse/ClickHouse/pull/3751)
- Fixed error that caused messages `netlink: '...': attribute type 1 has an invalid length` to be printed in Linux kernel log, that was happening only on fresh enough versions of Linux kernel. [\#3749](https://github.com/ClickHouse/ClickHouse/pull/3749)
- Fixed error in `dictGet...` function for dictionaries of type `range`, if one of the arguments is constant and other is not. [#3751](https://github.com/ClickHouse/ClickHouse/pull/3751)
- Fixed error that caused messages `netlink: '...': attribute type 1 has an invalid length` to be printed in Linux kernel log, that was happening only on fresh enough versions of Linux kernel. [#3749](https://github.com/ClickHouse/ClickHouse/pull/3749)
- Fixed segfault in function `empty` for argument of `FixedString` type. [Daniel, Dao Quang Minh](https://github.com/ClickHouse/ClickHouse/pull/3703)
- Fixed excessive memory allocation when using large value of `max_query_size` setting (a memory chunk of `max_query_size` bytes was preallocated at once). [\#3720](https://github.com/ClickHouse/ClickHouse/pull/3720)
- Fixed excessive memory allocation when using large value of `max_query_size` setting (a memory chunk of `max_query_size` bytes was preallocated at once). [#3720](https://github.com/ClickHouse/ClickHouse/pull/3720)
#### Build Changes: {#build-changes}
- Fixed build with LLVM/Clang libraries of version 7 from the OS packages (these libraries are used for runtime query compilation). [\#3582](https://github.com/ClickHouse/ClickHouse/pull/3582)
- Fixed build with LLVM/Clang libraries of version 7 from the OS packages (these libraries are used for runtime query compilation). [#3582](https://github.com/ClickHouse/ClickHouse/pull/3582)
### ClickHouse Release 18.14.17, 2018-11-30 {#clickhouse-release-18-14-17-2018-11-30}
#### Bug Fixes: {#bug-fixes-4}
- Fixed cases when the ODBC bridge process did not terminate with the main server process. [\#3642](https://github.com/ClickHouse/ClickHouse/pull/3642)
- Fixed synchronous insertion into the `Distributed` table with a columns list that differs from the column list of the remote table. [\#3673](https://github.com/ClickHouse/ClickHouse/pull/3673)
- Fixed a rare race condition that can lead to a crash when dropping a MergeTree table. [\#3643](https://github.com/ClickHouse/ClickHouse/pull/3643)
- Fixed a query deadlock in case when query thread creation fails with the `Resource temporarily unavailable` error. [\#3643](https://github.com/ClickHouse/ClickHouse/pull/3643)
- Fixed parsing of the `ENGINE` clause when the `CREATE AS table` syntax was used and the `ENGINE` clause was specified before the `AS table` (the error resulted in ignoring the specified engine). [\#3692](https://github.com/ClickHouse/ClickHouse/pull/3692)
- Fixed cases when the ODBC bridge process did not terminate with the main server process. [#3642](https://github.com/ClickHouse/ClickHouse/pull/3642)
- Fixed synchronous insertion into the `Distributed` table with a columns list that differs from the column list of the remote table. [#3673](https://github.com/ClickHouse/ClickHouse/pull/3673)
- Fixed a rare race condition that can lead to a crash when dropping a MergeTree table. [#3643](https://github.com/ClickHouse/ClickHouse/pull/3643)
- Fixed a query deadlock in case when query thread creation fails with the `Resource temporarily unavailable` error. [#3643](https://github.com/ClickHouse/ClickHouse/pull/3643)
- Fixed parsing of the `ENGINE` clause when the `CREATE AS table` syntax was used and the `ENGINE` clause was specified before the `AS table` (the error resulted in ignoring the specified engine). [#3692](https://github.com/ClickHouse/ClickHouse/pull/3692)
### ClickHouse Release 18.14.15, 2018-11-21 {#clickhouse-release-18-14-15-2018-11-21}
#### Bug Fixes: {#bug-fixes-5}
- The size of memory chunk was overestimated while deserializing the column of type `Array(String)` that leads to “Memory limit exceeded” errors. The issue appeared in version 18.12.13. [\#3589](https://github.com/ClickHouse/ClickHouse/issues/3589)
- The size of memory chunk was overestimated while deserializing the column of type `Array(String)` that leads to “Memory limit exceeded” errors. The issue appeared in version 18.12.13. [#3589](https://github.com/ClickHouse/ClickHouse/issues/3589)
### ClickHouse Release 18.14.14, 2018-11-20 {#clickhouse-release-18-14-14-2018-11-20}
#### Bug Fixes: {#bug-fixes-6}
- Fixed `ON CLUSTER` queries when cluster configured as secure (flag `<secure>`). [\#3599](https://github.com/ClickHouse/ClickHouse/pull/3599)
- Fixed `ON CLUSTER` queries when cluster configured as secure (flag `<secure>`). [#3599](https://github.com/ClickHouse/ClickHouse/pull/3599)
#### Build Changes: {#build-changes-1}
- Fixed problems (llvm-7 from system, macos) [\#3582](https://github.com/ClickHouse/ClickHouse/pull/3582)
- Fixed problems (llvm-7 from system, macos) [#3582](https://github.com/ClickHouse/ClickHouse/pull/3582)
### ClickHouse Release 18.14.13, 2018-11-08 {#clickhouse-release-18-14-13-2018-11-08}
#### Bug Fixes: {#bug-fixes-7}
- Fixed the `Block structure mismatch in MergingSorted stream` error. [\#3162](https://github.com/ClickHouse/ClickHouse/issues/3162)
- Fixed `ON CLUSTER` queries in case when secure connections were turned on in the cluster config (the `<secure>` flag). [\#3465](https://github.com/ClickHouse/ClickHouse/pull/3465)
- Fixed an error in queries that used `SAMPLE`, `PREWHERE` and alias columns. [\#3543](https://github.com/ClickHouse/ClickHouse/pull/3543)
- Fixed the `Block structure mismatch in MergingSorted stream` error. [#3162](https://github.com/ClickHouse/ClickHouse/issues/3162)
- Fixed `ON CLUSTER` queries in case when secure connections were turned on in the cluster config (the `<secure>` flag). [#3465](https://github.com/ClickHouse/ClickHouse/pull/3465)
- Fixed an error in queries that used `SAMPLE`, `PREWHERE` and alias columns. [#3543](https://github.com/ClickHouse/ClickHouse/pull/3543)
- Fixed a rare `unknown compression method` error when the `min_bytes_to_use_direct_io` setting was enabled. [3544](https://github.com/ClickHouse/ClickHouse/pull/3544)
#### Performance Improvements: {#performance-improvements}
- Fixed performance regression of queries with `GROUP BY` of columns of UInt16 or Date type when executing on AMD EPYC processors. [Igor Lapko](https://github.com/ClickHouse/ClickHouse/pull/3512)
- Fixed performance regression of queries that process long strings. [\#3530](https://github.com/ClickHouse/ClickHouse/pull/3530)
- Fixed performance regression of queries that process long strings. [#3530](https://github.com/ClickHouse/ClickHouse/pull/3530)
#### Build Improvements: {#build-improvements-3}
- Improvements for simplifying the Arcadia build. [\#3475](https://github.com/ClickHouse/ClickHouse/pull/3475), [\#3535](https://github.com/ClickHouse/ClickHouse/pull/3535)
- Improvements for simplifying the Arcadia build. [#3475](https://github.com/ClickHouse/ClickHouse/pull/3475), [#3535](https://github.com/ClickHouse/ClickHouse/pull/3535)
### ClickHouse Release 18.14.12, 2018-11-02 {#clickhouse-release-18-14-12-2018-11-02}
#### Bug Fixes: {#bug-fixes-8}
- Fixed a crash on joining two unnamed subqueries. [\#3505](https://github.com/ClickHouse/ClickHouse/pull/3505)
- Fixed a crash on joining two unnamed subqueries. [#3505](https://github.com/ClickHouse/ClickHouse/pull/3505)
- Fixed generating incorrect queries (with an empty `WHERE` clause) when querying external databases. [hotid](https://github.com/ClickHouse/ClickHouse/pull/3477)
- Fixed using an incorrect timeout value in ODBC dictionaries. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3511)
@ -198,106 +198,106 @@ toc_title: '2018'
#### Bug Fixes: {#bug-fixes-9}
- Fixed the error `Block structure mismatch in UNION stream: different number of columns` in LIMIT queries. [\#2156](https://github.com/ClickHouse/ClickHouse/issues/2156)
- Fixed errors when merging data in tables containing arrays inside Nested structures. [\#3397](https://github.com/ClickHouse/ClickHouse/pull/3397)
- Fixed incorrect query results if the `merge_tree_uniform_read_distribution` setting is disabled (it is enabled by default). [\#3429](https://github.com/ClickHouse/ClickHouse/pull/3429)
- Fixed an error on inserts to a Distributed table in Native format. [\#3411](https://github.com/ClickHouse/ClickHouse/issues/3411)
- Fixed the error `Block structure mismatch in UNION stream: different number of columns` in LIMIT queries. [#2156](https://github.com/ClickHouse/ClickHouse/issues/2156)
- Fixed errors when merging data in tables containing arrays inside Nested structures. [#3397](https://github.com/ClickHouse/ClickHouse/pull/3397)
- Fixed incorrect query results if the `merge_tree_uniform_read_distribution` setting is disabled (it is enabled by default). [#3429](https://github.com/ClickHouse/ClickHouse/pull/3429)
- Fixed an error on inserts to a Distributed table in Native format. [#3411](https://github.com/ClickHouse/ClickHouse/issues/3411)
### ClickHouse Release 18.14.10, 2018-10-23 {#clickhouse-release-18-14-10-2018-10-23}
- The `compile_expressions` setting (JIT compilation of expressions) is disabled by default. [\#3410](https://github.com/ClickHouse/ClickHouse/pull/3410)
- The `compile_expressions` setting (JIT compilation of expressions) is disabled by default. [#3410](https://github.com/ClickHouse/ClickHouse/pull/3410)
- The `enable_optimize_predicate_expression` setting is disabled by default.
### ClickHouse Release 18.14.9, 2018-10-16 {#clickhouse-release-18-14-9-2018-10-16}
#### New Features: {#new-features-1}
- The `WITH CUBE` modifier for `GROUP BY` (the alternative syntax `GROUP BY CUBE(...)` is also available). [\#3172](https://github.com/ClickHouse/ClickHouse/pull/3172)
- The `WITH CUBE` modifier for `GROUP BY` (the alternative syntax `GROUP BY CUBE(...)` is also available). [#3172](https://github.com/ClickHouse/ClickHouse/pull/3172)
- Added the `formatDateTime` function. [Alexandr Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/2770)
- Added the `JDBC` table engine and `jdbc` table function (requires installing clickhouse-jdbc-bridge). [Alexandr Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/3210)
- Added functions for working with the ISO week number: `toISOWeek`, `toISOYear`, `toStartOfISOYear`, and `toDayOfYear`. [\#3146](https://github.com/ClickHouse/ClickHouse/pull/3146)
- Now you can use `Nullable` columns for `MySQL` and `ODBC` tables. [\#3362](https://github.com/ClickHouse/ClickHouse/pull/3362)
- Added functions for working with the ISO week number: `toISOWeek`, `toISOYear`, `toStartOfISOYear`, and `toDayOfYear`. [#3146](https://github.com/ClickHouse/ClickHouse/pull/3146)
- Now you can use `Nullable` columns for `MySQL` and `ODBC` tables. [#3362](https://github.com/ClickHouse/ClickHouse/pull/3362)
- Nested data structures can be read as nested objects in `JSONEachRow` format. Added the `input_format_import_nested_json` setting. [Veloman Yunkan](https://github.com/ClickHouse/ClickHouse/pull/3144)
- Parallel processing is available for many `MATERIALIZED VIEW`s when inserting data. See the `parallel_view_processing` setting. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3208)
- Added the `SYSTEM FLUSH LOGS` query (forced log flushes to system tables such as `query_log`) [\#3321](https://github.com/ClickHouse/ClickHouse/pull/3321)
- Now you can use pre-defined `database` and `table` macros when declaring `Replicated` tables. [\#3251](https://github.com/ClickHouse/ClickHouse/pull/3251)
- Added the ability to read `Decimal` type values in engineering notation (indicating powers of ten). [\#3153](https://github.com/ClickHouse/ClickHouse/pull/3153)
- Added the `SYSTEM FLUSH LOGS` query (forced log flushes to system tables such as `query_log`) [#3321](https://github.com/ClickHouse/ClickHouse/pull/3321)
- Now you can use pre-defined `database` and `table` macros when declaring `Replicated` tables. [#3251](https://github.com/ClickHouse/ClickHouse/pull/3251)
- Added the ability to read `Decimal` type values in engineering notation (indicating powers of ten). [#3153](https://github.com/ClickHouse/ClickHouse/pull/3153)
#### Experimental Features: {#experimental-features}
- Optimization of the GROUP BY clause for `LowCardinality data types.` [\#3138](https://github.com/ClickHouse/ClickHouse/pull/3138)
- Optimized calculation of expressions for `LowCardinality data types.` [\#3200](https://github.com/ClickHouse/ClickHouse/pull/3200)
- Optimization of the GROUP BY clause for `LowCardinality data types.` [#3138](https://github.com/ClickHouse/ClickHouse/pull/3138)
- Optimized calculation of expressions for `LowCardinality data types.` [#3200](https://github.com/ClickHouse/ClickHouse/pull/3200)
#### Improvements: {#improvements-2}
- Significantly reduced memory consumption for queries with `ORDER BY` and `LIMIT`. See the `max_bytes_before_remerge_sort` setting. [\#3205](https://github.com/ClickHouse/ClickHouse/pull/3205)
- In the absence of `JOIN` (`LEFT`, `INNER`, …), `INNER JOIN` is assumed. [\#3147](https://github.com/ClickHouse/ClickHouse/pull/3147)
- Significantly reduced memory consumption for queries with `ORDER BY` and `LIMIT`. See the `max_bytes_before_remerge_sort` setting. [#3205](https://github.com/ClickHouse/ClickHouse/pull/3205)
- In the absence of `JOIN` (`LEFT`, `INNER`, …), `INNER JOIN` is assumed. [#3147](https://github.com/ClickHouse/ClickHouse/pull/3147)
- Qualified asterisks work correctly in queries with `JOIN`. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3202)
- The `ODBC` table engine correctly chooses the method for quoting identifiers in the SQL dialect of a remote database. [Alexandr Krasheninnikov](https://github.com/ClickHouse/ClickHouse/pull/3210)
- The `compile_expressions` setting (JIT compilation of expressions) is enabled by default.
- Fixed behavior for simultaneous DROP DATABASE/TABLE IF EXISTS and CREATE DATABASE/TABLE IF NOT EXISTS. Previously, a `CREATE DATABASE ... IF NOT EXISTS` query could return the error message “File … already exists”, and the `CREATE TABLE ... IF NOT EXISTS` and `DROP TABLE IF EXISTS` queries could return `Table ... is creating or attaching right now`. [\#3101](https://github.com/ClickHouse/ClickHouse/pull/3101)
- LIKE and IN expressions with a constant right half are passed to the remote server when querying from MySQL or ODBC tables. [\#3182](https://github.com/ClickHouse/ClickHouse/pull/3182)
- Comparisons with constant expressions in a WHERE clause are passed to the remote server when querying from MySQL and ODBC tables. Previously, only comparisons with constants were passed. [\#3182](https://github.com/ClickHouse/ClickHouse/pull/3182)
- Fixed behavior for simultaneous DROP DATABASE/TABLE IF EXISTS and CREATE DATABASE/TABLE IF NOT EXISTS. Previously, a `CREATE DATABASE ... IF NOT EXISTS` query could return the error message “File … already exists”, and the `CREATE TABLE ... IF NOT EXISTS` and `DROP TABLE IF EXISTS` queries could return `Table ... is creating or attaching right now`. [#3101](https://github.com/ClickHouse/ClickHouse/pull/3101)
- LIKE and IN expressions with a constant right half are passed to the remote server when querying from MySQL or ODBC tables. [#3182](https://github.com/ClickHouse/ClickHouse/pull/3182)
- Comparisons with constant expressions in a WHERE clause are passed to the remote server when querying from MySQL and ODBC tables. Previously, only comparisons with constants were passed. [#3182](https://github.com/ClickHouse/ClickHouse/pull/3182)
- Correct calculation of row width in the terminal for `Pretty` formats, including strings with hieroglyphs. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/3257).
- `ON CLUSTER` can be specified for `ALTER UPDATE` queries.
- Improved performance for reading data in `JSONEachRow` format. [\#3332](https://github.com/ClickHouse/ClickHouse/pull/3332)
- Added synonyms for the `LENGTH` and `CHARACTER_LENGTH` functions for compatibility. The `CONCAT` function is no longer case-sensitive. [\#3306](https://github.com/ClickHouse/ClickHouse/pull/3306)
- Added the `TIMESTAMP` synonym for the `DateTime` type. [\#3390](https://github.com/ClickHouse/ClickHouse/pull/3390)
- There is always space reserved for query\_id in the server logs, even if the log line is not related to a query. This makes it easier to parse server text logs with third-party tools.
- Memory consumption by a query is logged when it exceeds the next level of an integer number of gigabytes. [\#3205](https://github.com/ClickHouse/ClickHouse/pull/3205)
- Added compatibility mode for the case when the client library that uses the Native protocol sends fewer columns by mistake than the server expects for the INSERT query. This scenario was possible when using the clickhouse-cpp library. Previously, this scenario caused the server to crash. [\#3171](https://github.com/ClickHouse/ClickHouse/pull/3171)
- In a user-defined WHERE expression in `clickhouse-copier`, you can now use a `partition_key` alias (for additional filtering by source table partition). This is useful if the partitioning scheme changes during copying, but only changes slightly. [\#3166](https://github.com/ClickHouse/ClickHouse/pull/3166)
- Improved performance for reading data in `JSONEachRow` format. [#3332](https://github.com/ClickHouse/ClickHouse/pull/3332)
- Added synonyms for the `LENGTH` and `CHARACTER_LENGTH` functions for compatibility. The `CONCAT` function is no longer case-sensitive. [#3306](https://github.com/ClickHouse/ClickHouse/pull/3306)
- Added the `TIMESTAMP` synonym for the `DateTime` type. [#3390](https://github.com/ClickHouse/ClickHouse/pull/3390)
- There is always space reserved for query_id in the server logs, even if the log line is not related to a query. This makes it easier to parse server text logs with third-party tools.
- Memory consumption by a query is logged when it exceeds the next level of an integer number of gigabytes. [#3205](https://github.com/ClickHouse/ClickHouse/pull/3205)
- Added compatibility mode for the case when the client library that uses the Native protocol sends fewer columns by mistake than the server expects for the INSERT query. This scenario was possible when using the clickhouse-cpp library. Previously, this scenario caused the server to crash. [#3171](https://github.com/ClickHouse/ClickHouse/pull/3171)
- In a user-defined WHERE expression in `clickhouse-copier`, you can now use a `partition_key` alias (for additional filtering by source table partition). This is useful if the partitioning scheme changes during copying, but only changes slightly. [#3166](https://github.com/ClickHouse/ClickHouse/pull/3166)
- The workflow of the `Kafka` engine has been moved to a background thread pool in order to automatically reduce the speed of data reading at high loads. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3215).
- Support for reading `Tuple` and `Nested` values of structures like `struct` in the `Cap'n'Proto format`. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3216)
- The list of top-level domains for the `firstSignificantSubdomain` function now includes the domain `biz`. [decaseal](https://github.com/ClickHouse/ClickHouse/pull/3219)
- In the configuration of external dictionaries, `null_value` is interpreted as the value of the default data type. [\#3330](https://github.com/ClickHouse/ClickHouse/pull/3330)
- In the configuration of external dictionaries, `null_value` is interpreted as the value of the default data type. [#3330](https://github.com/ClickHouse/ClickHouse/pull/3330)
- Support for the `intDiv` and `intDivOrZero` functions for `Decimal`. [b48402e8](https://github.com/ClickHouse/ClickHouse/commit/b48402e8712e2b9b151e0eef8193811d433a1264)
- Support for the `Date`, `DateTime`, `UUID`, and `Decimal` types as a key for the `sumMap` aggregate function. [\#3281](https://github.com/ClickHouse/ClickHouse/pull/3281)
- Support for the `Decimal` data type in external dictionaries. [\#3324](https://github.com/ClickHouse/ClickHouse/pull/3324)
- Support for the `Decimal` data type in `SummingMergeTree` tables. [\#3348](https://github.com/ClickHouse/ClickHouse/pull/3348)
- Added specializations for `UUID` in `if`. [\#3366](https://github.com/ClickHouse/ClickHouse/pull/3366)
- Reduced the number of `open` and `close` system calls when reading from a `MergeTree table`. [\#3283](https://github.com/ClickHouse/ClickHouse/pull/3283)
- Support for the `Date`, `DateTime`, `UUID`, and `Decimal` types as a key for the `sumMap` aggregate function. [#3281](https://github.com/ClickHouse/ClickHouse/pull/3281)
- Support for the `Decimal` data type in external dictionaries. [#3324](https://github.com/ClickHouse/ClickHouse/pull/3324)
- Support for the `Decimal` data type in `SummingMergeTree` tables. [#3348](https://github.com/ClickHouse/ClickHouse/pull/3348)
- Added specializations for `UUID` in `if`. [#3366](https://github.com/ClickHouse/ClickHouse/pull/3366)
- Reduced the number of `open` and `close` system calls when reading from a `MergeTree table`. [#3283](https://github.com/ClickHouse/ClickHouse/pull/3283)
- A `TRUNCATE TABLE` query can be executed on any replica (the query is passed to the leader replica). [Kirill Shvakov](https://github.com/ClickHouse/ClickHouse/pull/3375)
#### Bug Fixes: {#bug-fixes-10}
- Fixed an issue with `Dictionary` tables for `range_hashed` dictionaries. This error occurred in version 18.12.17. [\#1702](https://github.com/ClickHouse/ClickHouse/pull/1702)
- Fixed an error when loading `range_hashed` dictionaries (the message `Unsupported type Nullable (...)`). This error occurred in version 18.12.17. [\#3362](https://github.com/ClickHouse/ClickHouse/pull/3362)
- Fixed errors in the `pointInPolygon` function due to the accumulation of inaccurate calculations for polygons with a large number of vertices located close to each other. [\#3331](https://github.com/ClickHouse/ClickHouse/pull/3331) [\#3341](https://github.com/ClickHouse/ClickHouse/pull/3341)
- If after merging data parts, the checksum for the resulting part differs from the result of the same merge in another replica, the result of the merge is deleted and the data part is downloaded from the other replica (this is the correct behavior). But after downloading the data part, it couldn’t be added to the working set because of an error that the part already exists (because the data part was deleted with some delay after the merge). This led to cyclical attempts to download the same data. [\#3194](https://github.com/ClickHouse/ClickHouse/pull/3194)
- Fixed an issue with `Dictionary` tables for `range_hashed` dictionaries. This error occurred in version 18.12.17. [#1702](https://github.com/ClickHouse/ClickHouse/pull/1702)
- Fixed an error when loading `range_hashed` dictionaries (the message `Unsupported type Nullable (...)`). This error occurred in version 18.12.17. [#3362](https://github.com/ClickHouse/ClickHouse/pull/3362)
- Fixed errors in the `pointInPolygon` function due to the accumulation of inaccurate calculations for polygons with a large number of vertices located close to each other. [#3331](https://github.com/ClickHouse/ClickHouse/pull/3331) [#3341](https://github.com/ClickHouse/ClickHouse/pull/3341)
- If after merging data parts, the checksum for the resulting part differs from the result of the same merge in another replica, the result of the merge is deleted and the data part is downloaded from the other replica (this is the correct behavior). But after downloading the data part, it couldn’t be added to the working set because of an error that the part already exists (because the data part was deleted with some delay after the merge). This led to cyclical attempts to download the same data. [#3194](https://github.com/ClickHouse/ClickHouse/pull/3194)
- Fixed incorrect calculation of total memory consumption by queries (because of incorrect calculation, the `max_memory_usage_for_all_queries` setting worked incorrectly and the `MemoryTracking` metric had an incorrect value). This error occurred in version 18.12.13. [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3344)
- Fixed the functionality of `CREATE TABLE ... ON CLUSTER ... AS SELECT ...` This error occurred in version 18.12.13. [\#3247](https://github.com/ClickHouse/ClickHouse/pull/3247)
- Fixed unnecessary preparation of data structures for `JOIN`s on the server that initiates the query if the `JOIN` is only performed on remote servers. [\#3340](https://github.com/ClickHouse/ClickHouse/pull/3340)
- Fixed the functionality of `CREATE TABLE ... ON CLUSTER ... AS SELECT ...` This error occurred in version 18.12.13. [#3247](https://github.com/ClickHouse/ClickHouse/pull/3247)
- Fixed unnecessary preparation of data structures for `JOIN`s on the server that initiates the query if the `JOIN` is only performed on remote servers. [#3340](https://github.com/ClickHouse/ClickHouse/pull/3340)
- Fixed bugs in the `Kafka` engine: deadlocks after exceptions when starting to read data, and locks upon completion [Marek Vavruša](https://github.com/ClickHouse/ClickHouse/pull/3215).
- For `Kafka` tables, the optional `schema` parameter was not passed (the schema of the `Cap'n'Proto` format). [Vojtech Splichal](https://github.com/ClickHouse/ClickHouse/pull/3150)
- If the ensemble of ZooKeeper servers has servers that accept the connection but then immediately close it instead of responding to the handshake, ClickHouse chooses to connect another server. Previously, this produced the error `Cannot read all data. Bytes read: 0. Bytes expected: 4.` and the server couldn’t start. [8218cf3a](https://github.com/ClickHouse/ClickHouse/commit/8218cf3a5f39a43401953769d6d12a0bb8d29da9)
- If the ensemble of ZooKeeper servers contains servers for which the DNS query returns an error, these servers are ignored. [17b8e209](https://github.com/ClickHouse/ClickHouse/commit/17b8e209221061325ad7ba0539f03c6e65f87f29)
- Fixed type conversion between `Date` and `DateTime` when inserting data in the `VALUES` format (if `input_format_values_interpret_expressions = 1`). Previously, the conversion was performed between the numerical value of the number of days in Unix Epoch time and the Unix timestamp, which led to unexpected results. [\#3229](https://github.com/ClickHouse/ClickHouse/pull/3229)
- Corrected type conversion between `Decimal` and integer numbers. [\#3211](https://github.com/ClickHouse/ClickHouse/pull/3211)
- Fixed type conversion between `Date` and `DateTime` when inserting data in the `VALUES` format (if `input_format_values_interpret_expressions = 1`). Previously, the conversion was performed between the numerical value of the number of days in Unix Epoch time and the Unix timestamp, which led to unexpected results. [#3229](https://github.com/ClickHouse/ClickHouse/pull/3229)
- Corrected type conversion between `Decimal` and integer numbers. [#3211](https://github.com/ClickHouse/ClickHouse/pull/3211)
- Fixed errors in the `enable_optimize_predicate_expression` setting. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3231)
- Fixed a parsing error in CSV format with floating-point numbers if a non-default CSV separator is used, such as `;` [\#3155](https://github.com/ClickHouse/ClickHouse/pull/3155)
- Fixed a parsing error in CSV format with floating-point numbers if a non-default CSV separator is used, such as `;` [#3155](https://github.com/ClickHouse/ClickHouse/pull/3155)
- Fixed the `arrayCumSumNonNegative` function (it does not accumulate negative values if the accumulator is less than zero). [Aleksey Studnev](https://github.com/ClickHouse/ClickHouse/pull/3163)
- Fixed how `Merge` tables work on top of `Distributed` tables when using `PREWHERE`. [\#3165](https://github.com/ClickHouse/ClickHouse/pull/3165)
- Fixed how `Merge` tables work on top of `Distributed` tables when using `PREWHERE`. [#3165](https://github.com/ClickHouse/ClickHouse/pull/3165)
- Bug fixes in the `ALTER UPDATE` query.
- Fixed bugs in the `odbc` table function that appeared in version 18.12. [\#3197](https://github.com/ClickHouse/ClickHouse/pull/3197)
- Fixed the operation of aggregate functions with `StateArray` combinators. [\#3188](https://github.com/ClickHouse/ClickHouse/pull/3188)
- Fixed bugs in the `odbc` table function that appeared in version 18.12. [#3197](https://github.com/ClickHouse/ClickHouse/pull/3197)
- Fixed the operation of aggregate functions with `StateArray` combinators. [#3188](https://github.com/ClickHouse/ClickHouse/pull/3188)
- Fixed a crash when dividing a `Decimal` value by zero. [69dd6609](https://github.com/ClickHouse/ClickHouse/commit/69dd6609193beb4e7acd3e6ad216eca0ccfb8179)
- Fixed output of types for operations using `Decimal` and integer arguments. [\#3224](https://github.com/ClickHouse/ClickHouse/pull/3224)
- Fixed output of types for operations using `Decimal` and integer arguments. [#3224](https://github.com/ClickHouse/ClickHouse/pull/3224)
- Fixed the segfault during `GROUP BY` on `Decimal128`. [3359ba06](https://github.com/ClickHouse/ClickHouse/commit/3359ba06c39fcd05bfdb87d6c64154819621e13a)
- The `log_query_threads` setting (logging information about each thread of query execution) now takes effect only if the `log_queries` option (logging information about queries) is set to 1. Since the `log_query_threads` option is enabled by default, information about threads was previously logged even if query logging was disabled. [\#3241](https://github.com/ClickHouse/ClickHouse/pull/3241)
- The `log_query_threads` setting (logging information about each thread of query execution) now takes effect only if the `log_queries` option (logging information about queries) is set to 1. Since the `log_query_threads` option is enabled by default, information about threads was previously logged even if query logging was disabled. [#3241](https://github.com/ClickHouse/ClickHouse/pull/3241)
- Fixed an error in the distributed operation of the quantiles aggregate function (the error message `Not found column quantile...`). [292a8855](https://github.com/ClickHouse/ClickHouse/commit/292a885533b8e3b41ce8993867069d14cbd5a664)
- Fixed the compatibility problem when working on a cluster of version 18.12.17 servers and older servers at the same time. For distributed queries with GROUP BY keys of both fixed and non-fixed length, if there was a large amount of data to aggregate, the returned data was not always fully aggregated (two different rows contained the same aggregation keys). [\#3254](https://github.com/ClickHouse/ClickHouse/pull/3254)
- Fixed handling of substitutions in `clickhouse-performance-test`, if the query contains only part of the substitutions declared in the test. [\#3263](https://github.com/ClickHouse/ClickHouse/pull/3263)
- Fixed an error when using `FINAL` with `PREWHERE`. [\#3298](https://github.com/ClickHouse/ClickHouse/pull/3298)
- Fixed an error when using `PREWHERE` over columns that were added during `ALTER`. [\#3298](https://github.com/ClickHouse/ClickHouse/pull/3298)
- Added a check for the absence of `arrayJoin` for `DEFAULT` and `MATERIALIZED` expressions. Previously, `arrayJoin` led to an error when inserting data. [\#3337](https://github.com/ClickHouse/ClickHouse/pull/3337)
- Added a check for the absence of `arrayJoin` in a `PREWHERE` clause. Previously, this led to messages like `Size ... doesn't match` or `Unknown compression method` when executing queries. [\#3357](https://github.com/ClickHouse/ClickHouse/pull/3357)
- Fixed the compatibility problem when working on a cluster of version 18.12.17 servers and older servers at the same time. For distributed queries with GROUP BY keys of both fixed and non-fixed length, if there was a large amount of data to aggregate, the returned data was not always fully aggregated (two different rows contained the same aggregation keys). [#3254](https://github.com/ClickHouse/ClickHouse/pull/3254)
- Fixed handling of substitutions in `clickhouse-performance-test`, if the query contains only part of the substitutions declared in the test. [#3263](https://github.com/ClickHouse/ClickHouse/pull/3263)
- Fixed an error when using `FINAL` with `PREWHERE`. [#3298](https://github.com/ClickHouse/ClickHouse/pull/3298)
- Fixed an error when using `PREWHERE` over columns that were added during `ALTER`. [#3298](https://github.com/ClickHouse/ClickHouse/pull/3298)
- Added a check for the absence of `arrayJoin` for `DEFAULT` and `MATERIALIZED` expressions. Previously, `arrayJoin` led to an error when inserting data. [#3337](https://github.com/ClickHouse/ClickHouse/pull/3337)
- Added a check for the absence of `arrayJoin` in a `PREWHERE` clause. Previously, this led to messages like `Size ... doesn't match` or `Unknown compression method` when executing queries. [#3357](https://github.com/ClickHouse/ClickHouse/pull/3357)
- Fixed segfault that could occur in rare cases after optimization that replaced AND chains from equality evaluations with the corresponding IN expression. [liuyimin-bytedance](https://github.com/ClickHouse/ClickHouse/pull/3339)
- Minor corrections to `clickhouse-benchmark`: previously, client information was not sent to the server; now the number of queries executed is calculated more accurately when shutting down and for limiting the number of iterations. [\#3351](https://github.com/ClickHouse/ClickHouse/pull/3351) [\#3352](https://github.com/ClickHouse/ClickHouse/pull/3352)
- Minor corrections to `clickhouse-benchmark`: previously, client information was not sent to the server; now the number of queries executed is calculated more accurately when shutting down and for limiting the number of iterations. [#3351](https://github.com/ClickHouse/ClickHouse/pull/3351) [#3352](https://github.com/ClickHouse/ClickHouse/pull/3352)
#### Backward Incompatible Changes: {#backward-incompatible-changes-1}
- Removed the `allow_experimental_decimal_type` option. The `Decimal` data type is available for default use. [\#3329](https://github.com/ClickHouse/ClickHouse/pull/3329)
- Removed the `allow_experimental_decimal_type` option. The `Decimal` data type is available for default use. [#3329](https://github.com/ClickHouse/ClickHouse/pull/3329)
## ClickHouse Release 18.12 {#clickhouse-release-18-12}
@ -305,18 +305,18 @@ toc_title: '2018'
#### New Features: {#new-features-2}
- `invalidate_query` (the ability to specify a query to check whether an external dictionary needs to be updated) is implemented for the `clickhouse` source. [\#3126](https://github.com/ClickHouse/ClickHouse/pull/3126)
- `invalidate_query` (the ability to specify a query to check whether an external dictionary needs to be updated) is implemented for the `clickhouse` source. [#3126](https://github.com/ClickHouse/ClickHouse/pull/3126)
- Added the ability to use `UInt*`, `Int*`, and `DateTime` data types (along with the `Date` type) as a `range_hashed` external dictionary key that defines the boundaries of ranges. Now `NULL` can be used to designate an open range. [Vasily Nemkov](https://github.com/ClickHouse/ClickHouse/pull/3123)
- The `Decimal` type now supports `var*` and `stddev*` aggregate functions. [\#3129](https://github.com/ClickHouse/ClickHouse/pull/3129)
- The `Decimal` type now supports mathematical functions (`exp`, `sin` and so on.) [\#3129](https://github.com/ClickHouse/ClickHouse/pull/3129)
- The `system.part_log` table now has the `partition_id` column. [\#3089](https://github.com/ClickHouse/ClickHouse/pull/3089)
- The `Decimal` type now supports `var*` and `stddev*` aggregate functions. [#3129](https://github.com/ClickHouse/ClickHouse/pull/3129)
- The `Decimal` type now supports mathematical functions (`exp`, `sin` and so on.) [#3129](https://github.com/ClickHouse/ClickHouse/pull/3129)
- The `system.part_log` table now has the `partition_id` column. [#3089](https://github.com/ClickHouse/ClickHouse/pull/3089)
#### Bug Fixes: {#bug-fixes-11}
- `Merge` now works correctly on `Distributed` tables. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3159)
- Fixed incompatibility (unnecessary dependency on the `glibc` version) that made it impossible to run ClickHouse on `Ubuntu Precise` and older versions. The incompatibility arose in version 18.12.13. [\#3130](https://github.com/ClickHouse/ClickHouse/pull/3130)
- Fixed incompatibility (unnecessary dependency on the `glibc` version) that made it impossible to run ClickHouse on `Ubuntu Precise` and older versions. The incompatibility arose in version 18.12.13. [#3130](https://github.com/ClickHouse/ClickHouse/pull/3130)
- Fixed errors in the `enable_optimize_predicate_expression` setting. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3107)
- Fixed a minor issue with backwards compatibility that appeared when working with a cluster of replicas on versions earlier than 18.12.13 and simultaneously creating a new replica of a table on a server with a newer version (shown in the message `Can not clone replica, because the ... updated to new ClickHouse version`, which is logical, but shouldn’t happen). [\#3122](https://github.com/ClickHouse/ClickHouse/pull/3122)
- Fixed a minor issue with backwards compatibility that appeared when working with a cluster of replicas on versions earlier than 18.12.13 and simultaneously creating a new replica of a table on a server with a newer version (shown in the message `Can not clone replica, because the ... updated to new ClickHouse version`, which is logical, but shouldn’t happen). [#3122](https://github.com/ClickHouse/ClickHouse/pull/3122)
#### Backward Incompatible Changes: {#backward-incompatible-changes-2}
@ -326,19 +326,19 @@ toc_title: '2018'
#### New Features: {#new-features-3}
- Added support for `ALTER UPDATE` queries. [\#3035](https://github.com/ClickHouse/ClickHouse/pull/3035)
- Added the `allow_ddl` option, which restricts the user’s access to DDL queries. [\#3104](https://github.com/ClickHouse/ClickHouse/pull/3104)
- Added the `min_merge_bytes_to_use_direct_io` option for `MergeTree` engines, which allows you to set a threshold for the total size of the merge (when above the threshold, data part files will be handled using O\_DIRECT). [\#3117](https://github.com/ClickHouse/ClickHouse/pull/3117)
- The `system.merges` system table now contains the `partition_id` column. [\#3099](https://github.com/ClickHouse/ClickHouse/pull/3099)
- Added support for `ALTER UPDATE` queries. [#3035](https://github.com/ClickHouse/ClickHouse/pull/3035)
- Added the `allow_ddl` option, which restricts the user’s access to DDL queries. [#3104](https://github.com/ClickHouse/ClickHouse/pull/3104)
- Added the `min_merge_bytes_to_use_direct_io` option for `MergeTree` engines, which allows you to set a threshold for the total size of the merge (when above the threshold, data part files will be handled using O_DIRECT). [#3117](https://github.com/ClickHouse/ClickHouse/pull/3117)
- The `system.merges` system table now contains the `partition_id` column. [#3099](https://github.com/ClickHouse/ClickHouse/pull/3099)
#### Improvements {#improvements-3}
- If a data part remains unchanged during mutation, it isn’t downloaded by replicas. [\#3103](https://github.com/ClickHouse/ClickHouse/pull/3103)
- Autocomplete is available for names of settings when working with `clickhouse-client`. [\#3106](https://github.com/ClickHouse/ClickHouse/pull/3106)
- If a data part remains unchanged during mutation, it isn’t downloaded by replicas. [#3103](https://github.com/ClickHouse/ClickHouse/pull/3103)
- Autocomplete is available for names of settings when working with `clickhouse-client`. [#3106](https://github.com/ClickHouse/ClickHouse/pull/3106)
#### Bug Fixes: {#bug-fixes-12}
- Added a check for the sizes of arrays that are elements of `Nested` type fields when inserting. [\#3118](https://github.com/ClickHouse/ClickHouse/pull/3118)
- Added a check for the sizes of arrays that are elements of `Nested` type fields when inserting. [#3118](https://github.com/ClickHouse/ClickHouse/pull/3118)
- Fixed an error updating external dictionaries with the `ODBC` source and `hashed` storage. This error occurred in version 18.12.13.
- Fixed a crash when creating a temporary table from a query with an `IN` condition. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3098)
- Fixed an error in aggregate functions for arrays that can have `NULL` elements. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/3097)
@ -347,90 +347,90 @@ toc_title: '2018'
#### New Features: {#new-features-4}
- Added the `DECIMAL(digits, scale)` data type (`Decimal32(scale)`, `Decimal64(scale)`, `Decimal128(scale)`). To enable it, use the setting `allow_experimental_decimal_type`. [\#2846](https://github.com/ClickHouse/ClickHouse/pull/2846) [\#2970](https://github.com/ClickHouse/ClickHouse/pull/2970) [\#3008](https://github.com/ClickHouse/ClickHouse/pull/3008) [\#3047](https://github.com/ClickHouse/ClickHouse/pull/3047)
- New `WITH ROLLUP` modifier for `GROUP BY` (alternative syntax: `GROUP BY ROLLUP(...)`). [\#2948](https://github.com/ClickHouse/ClickHouse/pull/2948)
- Added the `DECIMAL(digits, scale)` data type (`Decimal32(scale)`, `Decimal64(scale)`, `Decimal128(scale)`). To enable it, use the setting `allow_experimental_decimal_type`. [#2846](https://github.com/ClickHouse/ClickHouse/pull/2846) [#2970](https://github.com/ClickHouse/ClickHouse/pull/2970) [#3008](https://github.com/ClickHouse/ClickHouse/pull/3008) [#3047](https://github.com/ClickHouse/ClickHouse/pull/3047)
- New `WITH ROLLUP` modifier for `GROUP BY` (alternative syntax: `GROUP BY ROLLUP(...)`). [#2948](https://github.com/ClickHouse/ClickHouse/pull/2948)
- In queries with JOIN, the star character expands to a list of columns in all tables, in compliance with the SQL standard. You can restore the old behavior by setting `asterisk_left_columns_only` to 1 on the user configuration level. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2787)
- Added support for JOIN with table functions. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2907)
- Autocomplete by pressing Tab in clickhouse-client. [Sergey Shcherbin](https://github.com/ClickHouse/ClickHouse/pull/2447)
- Ctrl+C in clickhouse-client clears a query that was entered. [\#2877](https://github.com/ClickHouse/ClickHouse/pull/2877)
- Added the `join_default_strictness` setting (values: `"`, `'any'`, `'all'`). This allows you to not specify `ANY` or `ALL` for `JOIN`. [\#2982](https://github.com/ClickHouse/ClickHouse/pull/2982)
- Each line of the server log related to query processing shows the query ID. [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Now you can get query execution logs in clickhouse-client (use the `send_logs_level` setting). With distributed query processing, logs are cascaded from all the servers. [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.query_log` and `system.processes` (`SHOW PROCESSLIST`) tables now have information about all changed settings when you run a query (the nested structure of the `Settings` data). Added the `log_query_settings` setting. [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.query_log` and `system.processes` tables now show information about the number of threads that are participating in query execution (see the `thread_numbers` column). [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added `ProfileEvents` counters that measure the time spent on reading and writing over the network and reading and writing to disk, the number of network errors, and the time spent waiting when network bandwidth is limited. [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added `ProfileEvents`counters that contain the system metrics from rusage (you can use them to get information about CPU usage in userspace and the kernel, page faults, and context switches), as well as taskstats metrics (use these to obtain information about I/O wait time, CPU wait time, and the amount of data read and recorded, both with and without page cache). [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `ProfileEvents` counters are applied globally and for each query, as well as for each query execution thread, which allows you to profile resource consumption by query in detail. [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added the `system.query_thread_log` table, which contains information about each query execution thread. Added the `log_query_threads` setting. [\#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.metrics` and `system.events` tables now have built-in documentation. [\#3016](https://github.com/ClickHouse/ClickHouse/pull/3016)
- Ctrl+C in clickhouse-client clears a query that was entered. [#2877](https://github.com/ClickHouse/ClickHouse/pull/2877)
- Added the `join_default_strictness` setting (values: `"`, `'any'`, `'all'`). This allows you to not specify `ANY` or `ALL` for `JOIN`. [#2982](https://github.com/ClickHouse/ClickHouse/pull/2982)
- Each line of the server log related to query processing shows the query ID. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Now you can get query execution logs in clickhouse-client (use the `send_logs_level` setting). With distributed query processing, logs are cascaded from all the servers. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.query_log` and `system.processes` (`SHOW PROCESSLIST`) tables now have information about all changed settings when you run a query (the nested structure of the `Settings` data). Added the `log_query_settings` setting. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.query_log` and `system.processes` tables now show information about the number of threads that are participating in query execution (see the `thread_numbers` column). [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added `ProfileEvents` counters that measure the time spent on reading and writing over the network and reading and writing to disk, the number of network errors, and the time spent waiting when network bandwidth is limited. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added `ProfileEvents`counters that contain the system metrics from rusage (you can use them to get information about CPU usage in userspace and the kernel, page faults, and context switches), as well as taskstats metrics (use these to obtain information about I/O wait time, CPU wait time, and the amount of data read and recorded, both with and without page cache). [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `ProfileEvents` counters are applied globally and for each query, as well as for each query execution thread, which allows you to profile resource consumption by query in detail. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- Added the `system.query_thread_log` table, which contains information about each query execution thread. Added the `log_query_threads` setting. [#2482](https://github.com/ClickHouse/ClickHouse/pull/2482)
- The `system.metrics` and `system.events` tables now have built-in documentation. [#3016](https://github.com/ClickHouse/ClickHouse/pull/3016)
- Added the `arrayEnumerateDense` function. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2975)
- Added the `arrayCumSumNonNegative` and `arrayDifference` functions. [Aleksey Studnev](https://github.com/ClickHouse/ClickHouse/pull/2942)
- Added the `retention` aggregate function. [Sundy Li](https://github.com/ClickHouse/ClickHouse/pull/2887)
- Now you can add (merge) states of aggregate functions by using the plus operator, and multiply the states of aggregate functions by a nonnegative constant. [\#3062](https://github.com/ClickHouse/ClickHouse/pull/3062) [\#3034](https://github.com/ClickHouse/ClickHouse/pull/3034)
- Tables in the MergeTree family now have the virtual column `_partition_id`. [\#3089](https://github.com/ClickHouse/ClickHouse/pull/3089)
- Now you can add (merge) states of aggregate functions by using the plus operator, and multiply the states of aggregate functions by a nonnegative constant. [#3062](https://github.com/ClickHouse/ClickHouse/pull/3062) [#3034](https://github.com/ClickHouse/ClickHouse/pull/3034)
- Tables in the MergeTree family now have the virtual column `_partition_id`. [#3089](https://github.com/ClickHouse/ClickHouse/pull/3089)
#### Experimental Features: {#experimental-features-1}
- Added the `LowCardinality(T)` data type. This data type automatically creates a local dictionary of values and allows data processing without unpacking the dictionary. [\#2830](https://github.com/ClickHouse/ClickHouse/pull/2830)
- Added a cache of JIT-compiled functions and a counter for the number of uses before compiling. To JIT compile expressions, enable the `compile_expressions` setting. [\#2990](https://github.com/ClickHouse/ClickHouse/pull/2990) [\#3077](https://github.com/ClickHouse/ClickHouse/pull/3077)
- Added the `LowCardinality(T)` data type. This data type automatically creates a local dictionary of values and allows data processing without unpacking the dictionary. [#2830](https://github.com/ClickHouse/ClickHouse/pull/2830)
- Added a cache of JIT-compiled functions and a counter for the number of uses before compiling. To JIT compile expressions, enable the `compile_expressions` setting. [#2990](https://github.com/ClickHouse/ClickHouse/pull/2990) [#3077](https://github.com/ClickHouse/ClickHouse/pull/3077)
#### Improvements: {#improvements-4}
- Fixed the problem with unlimited accumulation of the replication log when there are abandoned replicas. Added an effective recovery mode for replicas with a long lag.
- Improved performance of `GROUP BY` with multiple aggregation fields when one of them is string and the others are fixed length.
- Improved performance when using `PREWHERE` and with implicit transfer of expressions in `PREWHERE`.
- Improved parsing performance for text formats (`CSV`, `TSV`). [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2977) [\#2980](https://github.com/ClickHouse/ClickHouse/pull/2980)
- Improved parsing performance for text formats (`CSV`, `TSV`). [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2977) [#2980](https://github.com/ClickHouse/ClickHouse/pull/2980)
- Improved performance of reading strings and arrays in binary formats. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2955)
- Increased performance and reduced memory consumption for queries to `system.tables` and `system.columns` when there is a very large number of tables on a single server. [\#2953](https://github.com/ClickHouse/ClickHouse/pull/2953)
- Fixed a performance problem in the case of a large stream of queries that result in an error (the `_dl_addr` function is visible in `perf top`, but the server isn’t using much CPU). [\#2938](https://github.com/ClickHouse/ClickHouse/pull/2938)
- Increased performance and reduced memory consumption for queries to `system.tables` and `system.columns` when there is a very large number of tables on a single server. [#2953](https://github.com/ClickHouse/ClickHouse/pull/2953)
- Fixed a performance problem in the case of a large stream of queries that result in an error (the `_dl_addr` function is visible in `perf top`, but the server isn’t using much CPU). [#2938](https://github.com/ClickHouse/ClickHouse/pull/2938)
- Conditions are cast into the View (when `enable_optimize_predicate_expression` is enabled). [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2907)
- Improvements to the functionality for the `UUID` data type. [\#3074](https://github.com/ClickHouse/ClickHouse/pull/3074) [\#2985](https://github.com/ClickHouse/ClickHouse/pull/2985)
- The `UUID` data type is supported in The-Alchemist dictionaries. [\#2822](https://github.com/ClickHouse/ClickHouse/pull/2822)
- Improvements to the functionality for the `UUID` data type. [#3074](https://github.com/ClickHouse/ClickHouse/pull/3074) [#2985](https://github.com/ClickHouse/ClickHouse/pull/2985)
- The `UUID` data type is supported in The-Alchemist dictionaries. [#2822](https://github.com/ClickHouse/ClickHouse/pull/2822)
- The `visitParamExtractRaw` function works correctly with nested structures. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2974)
- When the `input_format_skip_unknown_fields` setting is enabled, object fields in `JSONEachRow` format are skipped correctly. [BlahGeek](https://github.com/ClickHouse/ClickHouse/pull/2958)
- For a `CASE` expression with conditions, you can now omit `ELSE`, which is equivalent to `ELSE NULL`. [\#2920](https://github.com/ClickHouse/ClickHouse/pull/2920)
- For a `CASE` expression with conditions, you can now omit `ELSE`, which is equivalent to `ELSE NULL`. [#2920](https://github.com/ClickHouse/ClickHouse/pull/2920)
- The operation timeout can now be configured when working with ZooKeeper. [urykhy](https://github.com/ClickHouse/ClickHouse/pull/2971)
- You can specify an offset for `LIMIT n, m` as `LIMIT n OFFSET m`. [\#2840](https://github.com/ClickHouse/ClickHouse/pull/2840)
- You can use the `SELECT TOP n` syntax as an alternative for `LIMIT`. [\#2840](https://github.com/ClickHouse/ClickHouse/pull/2840)
- You can specify an offset for `LIMIT n, m` as `LIMIT n OFFSET m`. [#2840](https://github.com/ClickHouse/ClickHouse/pull/2840)
- You can use the `SELECT TOP n` syntax as an alternative for `LIMIT`. [#2840](https://github.com/ClickHouse/ClickHouse/pull/2840)
- Increased the size of the queue to write to system tables, so the `SystemLog parameter queue is full` error doesn’t happen as often.
- The `windowFunnel` aggregate function now supports events that meet multiple conditions. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2801)
- Duplicate columns can be used in a `USING` clause for `JOIN`. [\#3006](https://github.com/ClickHouse/ClickHouse/pull/3006)
- `Pretty` formats now have a limit on column alignment by width. Use the `output_format_pretty_max_column_pad_width` setting. If a value is wider, it will still be displayed in its entirety, but the other cells in the table will not be too wide. [\#3003](https://github.com/ClickHouse/ClickHouse/pull/3003)
- Duplicate columns can be used in a `USING` clause for `JOIN`. [#3006](https://github.com/ClickHouse/ClickHouse/pull/3006)
- `Pretty` formats now have a limit on column alignment by width. Use the `output_format_pretty_max_column_pad_width` setting. If a value is wider, it will still be displayed in its entirety, but the other cells in the table will not be too wide. [#3003](https://github.com/ClickHouse/ClickHouse/pull/3003)
- The `odbc` table function now allows you to specify the database/schema name. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2885)
- Added the ability to use a username specified in the `clickhouse-client` config file. [Vladimir Kozbin](https://github.com/ClickHouse/ClickHouse/pull/2909)
- The `ZooKeeperExceptions` counter has been split into three counters: `ZooKeeperUserExceptions`, `ZooKeeperHardwareExceptions`, and `ZooKeeperOtherExceptions`.
- `ALTER DELETE` queries work for materialized views.
- Added randomization when running the cleanup thread periodically for `ReplicatedMergeTree` tables in order to avoid periodic load spikes when there are a very large number of `ReplicatedMergeTree` tables.
- Support for `ATTACH TABLE ... ON CLUSTER` queries. [\#3025](https://github.com/ClickHouse/ClickHouse/pull/3025)
- Support for `ATTACH TABLE ... ON CLUSTER` queries. [#3025](https://github.com/ClickHouse/ClickHouse/pull/3025)
#### Bug Fixes: {#bug-fixes-13}
- Fixed an issue with `Dictionary` tables (throws the `Size of offsets doesn't match size of column` or `Unknown compression method` exception). This bug appeared in version 18.10.3. [\#2913](https://github.com/ClickHouse/ClickHouse/issues/2913)
- Fixed a bug when merging `CollapsingMergeTree` tables if one of the data parts is empty (these parts are formed during merge or `ALTER DELETE` if all data was deleted), and the `vertical` algorithm was used for the merge. [\#3049](https://github.com/ClickHouse/ClickHouse/pull/3049)
- Fixed a race condition during `DROP` or `TRUNCATE` for `Memory` tables with a simultaneous `SELECT`, which could lead to server crashes. This bug appeared in version 1.1.54388. [\#3038](https://github.com/ClickHouse/ClickHouse/pull/3038)
- Fixed the possibility of data loss when inserting in `Replicated` tables if the `Session is expired` error is returned (data loss can be detected by the `ReplicatedDataLoss` metric). This error occurred in version 1.1.54378. [\#2939](https://github.com/ClickHouse/ClickHouse/pull/2939) [\#2949](https://github.com/ClickHouse/ClickHouse/pull/2949) [\#2964](https://github.com/ClickHouse/ClickHouse/pull/2964)
- Fixed a segfault during `JOIN ... ON`. [\#3000](https://github.com/ClickHouse/ClickHouse/pull/3000)
- Fixed the error searching column names when the `WHERE` expression consists entirely of a qualified column name, such as `WHERE table.column`. [\#2994](https://github.com/ClickHouse/ClickHouse/pull/2994)
- Fixed the “Not found column” error that occurred when executing distributed queries if a single column consisting of an IN expression with a subquery is requested from a remote server. [\#3087](https://github.com/ClickHouse/ClickHouse/pull/3087)
- Fixed the `Block structure mismatch in UNION stream: different number of columns` error that occurred for distributed queries if one of the shards is local and the other is not, and optimization of the move to `PREWHERE` is triggered. [\#2226](https://github.com/ClickHouse/ClickHouse/pull/2226) [\#3037](https://github.com/ClickHouse/ClickHouse/pull/3037) [\#3055](https://github.com/ClickHouse/ClickHouse/pull/3055) [\#3065](https://github.com/ClickHouse/ClickHouse/pull/3065) [\#3073](https://github.com/ClickHouse/ClickHouse/pull/3073) [\#3090](https://github.com/ClickHouse/ClickHouse/pull/3090) [\#3093](https://github.com/ClickHouse/ClickHouse/pull/3093)
- Fixed the `pointInPolygon` function for certain cases of non-convex polygons. [\#2910](https://github.com/ClickHouse/ClickHouse/pull/2910)
- Fixed the incorrect result when comparing `nan` with integers. [\#3024](https://github.com/ClickHouse/ClickHouse/pull/3024)
- Fixed an error in the `zlib-ng` library that could lead to segfault in rare cases. [\#2854](https://github.com/ClickHouse/ClickHouse/pull/2854)
- Fixed a memory leak when inserting into a table with `AggregateFunction` columns, if the state of the aggregate function is not simple (allocates memory separately), and if a single insertion request results in multiple small blocks. [\#3084](https://github.com/ClickHouse/ClickHouse/pull/3084)
- Fixed an issue with `Dictionary` tables (throws the `Size of offsets doesn't match size of column` or `Unknown compression method` exception). This bug appeared in version 18.10.3. [#2913](https://github.com/ClickHouse/ClickHouse/issues/2913)
- Fixed a bug when merging `CollapsingMergeTree` tables if one of the data parts is empty (these parts are formed during merge or `ALTER DELETE` if all data was deleted), and the `vertical` algorithm was used for the merge. [#3049](https://github.com/ClickHouse/ClickHouse/pull/3049)
- Fixed a race condition during `DROP` or `TRUNCATE` for `Memory` tables with a simultaneous `SELECT`, which could lead to server crashes. This bug appeared in version 1.1.54388. [#3038](https://github.com/ClickHouse/ClickHouse/pull/3038)
- Fixed the possibility of data loss when inserting in `Replicated` tables if the `Session is expired` error is returned (data loss can be detected by the `ReplicatedDataLoss` metric). This error occurred in version 1.1.54378. [#2939](https://github.com/ClickHouse/ClickHouse/pull/2939) [#2949](https://github.com/ClickHouse/ClickHouse/pull/2949) [#2964](https://github.com/ClickHouse/ClickHouse/pull/2964)
- Fixed a segfault during `JOIN ... ON`. [#3000](https://github.com/ClickHouse/ClickHouse/pull/3000)
- Fixed the error searching column names when the `WHERE` expression consists entirely of a qualified column name, such as `WHERE table.column`. [#2994](https://github.com/ClickHouse/ClickHouse/pull/2994)
- Fixed the “Not found column” error that occurred when executing distributed queries if a single column consisting of an IN expression with a subquery is requested from a remote server. [#3087](https://github.com/ClickHouse/ClickHouse/pull/3087)
- Fixed the `Block structure mismatch in UNION stream: different number of columns` error that occurred for distributed queries if one of the shards is local and the other is not, and optimization of the move to `PREWHERE` is triggered. [#2226](https://github.com/ClickHouse/ClickHouse/pull/2226) [#3037](https://github.com/ClickHouse/ClickHouse/pull/3037) [#3055](https://github.com/ClickHouse/ClickHouse/pull/3055) [#3065](https://github.com/ClickHouse/ClickHouse/pull/3065) [#3073](https://github.com/ClickHouse/ClickHouse/pull/3073) [#3090](https://github.com/ClickHouse/ClickHouse/pull/3090) [#3093](https://github.com/ClickHouse/ClickHouse/pull/3093)
- Fixed the `pointInPolygon` function for certain cases of non-convex polygons. [#2910](https://github.com/ClickHouse/ClickHouse/pull/2910)
- Fixed the incorrect result when comparing `nan` with integers. [#3024](https://github.com/ClickHouse/ClickHouse/pull/3024)
- Fixed an error in the `zlib-ng` library that could lead to segfault in rare cases. [#2854](https://github.com/ClickHouse/ClickHouse/pull/2854)
- Fixed a memory leak when inserting into a table with `AggregateFunction` columns, if the state of the aggregate function is not simple (allocates memory separately), and if a single insertion request results in multiple small blocks. [#3084](https://github.com/ClickHouse/ClickHouse/pull/3084)
- Fixed a race condition when creating and deleting the same `Buffer` or `MergeTree` table simultaneously.
- Fixed the possibility of a segfault when comparing tuples made up of certain non-trivial types, such as tuples. [\#2989](https://github.com/ClickHouse/ClickHouse/pull/2989)
- Fixed the possibility of a segfault when comparing tuples made up of certain non-trivial types, such as tuples. [#2989](https://github.com/ClickHouse/ClickHouse/pull/2989)
- Fixed the possibility of a segfault when running certain `ON CLUSTER` queries. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2960)
- Fixed an error in the `arrayDistinct` function for `Nullable` array elements. [\#2845](https://github.com/ClickHouse/ClickHouse/pull/2845) [\#2937](https://github.com/ClickHouse/ClickHouse/pull/2937)
- Fixed an error in the `arrayDistinct` function for `Nullable` array elements. [#2845](https://github.com/ClickHouse/ClickHouse/pull/2845) [#2937](https://github.com/ClickHouse/ClickHouse/pull/2937)
- The `enable_optimize_predicate_expression` option now correctly supports cases with `SELECT *`. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2929)
- Fixed the segfault when re-initializing the ZooKeeper session. [\#2917](https://github.com/ClickHouse/ClickHouse/pull/2917)
- Fixed the segfault when re-initializing the ZooKeeper session. [#2917](https://github.com/ClickHouse/ClickHouse/pull/2917)
- Fixed potential blocking when working with ZooKeeper.
- Fixed incorrect code for adding nested data structures in a `SummingMergeTree`.
- When allocating memory for states of aggregate functions, alignment is correctly taken into account, which makes it possible to use operations that require alignment when implementing states of aggregate functions. [chenxing-xc](https://github.com/ClickHouse/ClickHouse/pull/2808)
#### Security Fix: {#security-fix}
- Safe use of ODBC data sources. Interaction with ODBC drivers uses a separate `clickhouse-odbc-bridge` process. Errors in third-party ODBC drivers no longer cause problems with server stability or vulnerabilities. [\#2828](https://github.com/ClickHouse/ClickHouse/pull/2828) [\#2879](https://github.com/ClickHouse/ClickHouse/pull/2879) [\#2886](https://github.com/ClickHouse/ClickHouse/pull/2886) [\#2893](https://github.com/ClickHouse/ClickHouse/pull/2893) [\#2921](https://github.com/ClickHouse/ClickHouse/pull/2921)
- Fixed incorrect validation of the file path in the `catBoostPool` table function. [\#2894](https://github.com/ClickHouse/ClickHouse/pull/2894)
- Safe use of ODBC data sources. Interaction with ODBC drivers uses a separate `clickhouse-odbc-bridge` process. Errors in third-party ODBC drivers no longer cause problems with server stability or vulnerabilities. [#2828](https://github.com/ClickHouse/ClickHouse/pull/2828) [#2879](https://github.com/ClickHouse/ClickHouse/pull/2879) [#2886](https://github.com/ClickHouse/ClickHouse/pull/2886) [#2893](https://github.com/ClickHouse/ClickHouse/pull/2893) [#2921](https://github.com/ClickHouse/ClickHouse/pull/2921)
- Fixed incorrect validation of the file path in the `catBoostPool` table function. [#2894](https://github.com/ClickHouse/ClickHouse/pull/2894)
- The contents of system tables (`tables`, `databases`, `parts`, `columns`, `parts_columns`, `merges`, `mutations`, `replicas`, and `replication_queue`) are filtered according to the user’s configured access to databases (`allow_databases`). [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2856)
#### Backward Incompatible Changes: {#backward-incompatible-changes-3}
@ -442,9 +442,9 @@ toc_title: '2018'
- Most integration tests can now be run by commit.
- Code style checks can also be run by commit.
- The `memcpy` implementation is chosen correctly when building on CentOS7/Fedora. [Etienne Champetier](https://github.com/ClickHouse/ClickHouse/pull/2912)
- When using clang to build, some warnings from `-Weverything` have been added, in addition to the regular `-Wall-Wextra -Werror`. [\#2957](https://github.com/ClickHouse/ClickHouse/pull/2957)
- When using clang to build, some warnings from `-Weverything` have been added, in addition to the regular `-Wall-Wextra -Werror`. [#2957](https://github.com/ClickHouse/ClickHouse/pull/2957)
- Debugging the build uses the `jemalloc` debug option.
- The interface of the library for interacting with ZooKeeper is declared abstract. [\#2950](https://github.com/ClickHouse/ClickHouse/pull/2950)
- The interface of the library for interacting with ZooKeeper is declared abstract. [#2950](https://github.com/ClickHouse/ClickHouse/pull/2950)
## ClickHouse Release 18.10 {#clickhouse-release-18-10}
@ -452,37 +452,37 @@ toc_title: '2018'
#### New Features: {#new-features-5}
- HTTPS can be used for replication. [\#2760](https://github.com/ClickHouse/ClickHouse/pull/2760)
- Added the functions `murmurHash2_64`, `murmurHash3_32`, `murmurHash3_64`, and `murmurHash3_128` in addition to the existing `murmurHash2_32`. [\#2791](https://github.com/ClickHouse/ClickHouse/pull/2791)
- Support for Nullable types in the ClickHouse ODBC driver (`ODBCDriver2` output format). [\#2834](https://github.com/ClickHouse/ClickHouse/pull/2834)
- HTTPS can be used for replication. [#2760](https://github.com/ClickHouse/ClickHouse/pull/2760)
- Added the functions `murmurHash2_64`, `murmurHash3_32`, `murmurHash3_64`, and `murmurHash3_128` in addition to the existing `murmurHash2_32`. [#2791](https://github.com/ClickHouse/ClickHouse/pull/2791)
- Support for Nullable types in the ClickHouse ODBC driver (`ODBCDriver2` output format). [#2834](https://github.com/ClickHouse/ClickHouse/pull/2834)
- Support for `UUID` in the key columns.
#### Improvements: {#improvements-5}
- Clusters can be removed without restarting the server when they are deleted from the config files. [\#2777](https://github.com/ClickHouse/ClickHouse/pull/2777)
- External dictionaries can be removed without restarting the server when they are removed from config files. [\#2779](https://github.com/ClickHouse/ClickHouse/pull/2779)
- Clusters can be removed without restarting the server when they are deleted from the config files. [#2777](https://github.com/ClickHouse/ClickHouse/pull/2777)
- External dictionaries can be removed without restarting the server when they are removed from config files. [#2779](https://github.com/ClickHouse/ClickHouse/pull/2779)
- Added `SETTINGS` support for the `Kafka` table engine. [Alexander Marshalov](https://github.com/ClickHouse/ClickHouse/pull/2781)
- Improvements for the `UUID` data type (not yet complete). [\#2618](https://github.com/ClickHouse/ClickHouse/pull/2618)
- Support for empty parts after merges in the `SummingMergeTree`, `CollapsingMergeTree` and `VersionedCollapsingMergeTree` engines. [\#2815](https://github.com/ClickHouse/ClickHouse/pull/2815)
- Old records of completed mutations are deleted (`ALTER DELETE`). [\#2784](https://github.com/ClickHouse/ClickHouse/pull/2784)
- Improvements for the `UUID` data type (not yet complete). [#2618](https://github.com/ClickHouse/ClickHouse/pull/2618)
- Support for empty parts after merges in the `SummingMergeTree`, `CollapsingMergeTree` and `VersionedCollapsingMergeTree` engines. [#2815](https://github.com/ClickHouse/ClickHouse/pull/2815)
- Old records of completed mutations are deleted (`ALTER DELETE`). [#2784](https://github.com/ClickHouse/ClickHouse/pull/2784)
- Added the `system.merge_tree_settings` table. [Kirill Shvakov](https://github.com/ClickHouse/ClickHouse/pull/2841)
- The `system.tables` table now has dependency columns: `dependencies_database` and `dependencies_table`. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2851)
- Added the `max_partition_size_to_drop` config option. [\#2782](https://github.com/ClickHouse/ClickHouse/pull/2782)
- Added the `max_partition_size_to_drop` config option. [#2782](https://github.com/ClickHouse/ClickHouse/pull/2782)
- Added the `output_format_json_escape_forward_slashes` option. [Alexander Bocharov](https://github.com/ClickHouse/ClickHouse/pull/2812)
- Added the `max_fetch_partition_retries_count` setting. [\#2831](https://github.com/ClickHouse/ClickHouse/pull/2831)
- Added the `prefer_localhost_replica` setting for disabling the preference for a local replica and going to a local replica without inter-process interaction. [\#2832](https://github.com/ClickHouse/ClickHouse/pull/2832)
- Added the `max_fetch_partition_retries_count` setting. [#2831](https://github.com/ClickHouse/ClickHouse/pull/2831)
- Added the `prefer_localhost_replica` setting for disabling the preference for a local replica and going to a local replica without inter-process interaction. [#2832](https://github.com/ClickHouse/ClickHouse/pull/2832)
- The `quantileExact` aggregate function returns `nan` in the case of aggregation on an empty `Float32` or `Float64` set. [Sundy Li](https://github.com/ClickHouse/ClickHouse/pull/2855)
#### Bug Fixes: {#bug-fixes-14}
- Removed unnecessary escaping of the connection string parameters for ODBC, which made it impossible to establish a connection. This error occurred in version 18.6.0.
- Fixed the logic for processing `REPLACE PARTITION` commands in the replication queue. If there are two `REPLACE` commands for the same partition, the incorrect logic could cause one of them to remain in the replication queue and not be executed. [\#2814](https://github.com/ClickHouse/ClickHouse/pull/2814)
- Fixed a merge bug when all data parts were empty (parts that were formed from a merge or from `ALTER DELETE` if all data was deleted). This bug appeared in version 18.1.0. [\#2930](https://github.com/ClickHouse/ClickHouse/pull/2930)
- Fixed the logic for processing `REPLACE PARTITION` commands in the replication queue. If there are two `REPLACE` commands for the same partition, the incorrect logic could cause one of them to remain in the replication queue and not be executed. [#2814](https://github.com/ClickHouse/ClickHouse/pull/2814)
- Fixed a merge bug when all data parts were empty (parts that were formed from a merge or from `ALTER DELETE` if all data was deleted). This bug appeared in version 18.1.0. [#2930](https://github.com/ClickHouse/ClickHouse/pull/2930)
- Fixed an error for concurrent `Set` or `Join`. [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2823)
- Fixed the `Block structure mismatch in UNION stream: different number of columns` error that occurred for `UNION ALL` queries inside a sub-query if one of the `SELECT` queries contains duplicate column names. [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2094)
- Fixed a memory leak if an exception occurred when connecting to a MySQL server.
- Fixed incorrect clickhouse-client response code in case of a query error.
- Fixed incorrect behavior of materialized views containing DISTINCT. [\#2795](https://github.com/ClickHouse/ClickHouse/issues/2795)
- Fixed incorrect behavior of materialized views containing DISTINCT. [#2795](https://github.com/ClickHouse/ClickHouse/issues/2795)
#### Backward Incompatible Changes {#backward-incompatible-changes-4}
@ -490,10 +490,10 @@ toc_title: '2018'
#### Build Changes: {#build-changes-3}
- The allocator has been replaced: `jemalloc` is now used instead of `tcmalloc`. In some scenarios, this increases speed up to 20%. However, there are queries that have slowed by up to 20%. Memory consumption has been reduced by approximately 10% in some scenarios, with improved stability. With highly competitive loads, CPU usage in userspace and in system shows just a slight increase. [\#2773](https://github.com/ClickHouse/ClickHouse/pull/2773)
- Use of libressl from a submodule. [\#1983](https://github.com/ClickHouse/ClickHouse/pull/1983) [\#2807](https://github.com/ClickHouse/ClickHouse/pull/2807)
- Use of unixodbc from a submodule. [\#2789](https://github.com/ClickHouse/ClickHouse/pull/2789)
- Use of mariadb-connector-c from a submodule. [\#2785](https://github.com/ClickHouse/ClickHouse/pull/2785)
- The allocator has been replaced: `jemalloc` is now used instead of `tcmalloc`. In some scenarios, this increases speed up to 20%. However, there are queries that have slowed by up to 20%. Memory consumption has been reduced by approximately 10% in some scenarios, with improved stability. With highly competitive loads, CPU usage in userspace and in system shows just a slight increase. [#2773](https://github.com/ClickHouse/ClickHouse/pull/2773)
- Use of libressl from a submodule. [#1983](https://github.com/ClickHouse/ClickHouse/pull/1983) [#2807](https://github.com/ClickHouse/ClickHouse/pull/2807)
- Use of unixodbc from a submodule. [#2789](https://github.com/ClickHouse/ClickHouse/pull/2789)
- Use of mariadb-connector-c from a submodule. [#2785](https://github.com/ClickHouse/ClickHouse/pull/2785)
- Added functional test files to the repository that depend on the availability of test data (for the time being, without the test data itself).
## ClickHouse Release 18.6 {#clickhouse-release-18-6}
@ -504,12 +504,12 @@ toc_title: '2018'
- Added support for ON expressions for the JOIN ON syntax:
`JOIN ON Expr([table.]column ...) = Expr([table.]column, ...) [AND Expr([table.]column, ...) = Expr([table.]column, ...) ...]`
The expression must be a chain of equalities joined by the AND operator. Each side of the equality can be an arbitrary expression over the columns of one of the tables. The use of fully qualified column names is supported (`table.name`, `database.table.name`, `table_alias.name`, `subquery_alias.name`) for the right table. [\#2742](https://github.com/ClickHouse/ClickHouse/pull/2742)
- HTTPS can be enabled for replication. [\#2760](https://github.com/ClickHouse/ClickHouse/pull/2760)
The expression must be a chain of equalities joined by the AND operator. Each side of the equality can be an arbitrary expression over the columns of one of the tables. The use of fully qualified column names is supported (`table.name`, `database.table.name`, `table_alias.name`, `subquery_alias.name`) for the right table. [#2742](https://github.com/ClickHouse/ClickHouse/pull/2742)
- HTTPS can be enabled for replication. [#2760](https://github.com/ClickHouse/ClickHouse/pull/2760)
#### Improvements: {#improvements-6}
- The server passes the patch component of its version to the client. Data about the patch version component is in `system.processes` and `query_log`. [\#2646](https://github.com/ClickHouse/ClickHouse/pull/2646)
- The server passes the patch component of its version to the client. Data about the patch version component is in `system.processes` and `query_log`. [#2646](https://github.com/ClickHouse/ClickHouse/pull/2646)
## ClickHouse Release 18.5 {#clickhouse-release-18-5}
@ -517,16 +517,16 @@ toc_title: '2018'
#### New Features: {#new-features-7}
- Added the hash function `murmurHash2_32` [\#2756](https://github.com/ClickHouse/ClickHouse/pull/2756).
- Added the hash function `murmurHash2_32` [#2756](https://github.com/ClickHouse/ClickHouse/pull/2756).
#### Improvements: {#improvements-7}
- Now you can use the `from_env` [\#2741](https://github.com/ClickHouse/ClickHouse/pull/2741) attribute to set values in config files from environment variables.
- Added case-insensitive versions of the `coalesce`, `ifNull`, and `nullIf functions` [\#2752](https://github.com/ClickHouse/ClickHouse/pull/2752).
- Now you can use the `from_env` [#2741](https://github.com/ClickHouse/ClickHouse/pull/2741) attribute to set values in config files from environment variables.
- Added case-insensitive versions of the `coalesce`, `ifNull`, and `nullIf functions` [#2752](https://github.com/ClickHouse/ClickHouse/pull/2752).
#### Bug Fixes: {#bug-fixes-15}
- Fixed a possible bug when starting a replica [\#2759](https://github.com/ClickHouse/ClickHouse/pull/2759).
- Fixed a possible bug when starting a replica [#2759](https://github.com/ClickHouse/ClickHouse/pull/2759).
## ClickHouse Release 18.4 {#clickhouse-release-18-4}
@ -534,15 +534,15 @@ toc_title: '2018'
#### New Features: {#new-features-8}
- Added system tables: `formats`, `data_type_families`, `aggregate_function_combinators`, `table_functions`, `table_engines`, `collations` [\#2721](https://github.com/ClickHouse/ClickHouse/pull/2721).
- Added the ability to use a table function instead of a table as an argument of a `remote` or `cluster table function` [\#2708](https://github.com/ClickHouse/ClickHouse/pull/2708).
- Support for `HTTP Basic` authentication in the replication protocol [\#2727](https://github.com/ClickHouse/ClickHouse/pull/2727).
- Added system tables: `formats`, `data_type_families`, `aggregate_function_combinators`, `table_functions`, `table_engines`, `collations` [#2721](https://github.com/ClickHouse/ClickHouse/pull/2721).
- Added the ability to use a table function instead of a table as an argument of a `remote` or `cluster table function` [#2708](https://github.com/ClickHouse/ClickHouse/pull/2708).
- Support for `HTTP Basic` authentication in the replication protocol [#2727](https://github.com/ClickHouse/ClickHouse/pull/2727).
- The `has` function now allows searching for a numeric value in an array of `Enum` values [Maxim Khrisanfov](https://github.com/ClickHouse/ClickHouse/pull/2699).
- Support for adding arbitrary message separators when reading from `Kafka` [Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2701).
#### Improvements: {#improvements-8}
- The `ALTER TABLE t DELETE WHERE` query does not rewrite data parts that were not affected by the WHERE condition [\#2694](https://github.com/ClickHouse/ClickHouse/pull/2694).
- The `ALTER TABLE t DELETE WHERE` query does not rewrite data parts that were not affected by the WHERE condition [#2694](https://github.com/ClickHouse/ClickHouse/pull/2694).
- The `use_minimalistic_checksums_in_zookeeper` option for `ReplicatedMergeTree` tables is enabled by default. This setting was added in version 1.1.54378, 2018-04-16. Versions that are older than 1.1.54378 can no longer be installed.
- Support for running `KILL` and `OPTIMIZE` queries that specify `ON CLUSTER` [Winter Zhang](https://github.com/ClickHouse/ClickHouse/pull/2689).
@ -563,11 +563,11 @@ toc_title: '2018'
#### New Features: {#new-features-9}
- Support for the `ALTER TABLE t DELETE WHERE` query for non-replicated MergeTree tables ([\#2634](https://github.com/ClickHouse/ClickHouse/pull/2634)).
- Support for arbitrary types for the `uniq*` family of aggregate functions ([\#2010](https://github.com/ClickHouse/ClickHouse/issues/2010)).
- Support for arbitrary types in comparison operators ([\#2026](https://github.com/ClickHouse/ClickHouse/issues/2026)).
- The `users.xml` file allows setting a subnet mask in the format `10.0.0.1/255.255.255.0`. This is necessary for using masks for IPv6 networks with zeros in the middle ([\#2637](https://github.com/ClickHouse/ClickHouse/pull/2637)).
- Added the `arrayDistinct` function ([\#2670](https://github.com/ClickHouse/ClickHouse/pull/2670)).
- Support for the `ALTER TABLE t DELETE WHERE` query for non-replicated MergeTree tables ([#2634](https://github.com/ClickHouse/ClickHouse/pull/2634)).
- Support for arbitrary types for the `uniq*` family of aggregate functions ([#2010](https://github.com/ClickHouse/ClickHouse/issues/2010)).
- Support for arbitrary types in comparison operators ([#2026](https://github.com/ClickHouse/ClickHouse/issues/2026)).
- The `users.xml` file allows setting a subnet mask in the format `10.0.0.1/255.255.255.0`. This is necessary for using masks for IPv6 networks with zeros in the middle ([#2637](https://github.com/ClickHouse/ClickHouse/pull/2637)).
- Added the `arrayDistinct` function ([#2670](https://github.com/ClickHouse/ClickHouse/pull/2670)).
- The SummingMergeTree engine can now work with AggregateFunction type columns ([Constantin S. Pan](https://github.com/ClickHouse/ClickHouse/pull/2566)).
#### Improvements: {#improvements-9}
@ -580,12 +580,12 @@ toc_title: '2018'
- Fixed the TRUNCATE command for temporary tables ([Amos Bird](https://github.com/ClickHouse/ClickHouse/pull/2624)).
- Fixed a rare deadlock in the ZooKeeper client library that occurred when there was a network error while reading the response ([c315200](https://github.com/ClickHouse/ClickHouse/commit/c315200e64b87e44bdf740707fc857d1fdf7e947)).
- Fixed an error during a CAST to Nullable types ([\#1322](https://github.com/ClickHouse/ClickHouse/issues/1322)).
- Fixed an error during a CAST to Nullable types ([#1322](https://github.com/ClickHouse/ClickHouse/issues/1322)).
- Fixed the incorrect result of the `maxIntersection()` function when the boundaries of intervals coincided ([Michael Furmur](https://github.com/ClickHouse/ClickHouse/pull/2657)).
- Fixed incorrect transformation of the OR expression chain in a function argument ([chenxing-xc](https://github.com/ClickHouse/ClickHouse/pull/2663)).
- Fixed performance degradation for queries containing `IN (subquery)` expressions inside another subquery ([\#2571](https://github.com/ClickHouse/ClickHouse/issues/2571)).
- Fixed performance degradation for queries containing `IN (subquery)` expressions inside another subquery ([#2571](https://github.com/ClickHouse/ClickHouse/issues/2571)).
- Fixed incompatibility between servers with different versions in distributed queries that use a `CAST` function that isn’t in uppercase letters ([fe8c4d6](https://github.com/ClickHouse/ClickHouse/commit/fe8c4d64e434cacd4ceef34faa9005129f2190a5)).
- Added missing quoting of identifiers for queries to an external DBMS ([\#2635](https://github.com/ClickHouse/ClickHouse/issues/2635)).
- Added missing quoting of identifiers for queries to an external DBMS ([#2635](https://github.com/ClickHouse/ClickHouse/issues/2635)).
#### Backward Incompatible Changes: {#backward-incompatible-changes-6}
@ -604,9 +604,9 @@ toc_title: '2018'
- Fixed a problem with a very small timeout for sockets (one second) for reading and writing when sending and downloading replicated data, which made it impossible to download larger parts if there is a load on the network or disk (it resulted in cyclical attempts to download parts). This error occurred in version 1.1.54388.
- Fixed issues when using chroot in ZooKeeper if you inserted duplicate data blocks in the table.
- The `has` function now works correctly for an array with Nullable elements ([\#2115](https://github.com/ClickHouse/ClickHouse/issues/2115)).
- The `has` function now works correctly for an array with Nullable elements ([#2115](https://github.com/ClickHouse/ClickHouse/issues/2115)).
- The `system.tables` table now works correctly when used in distributed queries. The `metadata_modification_time` and `engine_full` columns are now non-virtual. Fixed an error that occurred if only these columns were queried from the table.
- Fixed how an empty `TinyLog` table works after inserting an empty data block ([\#2563](https://github.com/ClickHouse/ClickHouse/issues/2563)).
- Fixed how an empty `TinyLog` table works after inserting an empty data block ([#2563](https://github.com/ClickHouse/ClickHouse/issues/2563)).
- The `system.zookeeper` table works if the value of the node in ZooKeeper is NULL.
### ClickHouse Release 1.1.54390, 2018-07-06 {#clickhouse-release-1-1-54390-2018-07-06}
@ -619,12 +619,12 @@ toc_title: '2018'
#### Improvements: {#improvements-10}
- Improved performance, reduced memory consumption, and correct memory consumption tracking with use of the IN operator when a table index could be used ([\#2584](https://github.com/ClickHouse/ClickHouse/pull/2584)).
- Improved performance, reduced memory consumption, and correct memory consumption tracking with use of the IN operator when a table index could be used ([#2584](https://github.com/ClickHouse/ClickHouse/pull/2584)).
- Removed redundant checking of checksums when adding a data part. This is important when there are a large number of replicas, because in these cases the total number of checks was equal to N^2.
- Added support for `Array(Tuple(...))` arguments for the `arrayEnumerateUniq` function ([\#2573](https://github.com/ClickHouse/ClickHouse/pull/2573)).
- Added `Nullable` support for the `runningDifference` function ([\#2594](https://github.com/ClickHouse/ClickHouse/pull/2594)).
- Improved query analysis performance when there is a very large number of expressions ([\#2572](https://github.com/ClickHouse/ClickHouse/pull/2572)).
- Faster selection of data parts for merging in `ReplicatedMergeTree` tables. Faster recovery of the ZooKeeper session ([\#2597](https://github.com/ClickHouse/ClickHouse/pull/2597)).
- Added support for `Array(Tuple(...))` arguments for the `arrayEnumerateUniq` function ([#2573](https://github.com/ClickHouse/ClickHouse/pull/2573)).
- Added `Nullable` support for the `runningDifference` function ([#2594](https://github.com/ClickHouse/ClickHouse/pull/2594)).
- Improved query analysis performance when there is a very large number of expressions ([#2572](https://github.com/ClickHouse/ClickHouse/pull/2572)).
- Faster selection of data parts for merging in `ReplicatedMergeTree` tables. Faster recovery of the ZooKeeper session ([#2597](https://github.com/ClickHouse/ClickHouse/pull/2597)).
- The `format_version.txt` file for `MergeTree` tables is re-created if it is missing, which makes sense if ClickHouse is launched after copying the directory structure without files ([Ciprian Hacman](https://github.com/ClickHouse/ClickHouse/pull/2593)).
#### Bug Fixes: {#bug-fixes-19}
@ -632,9 +632,9 @@ toc_title: '2018'
- Fixed a bug when working with ZooKeeper that could make it impossible to recover the session and readonly states of tables before restarting the server.
- Fixed a bug when working with ZooKeeper that could result in old nodes not being deleted if the session is interrupted.
- Fixed an error in the `quantileTDigest` function for Float arguments (this bug was introduced in version 1.1.54388) ([Mikhail Surin](https://github.com/ClickHouse/ClickHouse/pull/2553)).
- Fixed a bug in the index for MergeTree tables if the primary key column is located inside the function for converting types between signed and unsigned integers of the same size ([\#2603](https://github.com/ClickHouse/ClickHouse/pull/2603)).
- Fixed segfault if `macros` are used but they aren’t in the config file ([\#2570](https://github.com/ClickHouse/ClickHouse/pull/2570)).
- Fixed switching to the default database when reconnecting the client ([\#2583](https://github.com/ClickHouse/ClickHouse/pull/2583)).
- Fixed a bug in the index for MergeTree tables if the primary key column is located inside the function for converting types between signed and unsigned integers of the same size ([#2603](https://github.com/ClickHouse/ClickHouse/pull/2603)).
- Fixed segfault if `macros` are used but they aren’t in the config file ([#2570](https://github.com/ClickHouse/ClickHouse/pull/2570)).
- Fixed switching to the default database when reconnecting the client ([#2583](https://github.com/ClickHouse/ClickHouse/pull/2583)).
- Fixed a bug that occurred when the `use_index_for_in_with_subqueries` setting was disabled.
#### Security Fix: {#security-fix-1}
@ -670,23 +670,23 @@ toc_title: '2018'
- Duplicates no longer appear for a query with `DISTINCT` and `ORDER BY`.
- Queries with `ARRAY JOIN` and `arrayFilter` no longer return an incorrect result.
- Fixed an error when reading an array column from a Nested structure ([\#2066](https://github.com/ClickHouse/ClickHouse/issues/2066)).
- Fixed an error when reading an array column from a Nested structure ([#2066](https://github.com/ClickHouse/ClickHouse/issues/2066)).
- Fixed an error when analyzing queries with a HAVING clause like `HAVING tuple IN (...)`.
- Fixed an error when analyzing queries with recursive aliases.
- Fixed an error when reading from ReplacingMergeTree with a condition in PREWHERE that filters all rows ([\#2525](https://github.com/ClickHouse/ClickHouse/issues/2525)).
- Fixed an error when reading from ReplacingMergeTree with a condition in PREWHERE that filters all rows ([#2525](https://github.com/ClickHouse/ClickHouse/issues/2525)).
- User profile settings were not applied when using sessions in the HTTP interface.
- Fixed how settings are applied from the command line parameters in clickhouse-local.
- The ZooKeeper client library now uses the session timeout received from the server.
- Fixed a bug in the ZooKeeper client library when the client waited for the server response longer than the timeout.
- Fixed pruning of parts for queries with conditions on partition key columns ([\#2342](https://github.com/ClickHouse/ClickHouse/issues/2342)).
- Merges are now possible after `CLEAR COLUMN IN PARTITION` ([\#2315](https://github.com/ClickHouse/ClickHouse/issues/2315)).
- Fixed pruning of parts for queries with conditions on partition key columns ([#2342](https://github.com/ClickHouse/ClickHouse/issues/2342)).
- Merges are now possible after `CLEAR COLUMN IN PARTITION` ([#2315](https://github.com/ClickHouse/ClickHouse/issues/2315)).
- Type mapping in the ODBC table function has been fixed ([sundy-li](https://github.com/ClickHouse/ClickHouse/pull/2268)).
- Type comparisons have been fixed for `DateTime` with and without the time zone ([Alexander Bocharov](https://github.com/ClickHouse/ClickHouse/pull/2400)).
- Fixed syntactic parsing and formatting of the `CAST` operator.
- Fixed insertion into a materialized view for the Distributed table engine ([Babacar Diassé](https://github.com/ClickHouse/ClickHouse/pull/2411)).
- Fixed a race condition when writing data from the `Kafka` engine to materialized views ([Yangkuan Liu](https://github.com/ClickHouse/ClickHouse/pull/2448)).
- Fixed SSRF in the remote() table function.
- Fixed exit behavior of `clickhouse-client` in multiline mode ([\#2510](https://github.com/ClickHouse/ClickHouse/issues/2510)).
- Fixed exit behavior of `clickhouse-client` in multiline mode ([#2510](https://github.com/ClickHouse/ClickHouse/issues/2510)).
#### Improvements: {#improvements-11}
@ -710,7 +710,7 @@ toc_title: '2018'
- Fixed the build using the vectorclass library ([Babacar Diassé](https://github.com/ClickHouse/ClickHouse/pull/2274)).
- Cmake now generates files for ninja by default (like when using `-G Ninja`).
- Added the ability to use the libtinfo library instead of libtermcap ([Georgy Kondratiev](https://github.com/ClickHouse/ClickHouse/pull/2519)).
- Fixed a header file conflict in Fedora Rawhide ([\#2520](https://github.com/ClickHouse/ClickHouse/issues/2520)).
- Fixed a header file conflict in Fedora Rawhide ([#2520](https://github.com/ClickHouse/ClickHouse/issues/2520)).
#### Backward Incompatible Changes: {#backward-incompatible-changes-7}
@ -793,10 +793,10 @@ toc_title: '2018'
- The `max_execution_time` limit now works correctly with distributed queries.
- Fixed errors when calculating the size of composite columns in the `system.columns` table.
- Fixed an error when creating a temporary table `CREATE TEMPORARY TABLE IF NOT EXISTS.`
- Fixed errors in `StorageKafka` (\#\#2075)
- Fixed errors in `StorageKafka` (##2075)
- Fixed server crashes from invalid arguments of certain aggregate functions.
- Fixed the error that prevented the `DETACH DATABASE` query from stopping background tasks for `ReplicatedMergeTree` tables.
- `Too many parts` state is less likely to happen when inserting into aggregated materialized views (\#\#2084).
- `Too many parts` state is less likely to happen when inserting into aggregated materialized views (##2084).
- Corrected recursive handling of substitutions in the config if a substitution must be followed by another substitution on the same level.
- Corrected the syntax in the metadata file when creating a `VIEW` that uses a query with `UNION ALL`.
- `SummingMergeTree` now works correctly for summation of nested data structures with a composite key.

2536
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@ -51,7 +51,7 @@ Credits: Andrey Krasichkov and Evgeny Sidorov of Yandex Information Security Tea
### CVE-2018-14668 {#cve-2018-14668}
“remote” table function allowed arbitrary symbols in “user”, “password” and “default\_database” fields which led to Cross Protocol Request Forgery Attacks.
“remote” table function allowed arbitrary symbols in “user”, “password” and “default_database” fields which led to Cross Protocol Request Forgery Attacks.
Credits: Andrey Krasichkov of Yandex Information Security Team

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docs/es/development/architecture.md
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@ -47,7 +47,7 @@ A `Block` es un contenedor que representa un subconjunto (porción) de una tabla
Cuando calculamos alguna función sobre columnas en un bloque, agregamos otra columna con su resultado al bloque, y no tocamos columnas para argumentos de la función porque las operaciones son inmutables. Más tarde, las columnas innecesarias se pueden eliminar del bloque, pero no se pueden modificar. Es conveniente para la eliminación de subexpresiones comunes.
Se crean bloques para cada fragmento de datos procesado. Tenga en cuenta que para el mismo tipo de cálculo, los nombres y tipos de columna siguen siendo los mismos para diferentes bloques y solo cambian los datos de columna. Es mejor dividir los datos del bloque desde el encabezado del bloque porque los tamaños de bloque pequeños tienen una gran sobrecarga de cadenas temporales para copiar shared\_ptrs y nombres de columna.
Se crean bloques para cada fragmento de datos procesado. Tenga en cuenta que para el mismo tipo de cálculo, los nombres y tipos de columna siguen siendo los mismos para diferentes bloques y solo cambian los datos de columna. Es mejor dividir los datos del bloque desde el encabezado del bloque porque los tamaños de bloque pequeños tienen una gran sobrecarga de cadenas temporales para copiar shared_ptrs y nombres de columna.
## Bloquear flujos {#block-streams}

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