ClickHouse/CHANGELOG.md

## ClickHouse release 21.4

### ClickHouse release 21.4.1 2021-04-08

#### Backward Incompatible Change

* The `toStartOfIntervalFunction` will align hour intervals to the midnight (in previous versions they were aligned to the start of unix epoch). For example, `toStartOfInterval(x, INTERVAL 11 HOUR)` will split every day into three intervals: `00:00:00..10:59:59`, `11:00:00..21:59:59` and `22:00:00..23:59:59`. This behaviour is more suited for practical needs. This closes [#9510](https://github.com/ClickHouse/ClickHouse/issues/9510). [#22060](https://github.com/ClickHouse/ClickHouse/pull/22060) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* `Age` and `Precision` in graphite rollup configs should increase from retention to retention. Now it's checked and the wrong config raises an exception. [#21496](https://github.com/ClickHouse/ClickHouse/pull/21496) ([Mikhail f. Shiryaev](https://github.com/Felixoid)).
* Fix `cutToFirstSignificantSubdomainCustom()`/`firstSignificantSubdomainCustom()` returning wrong result for 3+ level domains present in custom top-level domain list. For input domains matching these custom top-level domains, the third-level domain was considered to be the first significant one. This is now fixed. This change may introduce incompatibility if the function is used in e.g. the sharding key. [#21946](https://github.com/ClickHouse/ClickHouse/pull/21946) ([Azat Khuzhin](https://github.com/azat)).
* Column `keys` in table `system.dictionaries` was replaced to columns `key.names` and `key.types`. Columns `key.names`, `key.types`, `attribute.names`, `attribute.types` from `system.dictionaries` table does not require dictionary to be loaded. [#21884](https://github.com/ClickHouse/ClickHouse/pull/21884) ([Maksim Kita](https://github.com/kitaisreal)).
* Now replicas that are processing the `ALTER TABLE ATTACH PART[ITION]` command search in their `detached/` folders before fetching the data from other replicas. As an implementation detail, a new command `ATTACH_PART` is introduced in the replicated log. Parts are searched and compared by their checksums. [#18978](https://github.com/ClickHouse/ClickHouse/pull/18978) ([Mike Kot](https://github.com/myrrc)). **Note**:
  * `ATTACH PART[ITION]` queries may not work during cluster upgrade.
  * It's not possible to rollback to older ClickHouse version after executing `ALTER ... ATTACH` query in new version as the old servers would fail to pass the `ATTACH_PART` entry in the replicated log.

#### New Feature

* Extended range of `DateTime64` to support dates from year 1925 to 2283. Improved support of `DateTime` around zero date (`1970-01-01`). [#9404](https://github.com/ClickHouse/ClickHouse/pull/9404) ([alexey-milovidov](https://github.com/alexey-milovidov), [Vasily Nemkov](https://github.com/Enmk)).
* Add `prefer_column_name_to_alias` setting to use original column names instead of aliases. it is needed to be more compatible with common databases' aliasing rules. This is for [#9715](https://github.com/ClickHouse/ClickHouse/issues/9715) and [#9887](https://github.com/ClickHouse/ClickHouse/issues/9887). [#22044](https://github.com/ClickHouse/ClickHouse/pull/22044) ([Amos Bird](https://github.com/amosbird)).
* Added functions `dictGetChildren(dictionary, key)`, `dictGetDescendants(dictionary, key, level)`. Function `dictGetChildren` return all children as an array if indexes. It is a inverse transformation for `dictGetHierarchy`. Function `dictGetDescendants` return all descendants as if `dictGetChildren` was applied `level` times recursively. Zero `level` value is equivalent to infinity. Closes [#14656](https://github.com/ClickHouse/ClickHouse/issues/14656). [#22096](https://github.com/ClickHouse/ClickHouse/pull/22096) ([Maksim Kita](https://github.com/kitaisreal)).
* Added `executable_pool` dictionary source. Close [#14528](https://github.com/ClickHouse/ClickHouse/issues/14528). [#21321](https://github.com/ClickHouse/ClickHouse/pull/21321) ([Maksim Kita](https://github.com/kitaisreal)).
* Added table function `dictionary`. It works the same way as `Dictionary` engine. Closes [#21560](https://github.com/ClickHouse/ClickHouse/issues/21560). [#21910](https://github.com/ClickHouse/ClickHouse/pull/21910) ([Maksim Kita](https://github.com/kitaisreal)).
* Support `Nullable` type for `PolygonDictionary` attribute. [#21890](https://github.com/ClickHouse/ClickHouse/pull/21890) ([Maksim Kita](https://github.com/kitaisreal)).
* Functions `dictGet`, `dictHas` use current database name if it is not specified for dictionaries created with DDL. Closes [#21632](https://github.com/ClickHouse/ClickHouse/issues/21632). [#21859](https://github.com/ClickHouse/ClickHouse/pull/21859) ([Maksim Kita](https://github.com/kitaisreal)).
* Added function `dictGetOrNull`. It works like `dictGet`, but return `Null` in case key was not found in dictionary. Closes [#22375](https://github.com/ClickHouse/ClickHouse/issues/22375). [#22413](https://github.com/ClickHouse/ClickHouse/pull/22413) ([Maksim Kita](https://github.com/kitaisreal)).
* Added async update in `ComplexKeyCache`, `SSDCache`, `SSDComplexKeyCache` dictionaries. Added support for `Nullable` type in `Cache`, `ComplexKeyCache`, `SSDCache`, `SSDComplexKeyCache` dictionaries. Added support for multiple attributes fetch with `dictGet`, `dictGetOrDefault` functions. Fixes [#21517](https://github.com/ClickHouse/ClickHouse/issues/21517). [#20595](https://github.com/ClickHouse/ClickHouse/pull/20595) ([Maksim Kita](https://github.com/kitaisreal)).
* Support `dictHas` function for `RangeHashedDictionary`. Fixes [#6680](https://github.com/ClickHouse/ClickHouse/issues/6680). [#19816](https://github.com/ClickHouse/ClickHouse/pull/19816) ([Maksim Kita](https://github.com/kitaisreal)).
* Add function `timezoneOf` that returns the timezone name of `DateTime` or `DateTime64` data types. This does not close [#9959](https://github.com/ClickHouse/ClickHouse/issues/9959). Fix inconsistencies in function names: add aliases `timezone` and `timeZone` as well as `toTimezone` and `toTimeZone` and `timezoneOf` and `timeZoneOf`. [#22001](https://github.com/ClickHouse/ClickHouse/pull/22001) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add new optional clause `GRANTEES` for `CREATE/ALTER USER` commands. It specifies users or roles which are allowed to receive grants from this user on condition this user has also all required access granted with grant option. By default `GRANTEES ANY` is used which means a user with grant option can grant to anyone. Syntax: `CREATE USER ... GRANTEES {user | role | ANY | NONE} [,...] [EXCEPT {user | role} [,...]]`. [#21641](https://github.com/ClickHouse/ClickHouse/pull/21641) ([Vitaly Baranov](https://github.com/vitlibar)).
* Add new column `slowdowns_count` to `system.clusters`. When using hedged requests, it shows how many times we switched to another replica because this replica was responding slowly. Also show actual value of `errors_count` in `system.clusters`. [#21480](https://github.com/ClickHouse/ClickHouse/pull/21480) ([Kruglov Pavel](https://github.com/Avogar)).
* Add `_partition_id` virtual column for `MergeTree*` engines. Allow to prune partitions by `_partition_id`. Add `partitionID()` function to calculate partition id string. [#21401](https://github.com/ClickHouse/ClickHouse/pull/21401) ([Amos Bird](https://github.com/amosbird)).
* Add function `isIPAddressInRange` to test if an IPv4 or IPv6 address is contained in a given CIDR network prefix. [#21329](https://github.com/ClickHouse/ClickHouse/pull/21329) ([PHO](https://github.com/depressed-pho)).
* Added new SQL command `ALTER TABLE 'table_name' UNFREEZE [PARTITION 'part_expr'] WITH NAME 'backup_name'`. This command is needed to properly remove 'freezed' partitions from all disks. [#21142](https://github.com/ClickHouse/ClickHouse/pull/21142) ([Pavel Kovalenko](https://github.com/Jokser)).
* Supports implicit key type conversion for JOIN. [#19885](https://github.com/ClickHouse/ClickHouse/pull/19885) ([Vladimir](https://github.com/vdimir)).

#### Experimental Feature

* Support `RANGE OFFSET` frame (for window functions) for floating point types. Implement `lagInFrame`/`leadInFrame` window functions, which are analogous to `lag`/`lead`, but respect the window frame. They are identical when the frame is `between unbounded preceding and unbounded following`. This closes [#5485](https://github.com/ClickHouse/ClickHouse/issues/5485). [#21895](https://github.com/ClickHouse/ClickHouse/pull/21895) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Zero-copy replication for `ReplicatedMergeTree` over S3 storage. [#16240](https://github.com/ClickHouse/ClickHouse/pull/16240) ([ianton-ru](https://github.com/ianton-ru)).
* Added possibility to migrate existing S3 disk to the schema with backup-restore capabilities. [#22070](https://github.com/ClickHouse/ClickHouse/pull/22070) ([Pavel Kovalenko](https://github.com/Jokser)).

#### Performance Improvement

* Supported parallel formatting in `clickhouse-local` and everywhere else. [#21630](https://github.com/ClickHouse/ClickHouse/pull/21630) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Support parallel parsing for `CSVWithNames` and `TSVWithNames` formats. This closes [#21085](https://github.com/ClickHouse/ClickHouse/issues/21085). [#21149](https://github.com/ClickHouse/ClickHouse/pull/21149) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Enable read with mmap IO for file ranges from 64 MiB (the settings `min_bytes_to_use_mmap_io`). It may lead to moderate performance improvement. [#22326](https://github.com/ClickHouse/ClickHouse/pull/22326) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add cache for files read with `min_bytes_to_use_mmap_io` setting. It makes significant (2x and more) performance improvement when the value of the setting is small by avoiding frequent mmap/munmap calls and the consequent page faults. Note that mmap IO has major drawbacks that makes it less reliable in production (e.g. hung or SIGBUS on faulty disks; less controllable memory usage). Nevertheless it is good in benchmarks. [#22206](https://github.com/ClickHouse/ClickHouse/pull/22206) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Avoid unnecessary data copy when using codec `NONE`. Please note that codec `NONE` is mostly useless - it's recommended to always use compression (`LZ4` is by default). Despite the common belief, disabling compression may not improve performance (the opposite effect is possible). The `NONE` codec is useful in some cases: - when data is uncompressable; - for synthetic benchmarks. [#22145](https://github.com/ClickHouse/ClickHouse/pull/22145) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Faster `GROUP BY` with small `max_rows_to_group_by` and `group_by_overflow_mode='any'`. [#21856](https://github.com/ClickHouse/ClickHouse/pull/21856) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Optimize performance of queries like `SELECT ... FINAL ... WHERE`. Now in queries with `FINAL` it's allowed to move to `PREWHERE` columns, which are in sorting key. [#21830](https://github.com/ClickHouse/ClickHouse/pull/21830) ([foolchi](https://github.com/foolchi)).
* Improved performance by replacing `memcpy` to another implementation. This closes [#18583](https://github.com/ClickHouse/ClickHouse/issues/18583). [#21520](https://github.com/ClickHouse/ClickHouse/pull/21520) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Improve performance of aggregation in order of sorting key (with enabled setting `optimize_aggregation_in_order`). [#19401](https://github.com/ClickHouse/ClickHouse/pull/19401) ([Anton Popov](https://github.com/CurtizJ)).

#### Improvement

* Add connection pool for PostgreSQL table/database engine and dictionary source. Should fix [#21444](https://github.com/ClickHouse/ClickHouse/issues/21444). [#21839](https://github.com/ClickHouse/ClickHouse/pull/21839) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Support non-default table schema for postgres storage/table-function. Closes [#21701](https://github.com/ClickHouse/ClickHouse/issues/21701). [#21711](https://github.com/ClickHouse/ClickHouse/pull/21711) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Support replicas priority for postgres dictionary source. [#21710](https://github.com/ClickHouse/ClickHouse/pull/21710) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Introduce a new merge tree setting `min_bytes_to_rebalance_partition_over_jbod` which allows assigning new parts to different disks of a JBOD volume in a balanced way. [#16481](https://github.com/ClickHouse/ClickHouse/pull/16481) ([Amos Bird](https://github.com/amosbird)).
* Added `Grant`, `Revoke` and `System` values of `query_kind` column for corresponding queries in `system.query_log`. [#21102](https://github.com/ClickHouse/ClickHouse/pull/21102) ([Vasily Nemkov](https://github.com/Enmk)).
* Allow customizing timeouts for HTTP connections used for replication independently from other HTTP timeouts. [#20088](https://github.com/ClickHouse/ClickHouse/pull/20088) ([nvartolomei](https://github.com/nvartolomei)).
* Better exception message in client in case of exception while server is writing blocks. In previous versions client may get misleading message like `Data compressed with different methods`. [#22427](https://github.com/ClickHouse/ClickHouse/pull/22427) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix error `Directory tmp_fetch_XXX already exists` which could happen after failed fetch part. Delete temporary fetch directory if it already exists. Fixes [#14197](https://github.com/ClickHouse/ClickHouse/issues/14197). [#22411](https://github.com/ClickHouse/ClickHouse/pull/22411) ([nvartolomei](https://github.com/nvartolomei)).
* Fix MSan report for function `range` with `UInt256` argument (support for large integers is experimental). This closes [#22157](https://github.com/ClickHouse/ClickHouse/issues/22157). [#22387](https://github.com/ClickHouse/ClickHouse/pull/22387) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add `current_database` column to `system.processes` table. It contains the current database of the query. [#22365](https://github.com/ClickHouse/ClickHouse/pull/22365) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Add case-insensitive history search/navigation and subword movement features to `clickhouse-client`. [#22105](https://github.com/ClickHouse/ClickHouse/pull/22105) ([Amos Bird](https://github.com/amosbird)).
* If tuple of NULLs, e.g. `(NULL, NULL)` is on the left hand side of `IN` operator with tuples of non-NULLs on the right hand side, e.g. `SELECT (NULL, NULL) IN ((0, 0), (3, 1))` return 0 instead of throwing an exception about incompatible types. The expression may also appear due to optimization of something like `SELECT (NULL, NULL) = (8, 0) OR (NULL, NULL) = (3, 2) OR (NULL, NULL) = (0, 0) OR (NULL, NULL) = (3, 1)`. This closes [#22017](https://github.com/ClickHouse/ClickHouse/issues/22017). [#22063](https://github.com/ClickHouse/ClickHouse/pull/22063) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Update used version of simdjson to 0.9.1. This fixes [#21984](https://github.com/ClickHouse/ClickHouse/issues/21984). [#22057](https://github.com/ClickHouse/ClickHouse/pull/22057) ([Vitaly Baranov](https://github.com/vitlibar)).
* Added case insensitive aliases for `CONNECTION_ID()` and `VERSION()` functions. This fixes [#22028](https://github.com/ClickHouse/ClickHouse/issues/22028). [#22042](https://github.com/ClickHouse/ClickHouse/pull/22042) ([Eugene Klimov](https://github.com/Slach)).
* Add option `strict_increase` to `windowFunnel` function to calculate each event once (resolve [#21835](https://github.com/ClickHouse/ClickHouse/issues/21835)). [#22025](https://github.com/ClickHouse/ClickHouse/pull/22025) ([Vladimir](https://github.com/vdimir)).
* If partition key of a `MergeTree` table does not include `Date` or `DateTime` columns but includes exactly one `DateTime64` column, expose its values in the `min_time` and `max_time` columns in `system.parts` and `system.parts_columns` tables. Add `min_time` and `max_time` columns to `system.parts_columns` table (these was inconsistency to the `system.parts` table). This closes [#18244](https://github.com/ClickHouse/ClickHouse/issues/18244). [#22011](https://github.com/ClickHouse/ClickHouse/pull/22011) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Supported `replication_alter_partitions_sync=1` setting in `clickhouse-copier` for moving partitions from helping table to destination. Decreased default timeouts. Fixes [#21911](https://github.com/ClickHouse/ClickHouse/issues/21911). [#21912](https://github.com/ClickHouse/ClickHouse/pull/21912) ([turbo jason](https://github.com/songenjie)).
* Show path to data directory of `EmbeddedRocksDB` tables in system tables. [#21903](https://github.com/ClickHouse/ClickHouse/pull/21903) ([tavplubix](https://github.com/tavplubix)).
* Add profile event `HedgedRequestsChangeReplica`, change read data timeout from sec to ms. [#21886](https://github.com/ClickHouse/ClickHouse/pull/21886) ([Kruglov Pavel](https://github.com/Avogar)).
* DiskS3 (experimental feature under development). Fixed bug with the impossibility to move directory if the destination is not empty and cache disk is used. [#21837](https://github.com/ClickHouse/ClickHouse/pull/21837) ([Pavel Kovalenko](https://github.com/Jokser)).
* Better formatting for `Array` and `Map` data types in Web UI. [#21798](https://github.com/ClickHouse/ClickHouse/pull/21798) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Update clusters only if their configurations were updated. [#21685](https://github.com/ClickHouse/ClickHouse/pull/21685) ([Kruglov Pavel](https://github.com/Avogar)).
* Propagate query and session settings for distributed DDL queries. Set `distributed_ddl_entry_format_version` to 2 to enable this. Added `distributed_ddl_output_mode` setting. Supported modes: `none`, `throw` (default), `null_status_on_timeout` and `never_throw`. Miscellaneous fixes and improvements for `Replicated` database engine. [#21535](https://github.com/ClickHouse/ClickHouse/pull/21535) ([tavplubix](https://github.com/tavplubix)).
* If `PODArray` was instantiated with element size that is neither a fraction or a multiple of 16, buffer overflow was possible. No bugs in current releases exist. [#21533](https://github.com/ClickHouse/ClickHouse/pull/21533) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add `last_error_time`/`last_error_message`/`last_error_stacktrace`/`remote` columns for `system.errors`. [#21529](https://github.com/ClickHouse/ClickHouse/pull/21529) ([Azat Khuzhin](https://github.com/azat)).
* Add aliases `simpleJSONExtract/simpleJSONHas` to `visitParam/visitParamExtract{UInt, Int, Bool, Float, Raw, String}`. Fixes #21383. [#21519](https://github.com/ClickHouse/ClickHouse/pull/21519) ([fastio](https://github.com/fastio)).
* Add setting `optimize_skip_unused_shards_limit` to limit the number of sharding key values for `optimize_skip_unused_shards`. [#21512](https://github.com/ClickHouse/ClickHouse/pull/21512) ([Azat Khuzhin](https://github.com/azat)).
* Improve `clickhouse-format` to not throw exception when there are extra spaces or comment after the last query, and throw exception early with readable message when format `ASTInsertQuery` with data . [#21311](https://github.com/ClickHouse/ClickHouse/pull/21311) ([flynn](https://github.com/ucasFL)).
* Improve support of integer keys in data type `Map`. [#21157](https://github.com/ClickHouse/ClickHouse/pull/21157) ([Anton Popov](https://github.com/CurtizJ)).
* MaterializeMySQL: attempt to reconnect to MySQL if the connection is lost. [#20961](https://github.com/ClickHouse/ClickHouse/pull/20961) ([Håvard Kvålen](https://github.com/havardk)).
* Support more cases to rewrite `CROSS JOIN` to `INNER JOIN`. [#20392](https://github.com/ClickHouse/ClickHouse/pull/20392) ([Vladimir](https://github.com/vdimir)).
* Do not create empty parts on INSERT when `optimize_on_insert` setting enabled. Fixes [#20304](https://github.com/ClickHouse/ClickHouse/issues/20304). [#20387](https://github.com/ClickHouse/ClickHouse/pull/20387) ([Kruglov Pavel](https://github.com/Avogar)).
* `MaterializeMySQL`: add minmax skipping index for `_version` column. [#20382](https://github.com/ClickHouse/ClickHouse/pull/20382) ([Stig Bakken](https://github.com/stigsb)).
* Add option `--backslash` for `clickhouse-format`, which can add a backslash at the end of each line of the formatted query. [#21494](https://github.com/ClickHouse/ClickHouse/pull/21494) ([flynn](https://github.com/ucasFL)).
* Now clickhouse will not throw `LOGICAL_ERROR` exception when we try to mutate the already covered part. Fixes [#22013](https://github.com/ClickHouse/ClickHouse/issues/22013). [#22291](https://github.com/ClickHouse/ClickHouse/pull/22291) ([alesapin](https://github.com/alesapin)).

#### Bug Fix

* Remove socket from epoll before cancelling packet receiver in `HedgedConnections` to prevent possible race. Fixes [#22161](https://github.com/ClickHouse/ClickHouse/issues/22161). [#22443](https://github.com/ClickHouse/ClickHouse/pull/22443) ([Kruglov Pavel](https://github.com/Avogar)).
* Add (missing) memory accounting in parallel parsing routines. In previous versions OOM was possible when the resultset contains very large blocks of data. This closes [#22008](https://github.com/ClickHouse/ClickHouse/issues/22008). [#22425](https://github.com/ClickHouse/ClickHouse/pull/22425) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix exception which may happen when `SELECT` has constant `WHERE` condition and source table has columns which names are digits. [#22270](https://github.com/ClickHouse/ClickHouse/pull/22270) ([LiuNeng](https://github.com/liuneng1994)).
* Fix query cancellation with `use_hedged_requests=0` and `async_socket_for_remote=1`. [#22183](https://github.com/ClickHouse/ClickHouse/pull/22183) ([Azat Khuzhin](https://github.com/azat)).
* Fix uncaught exception in `InterserverIOHTTPHandler`. [#22146](https://github.com/ClickHouse/ClickHouse/pull/22146) ([Azat Khuzhin](https://github.com/azat)).
* Fix docker entrypoint in case `http_port` is not in the config. [#22132](https://github.com/ClickHouse/ClickHouse/pull/22132) ([Ewout](https://github.com/devwout)).
* Fix error `Invalid number of rows in Chunk` in `JOIN` with `TOTALS` and `arrayJoin`. Closes [#19303](https://github.com/ClickHouse/ClickHouse/issues/19303). [#22129](https://github.com/ClickHouse/ClickHouse/pull/22129) ([Vladimir](https://github.com/vdimir)).
* Fix the background thread pool name which used to poll message from Kafka. The Kafka engine with the broken thread pool will not consume the message from message queue. [#22122](https://github.com/ClickHouse/ClickHouse/pull/22122) ([fastio](https://github.com/fastio)).
* Fix waiting for `OPTIMIZE` and `ALTER` queries for `ReplicatedMergeTree` table engines. Now the query will not hang when the table was detached or restarted. [#22118](https://github.com/ClickHouse/ClickHouse/pull/22118) ([alesapin](https://github.com/alesapin)).
* Disable `async_socket_for_remote`/`use_hedged_requests` for buggy Linux kernels. [#22109](https://github.com/ClickHouse/ClickHouse/pull/22109) ([Azat Khuzhin](https://github.com/azat)).
* Docker entrypoint: avoid chown of `.` in case when `LOG_PATH` is empty. Closes [#22100](https://github.com/ClickHouse/ClickHouse/issues/22100). [#22102](https://github.com/ClickHouse/ClickHouse/pull/22102) ([filimonov](https://github.com/filimonov)).
* The function `decrypt` was lacking a check for the minimal size of data encrypted in `AEAD` mode. This closes [#21897](https://github.com/ClickHouse/ClickHouse/issues/21897). [#22064](https://github.com/ClickHouse/ClickHouse/pull/22064) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* In rare case, merge for `CollapsingMergeTree` may create granule with `index_granularity + 1` rows. Because of this, internal check, added in [#18928](https://github.com/ClickHouse/ClickHouse/issues/18928) (affects 21.2 and 21.3), may fail with error `Incomplete granules are not allowed while blocks are granules size`. This error did not allow parts to merge. [#21976](https://github.com/ClickHouse/ClickHouse/pull/21976) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Reverted [#15454](https://github.com/ClickHouse/ClickHouse/issues/15454) that may cause significant increase in memory usage while loading external dictionaries of hashed type. This closes [#21935](https://github.com/ClickHouse/ClickHouse/issues/21935). [#21948](https://github.com/ClickHouse/ClickHouse/pull/21948) ([Maksim Kita](https://github.com/kitaisreal)).
* Prevent hedged connections overlaps (`Unknown packet 9 from server` error). [#21941](https://github.com/ClickHouse/ClickHouse/pull/21941) ([Azat Khuzhin](https://github.com/azat)).
* Fix reading the HTTP POST request with "multipart/form-data" content type in some cases. [#21936](https://github.com/ClickHouse/ClickHouse/pull/21936) ([Ivan](https://github.com/abyss7)).
* Fix wrong `ORDER BY` results when a query contains window functions, and optimization for reading in primary key order is applied. Fixes [#21828](https://github.com/ClickHouse/ClickHouse/issues/21828). [#21915](https://github.com/ClickHouse/ClickHouse/pull/21915) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Fix deadlock in first catboost model execution. Closes [#13832](https://github.com/ClickHouse/ClickHouse/issues/13832). [#21844](https://github.com/ClickHouse/ClickHouse/pull/21844) ([Kruglov Pavel](https://github.com/Avogar)).
* Fix incorrect query result (and possible crash) which could happen when `WHERE` or `HAVING` condition is pushed before `GROUP BY`. Fixes [#21773](https://github.com/ClickHouse/ClickHouse/issues/21773). [#21841](https://github.com/ClickHouse/ClickHouse/pull/21841) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Better error handling and logging in `WriteBufferFromS3`. [#21836](https://github.com/ClickHouse/ClickHouse/pull/21836) ([Pavel Kovalenko](https://github.com/Jokser)).
* Fix possible crashes in aggregate functions with combinator `Distinct`, while using two-level aggregation. This is a follow-up fix of [#18365](https://github.com/ClickHouse/ClickHouse/pull/18365) . Can only reproduced in production env. [#21818](https://github.com/ClickHouse/ClickHouse/pull/21818) ([Amos Bird](https://github.com/amosbird)).
* Fix scalar subquery index analysis. This fixes [#21717](https://github.com/ClickHouse/ClickHouse/issues/21717) , which was introduced in [#18896](https://github.com/ClickHouse/ClickHouse/pull/18896). [#21766](https://github.com/ClickHouse/ClickHouse/pull/21766) ([Amos Bird](https://github.com/amosbird)).
* Fix bug for `ReplicatedMerge` table engines when `ALTER MODIFY COLUMN` query doesn't change the type of `Decimal` column if its size (32 bit or 64 bit) doesn't change. [#21728](https://github.com/ClickHouse/ClickHouse/pull/21728) ([alesapin](https://github.com/alesapin)).
* Fix possible infinite waiting when concurrent `OPTIMIZE` and `DROP` are run for `ReplicatedMergeTree`. [#21716](https://github.com/ClickHouse/ClickHouse/pull/21716) ([Azat Khuzhin](https://github.com/azat)).
* Fix function `arrayElement` with type `Map` for constant integer arguments. [#21699](https://github.com/ClickHouse/ClickHouse/pull/21699) ([Anton Popov](https://github.com/CurtizJ)).
* Fix SIGSEGV on not existing attributes from `ip_trie` with `access_to_key_from_attributes`. [#21692](https://github.com/ClickHouse/ClickHouse/pull/21692) ([Azat Khuzhin](https://github.com/azat)).
* Server now start accepting connections only after `DDLWorker` and dictionaries initialization. [#21676](https://github.com/ClickHouse/ClickHouse/pull/21676) ([Azat Khuzhin](https://github.com/azat)).
* Add type conversion for keys of tables of type `Join` (previously led to SIGSEGV). [#21646](https://github.com/ClickHouse/ClickHouse/pull/21646) ([Azat Khuzhin](https://github.com/azat)).
* Fix distributed requests cancellation (for example simple select from multiple shards with limit, i.e. `select * from remote('127.{2,3}', system.numbers) limit 100`) with `async_socket_for_remote=1`. [#21643](https://github.com/ClickHouse/ClickHouse/pull/21643) ([Azat Khuzhin](https://github.com/azat)).
* Fix `fsync_part_directory` for horizontal merge. [#21642](https://github.com/ClickHouse/ClickHouse/pull/21642) ([Azat Khuzhin](https://github.com/azat)).
* Remove unknown columns from joined table in `WHERE` for queries to external database engines (MySQL, PostgreSQL). close [#14614](https://github.com/ClickHouse/ClickHouse/issues/14614), close [#19288](https://github.com/ClickHouse/ClickHouse/issues/19288) (dup), close [#19645](https://github.com/ClickHouse/ClickHouse/issues/19645) (dup). [#21640](https://github.com/ClickHouse/ClickHouse/pull/21640) ([Vladimir](https://github.com/vdimir)).
* `std::terminate` was called if there is an error writing data into s3. [#21624](https://github.com/ClickHouse/ClickHouse/pull/21624) ([Vladimir](https://github.com/vdimir)).
* Fix possible error `Cannot find column` when `optimize_skip_unused_shards` is enabled and zero shards are used. [#21579](https://github.com/ClickHouse/ClickHouse/pull/21579) ([Azat Khuzhin](https://github.com/azat)).
* In case if query has constant `WHERE` condition, and setting `optimize_skip_unused_shards` enabled, all shards may be skipped and query could return incorrect empty result. [#21550](https://github.com/ClickHouse/ClickHouse/pull/21550) ([Amos Bird](https://github.com/amosbird)).
* Fix table function `clusterAllReplicas` returns wrong `_shard_num`. close [#21481](https://github.com/ClickHouse/ClickHouse/issues/21481). [#21498](https://github.com/ClickHouse/ClickHouse/pull/21498) ([flynn](https://github.com/ucasFL)).
* Fix that S3 table holds old credentials after config update. [#21457](https://github.com/ClickHouse/ClickHouse/pull/21457) ([Grigory Pervakov](https://github.com/GrigoryPervakov)).
* Fixed race on SSL object inside `SecureSocket` in Poco. [#21456](https://github.com/ClickHouse/ClickHouse/pull/21456) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Fix `Avro` format parsing for `Kafka`. Fixes [#21437](https://github.com/ClickHouse/ClickHouse/issues/21437). [#21438](https://github.com/ClickHouse/ClickHouse/pull/21438) ([Ilya Golshtein](https://github.com/ilejn)).
* Fix receive and send timeouts and non-blocking read in secure socket. [#21429](https://github.com/ClickHouse/ClickHouse/pull/21429) ([Kruglov Pavel](https://github.com/Avogar)).
* `force_drop_table` flag didn't work for `MATERIALIZED VIEW`, it's fixed. Fixes [#18943](https://github.com/ClickHouse/ClickHouse/issues/18943). [#20626](https://github.com/ClickHouse/ClickHouse/pull/20626) ([tavplubix](https://github.com/tavplubix)).
* Fix name clashes in `PredicateRewriteVisitor`. It caused incorrect `WHERE` filtration after full join. Close [#20497](https://github.com/ClickHouse/ClickHouse/issues/20497). [#20622](https://github.com/ClickHouse/ClickHouse/pull/20622) ([Vladimir](https://github.com/vdimir)).
* Fixed open behavior of remote host filter in case when there is `remote_url_allow_hosts` section in configuration but no entries there. [#20058](https://github.com/ClickHouse/ClickHouse/pull/20058) ([Vladimir Chebotarev](https://github.com/excitoon)).

#### Build/Testing/Packaging Improvement

* Add [Jepsen](https://github.com/jepsen-io/jepsen) tests for ClickHouse Keeper. [#21677](https://github.com/ClickHouse/ClickHouse/pull/21677) ([alesapin](https://github.com/alesapin)).
* Run stateless tests in parallel in CI. Depends on [#22181](https://github.com/ClickHouse/ClickHouse/issues/22181). [#22300](https://github.com/ClickHouse/ClickHouse/pull/22300) ([alesapin](https://github.com/alesapin)).
* Enable status check for [SQLancer](https://github.com/sqlancer/sqlancer) CI run. [#22015](https://github.com/ClickHouse/ClickHouse/pull/22015) ([Ilya Yatsishin](https://github.com/qoega)).
* Multiple preparations for PowerPC builds: Enable the bundled openldap on `ppc64le`. [#22487](https://github.com/ClickHouse/ClickHouse/pull/22487) ([Kfir Itzhak](https://github.com/mastertheknife)).  Enable compiling on `ppc64le` with Clang. [#22476](https://github.com/ClickHouse/ClickHouse/pull/22476) ([Kfir Itzhak](https://github.com/mastertheknife)). Fix compiling boost on `ppc64le`. [#22474](https://github.com/ClickHouse/ClickHouse/pull/22474) ([Kfir Itzhak](https://github.com/mastertheknife)). Fix CMake error about internal CMake variable `CMAKE_ASM_COMPILE_OBJECT` not set on `ppc64le`. [#22469](https://github.com/ClickHouse/ClickHouse/pull/22469) ([Kfir Itzhak](https://github.com/mastertheknife)). Fix Fedora/RHEL/CentOS not finding `libclang_rt.builtins` on `ppc64le`. [#22458](https://github.com/ClickHouse/ClickHouse/pull/22458) ([Kfir Itzhak](https://github.com/mastertheknife)).  Enable building with `jemalloc` on `ppc64le`. [#22447](https://github.com/ClickHouse/ClickHouse/pull/22447) ([Kfir Itzhak](https://github.com/mastertheknife)). Fix ClickHouse's config embedding and cctz's timezone embedding on `ppc64le`. [#22445](https://github.com/ClickHouse/ClickHouse/pull/22445) ([Kfir Itzhak](https://github.com/mastertheknife)). Fixed compiling on `ppc64le` and use the correct instruction pointer register on `ppc64le`. [#22430](https://github.com/ClickHouse/ClickHouse/pull/22430) ([Kfir Itzhak](https://github.com/mastertheknife)).
* Re-enable the S3 (AWS) library on `aarch64`. [#22484](https://github.com/ClickHouse/ClickHouse/pull/22484) ([Kfir Itzhak](https://github.com/mastertheknife)).
* Add `tzdata` to Docker containers because reading `ORC` formats requires it. This closes [#14156](https://github.com/ClickHouse/ClickHouse/issues/14156). [#22000](https://github.com/ClickHouse/ClickHouse/pull/22000) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Introduce 2 arguments for `clickhouse-server` image Dockerfile: `deb_location` & `single_binary_location`. [#21977](https://github.com/ClickHouse/ClickHouse/pull/21977) ([filimonov](https://github.com/filimonov)).
* Allow to use clang-tidy with release builds by enabling assertions if it is used. [#21914](https://github.com/ClickHouse/ClickHouse/pull/21914) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add llvm-12 binaries name to search in cmake scripts. Implicit constants conversions to mute clang warnings. Updated submodules to build with CMake 3.19. Mute recursion in macro expansion in `readpassphrase` library. Deprecated `-fuse-ld` changed to `--ld-path` for clang. [#21597](https://github.com/ClickHouse/ClickHouse/pull/21597) ([Ilya Yatsishin](https://github.com/qoega)).
* Updating `docker/test/testflows/runner/dockerd-entrypoint.sh` to use Yandex dockerhub-proxy, because Docker Hub has enabled very restrictive rate limits [#21551](https://github.com/ClickHouse/ClickHouse/pull/21551) ([vzakaznikov](https://github.com/vzakaznikov)).
* Fix macOS shared lib build. [#20184](https://github.com/ClickHouse/ClickHouse/pull/20184) ([nvartolomei](https://github.com/nvartolomei)).
* Add `ctime` option to `zookeeper-dump-tree`. It allows to dump node creation time. [#21842](https://github.com/ClickHouse/ClickHouse/pull/21842) ([Ilya](https://github.com/HumanUser)).


## ClickHouse release 21.3 (LTS)

### ClickHouse release v21.3, 2021-03-12

#### Backward Incompatible Change

* Now it's not allowed to create MergeTree tables in old syntax with table TTL because it's just ignored. Attach of old tables is still possible. [#20282](https://github.com/ClickHouse/ClickHouse/pull/20282) ([alesapin](https://github.com/alesapin)).
* Now all case-insensitive function names will be rewritten to their canonical representations. This is needed for projection query routing (the upcoming feature). [#20174](https://github.com/ClickHouse/ClickHouse/pull/20174) ([Amos Bird](https://github.com/amosbird)).
* Fix creation of `TTL` in cases, when its expression is a function and it is the same as `ORDER BY` key. Now it's allowed to set custom aggregation to primary key columns in `TTL` with `GROUP BY`. Backward incompatible: For primary key columns, which are not in `GROUP BY` and aren't set explicitly now is applied function `any` instead of `max`, when TTL is expired. Also if you use TTL with `WHERE` or `GROUP BY` you can see exceptions at merges, while making rolling update. [#15450](https://github.com/ClickHouse/ClickHouse/pull/15450) ([Anton Popov](https://github.com/CurtizJ)).

#### New Feature

* Add file engine settings: `engine_file_empty_if_not_exists` and `engine_file_truncate_on_insert`. [#20620](https://github.com/ClickHouse/ClickHouse/pull/20620) ([M0r64n](https://github.com/M0r64n)).
* Add aggregate function `deltaSum` for summing the differences between consecutive rows. [#20057](https://github.com/ClickHouse/ClickHouse/pull/20057) ([Russ Frank](https://github.com/rf)).
* New `event_time_microseconds` column in `system.part_log` table. [#20027](https://github.com/ClickHouse/ClickHouse/pull/20027) ([Bharat Nallan](https://github.com/bharatnc)).
* Added `timezoneOffset(datetime)` function which will give the offset from UTC in seconds. This close [#issue:19850](https://github.com/ClickHouse/ClickHouse/issues/19850). [#19962](https://github.com/ClickHouse/ClickHouse/pull/19962) ([keenwolf](https://github.com/keen-wolf)).
* Add setting `insert_shard_id` to support insert data into specific shard from distributed table. [#19961](https://github.com/ClickHouse/ClickHouse/pull/19961) ([flynn](https://github.com/ucasFL)).
* Function `reinterpretAs` updated to support big integers. Fixes [#19691](https://github.com/ClickHouse/ClickHouse/issues/19691). [#19858](https://github.com/ClickHouse/ClickHouse/pull/19858) ([Maksim Kita](https://github.com/kitaisreal)).
* Added Server Side Encryption Customer Keys (the `x-amz-server-side-encryption-customer-(key/md5)` header) support in S3 client. See [the link](https://docs.aws.amazon.com/AmazonS3/latest/dev/ServerSideEncryptionCustomerKeys.html). Closes [#19428](https://github.com/ClickHouse/ClickHouse/issues/19428). [#19748](https://github.com/ClickHouse/ClickHouse/pull/19748) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Added `implicit_key` option for `executable` dictionary source. It allows to avoid printing key for every record if records comes in the same order as the input keys. Implements [#14527](https://github.com/ClickHouse/ClickHouse/issues/14527). [#19677](https://github.com/ClickHouse/ClickHouse/pull/19677) ([Maksim Kita](https://github.com/kitaisreal)).
* Add quota type `query_selects` and `query_inserts`. [#19603](https://github.com/ClickHouse/ClickHouse/pull/19603) ([JackyWoo](https://github.com/JackyWoo)).
* Add function `extractTextFromHTML` [#19600](https://github.com/ClickHouse/ClickHouse/pull/19600) ([zlx19950903](https://github.com/zlx19950903)), ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Tables with `MergeTree*` engine now have two new table-level settings for query concurrency control. Setting `max_concurrent_queries` limits the number of concurrently executed queries which are related to this table. Setting `min_marks_to_honor_max_concurrent_queries` tells to apply previous setting only if query reads at least this number of marks. [#19544](https://github.com/ClickHouse/ClickHouse/pull/19544) ([Amos Bird](https://github.com/amosbird)).
* Added `file` function to read file from user_files directory as a String. This is different from the `file` table function. This implements [#issue:18851](https://github.com/ClickHouse/ClickHouse/issues/18851). [#19204](https://github.com/ClickHouse/ClickHouse/pull/19204) ([keenwolf](https://github.com/keen-wolf)).

#### Experimental feature

* Add experimental `Replicated` database engine. It replicates DDL queries across multiple hosts. [#16193](https://github.com/ClickHouse/ClickHouse/pull/16193) ([tavplubix](https://github.com/tavplubix)).
* Introduce experimental support for window functions, enabled with `allow_experimental_window_functions = 1`. This is a preliminary, alpha-quality implementation that is not suitable for production use and will change in backward-incompatible ways in future releases. Please see [the documentation](https://github.com/ClickHouse/ClickHouse/blob/master/docs/en/sql-reference/window-functions/index.md#experimental-window-functions) for the list of supported features. [#20337](https://github.com/ClickHouse/ClickHouse/pull/20337) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Add the ability to backup/restore metadata files for DiskS3. [#18377](https://github.com/ClickHouse/ClickHouse/pull/18377) ([Pavel Kovalenko](https://github.com/Jokser)).

#### Performance Improvement

* Hedged requests for remote queries. When setting `use_hedged_requests` enabled (off by default), allow to establish many connections with different replicas for query. New connection is enabled in case existent connection(s) with replica(s) were not established within `hedged_connection_timeout` or no data was received within `receive_data_timeout`. Query uses the first connection which send non empty progress packet (or data packet, if `allow_changing_replica_until_first_data_packet`); other connections are cancelled. Queries with `max_parallel_replicas > 1` are supported. [#19291](https://github.com/ClickHouse/ClickHouse/pull/19291) ([Kruglov Pavel](https://github.com/Avogar)). This allows to significantly reduce tail latencies on very large clusters.
* Added support for `PREWHERE` (and enable the corresponding optimization) when tables have row-level security expressions specified. [#19576](https://github.com/ClickHouse/ClickHouse/pull/19576) ([Denis Glazachev](https://github.com/traceon)).
* The setting `distributed_aggregation_memory_efficient` is enabled by default. It will lower memory usage and improve performance of distributed queries. [#20599](https://github.com/ClickHouse/ClickHouse/pull/20599) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Improve performance of GROUP BY multiple fixed size keys. [#20472](https://github.com/ClickHouse/ClickHouse/pull/20472) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Improve performance of aggregate functions by more strict aliasing. [#19946](https://github.com/ClickHouse/ClickHouse/pull/19946) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Speed up reading from `Memory` tables in extreme cases (when reading speed is in order of 50 GB/sec) by simplification of pipeline and (consequently) less lock contention in pipeline scheduling. [#20468](https://github.com/ClickHouse/ClickHouse/pull/20468) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Partially reimplement HTTP server to make it making less copies of incoming and outgoing data. It gives up to 1.5 performance improvement on inserting long records over HTTP. [#19516](https://github.com/ClickHouse/ClickHouse/pull/19516) ([Ivan](https://github.com/abyss7)).
* Add `compress` setting for `Memory` tables. If it's enabled the table will use less RAM. On some machines and datasets it can also work faster on SELECT, but it is not always the case. This closes [#20093](https://github.com/ClickHouse/ClickHouse/issues/20093). Note: there are reasons why Memory tables can work slower than MergeTree: (1) lack of compression (2) static size of blocks (3) lack of indices and prewhere... [#20168](https://github.com/ClickHouse/ClickHouse/pull/20168) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Slightly better code in aggregation. [#20978](https://github.com/ClickHouse/ClickHouse/pull/20978) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add back `intDiv`/`modulo` specializations for better performance. This fixes [#21293](https://github.com/ClickHouse/ClickHouse/issues/21293) . The regression was introduced in https://github.com/ClickHouse/ClickHouse/pull/18145 . [#21307](https://github.com/ClickHouse/ClickHouse/pull/21307) ([Amos Bird](https://github.com/amosbird)).
* Do not squash blocks too much on INSERT SELECT if inserting into Memory table. In previous versions inefficient data representation was created in Memory table after INSERT SELECT. This closes [#13052](https://github.com/ClickHouse/ClickHouse/issues/13052). [#20169](https://github.com/ClickHouse/ClickHouse/pull/20169) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix at least one case when DataType parser may have exponential complexity (found by fuzzer). This closes [#20096](https://github.com/ClickHouse/ClickHouse/issues/20096). [#20132](https://github.com/ClickHouse/ClickHouse/pull/20132) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Parallelize SELECT with FINAL for single part with level > 0 when `do_not_merge_across_partitions_select_final` setting is 1. [#19375](https://github.com/ClickHouse/ClickHouse/pull/19375) ([Kruglov Pavel](https://github.com/Avogar)).
* Fill only requested columns when querying `system.parts` and `system.parts_columns`. Closes [#19570](https://github.com/ClickHouse/ClickHouse/issues/19570). [#21035](https://github.com/ClickHouse/ClickHouse/pull/21035) ([Anmol Arora](https://github.com/anmolarora)).
* Perform algebraic optimizations of arithmetic expressions inside `avg` aggregate function. close [#20092](https://github.com/ClickHouse/ClickHouse/issues/20092). [#20183](https://github.com/ClickHouse/ClickHouse/pull/20183) ([flynn](https://github.com/ucasFL)).

#### Improvement

* Case-insensitive compression methods for table functions. Also fixed LZMA compression method which was checked in upper case. [#21416](https://github.com/ClickHouse/ClickHouse/pull/21416) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Add two settings to delay or throw error during insertion when there are too many inactive parts. This is useful when server fails to clean up parts quickly enough. [#20178](https://github.com/ClickHouse/ClickHouse/pull/20178) ([Amos Bird](https://github.com/amosbird)).
* Provide better compatibility for mysql clients. 1. mysql jdbc 2. mycli. [#21367](https://github.com/ClickHouse/ClickHouse/pull/21367) ([Amos Bird](https://github.com/amosbird)).
* Forbid to drop a column if it's referenced by materialized view. Closes [#21164](https://github.com/ClickHouse/ClickHouse/issues/21164). [#21303](https://github.com/ClickHouse/ClickHouse/pull/21303) ([flynn](https://github.com/ucasFL)).
* MySQL dictionary source will now retry unexpected connection failures (Lost connection to MySQL server during query) which sometimes happen on SSL/TLS connections. [#21237](https://github.com/ClickHouse/ClickHouse/pull/21237) ([Alexander Kazakov](https://github.com/Akazz)).
* Usability improvement: more consistent `DateTime64` parsing: recognize the case when unix timestamp with subsecond resolution is specified as scaled integer (like `1111111111222` instead of `1111111111.222`). This closes [#13194](https://github.com/ClickHouse/ClickHouse/issues/13194). [#21053](https://github.com/ClickHouse/ClickHouse/pull/21053) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Do only merging of sorted blocks on initiator with distributed_group_by_no_merge. [#20882](https://github.com/ClickHouse/ClickHouse/pull/20882) ([Azat Khuzhin](https://github.com/azat)).
* When loading config for mysql source ClickHouse will now randomize the list of replicas with the same priority to ensure the round-robin logics of picking mysql endpoint. This closes [#20629](https://github.com/ClickHouse/ClickHouse/issues/20629). [#20632](https://github.com/ClickHouse/ClickHouse/pull/20632) ([Alexander Kazakov](https://github.com/Akazz)).
* Function 'reinterpretAs(x, Type)' renamed into 'reinterpret(x, Type)'. [#20611](https://github.com/ClickHouse/ClickHouse/pull/20611) ([Maksim Kita](https://github.com/kitaisreal)).
* Support vhost for RabbitMQ engine [#20576](https://github.com/ClickHouse/ClickHouse/issues/20576). [#20596](https://github.com/ClickHouse/ClickHouse/pull/20596) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Improved serialization for data types combined of Arrays and Tuples. Improved matching enum data types to protobuf enum type. Fixed serialization of the `Map` data type. Omitted values are now set by default. [#20506](https://github.com/ClickHouse/ClickHouse/pull/20506) ([Vitaly Baranov](https://github.com/vitlibar)).
* Fixed race between execution of distributed DDL tasks and cleanup of DDL queue. Now DDL task cannot be removed from ZooKeeper if there are active workers. Fixes [#20016](https://github.com/ClickHouse/ClickHouse/issues/20016). [#20448](https://github.com/ClickHouse/ClickHouse/pull/20448) ([tavplubix](https://github.com/tavplubix)).
* Make FQDN and other DNS related functions work correctly in alpine images. [#20336](https://github.com/ClickHouse/ClickHouse/pull/20336) ([filimonov](https://github.com/filimonov)).
* Do not allow early constant folding of explicitly forbidden functions. [#20303](https://github.com/ClickHouse/ClickHouse/pull/20303) ([Azat Khuzhin](https://github.com/azat)).
* Implicit conversion from integer to Decimal type might succeeded if integer value doe not fit into Decimal type. Now it throws `ARGUMENT_OUT_OF_BOUND`. [#20232](https://github.com/ClickHouse/ClickHouse/pull/20232) ([tavplubix](https://github.com/tavplubix)).
* Lockless `SYSTEM FLUSH DISTRIBUTED`. [#20215](https://github.com/ClickHouse/ClickHouse/pull/20215) ([Azat Khuzhin](https://github.com/azat)).
* Normalize count(constant), sum(1) to count(). This is needed for projection query routing. [#20175](https://github.com/ClickHouse/ClickHouse/pull/20175) ([Amos Bird](https://github.com/amosbird)).
* Support all native integer types in bitmap functions. [#20171](https://github.com/ClickHouse/ClickHouse/pull/20171) ([Amos Bird](https://github.com/amosbird)).
* Updated `CacheDictionary`, `ComplexCacheDictionary`, `SSDCacheDictionary`, `SSDComplexKeyDictionary` to use LRUHashMap as underlying index. [#20164](https://github.com/ClickHouse/ClickHouse/pull/20164) ([Maksim Kita](https://github.com/kitaisreal)).
* The setting `access_management` is now configurable on startup by providing `CLICKHOUSE_DEFAULT_ACCESS_MANAGEMENT`, defaults to disabled (`0`) which was the prior value. [#20139](https://github.com/ClickHouse/ClickHouse/pull/20139) ([Marquitos](https://github.com/sonirico)).
* Fix toDateTime64(toDate()/toDateTime()) for DateTime64 - Implement DateTime64 clamping to match DateTime behaviour. [#20131](https://github.com/ClickHouse/ClickHouse/pull/20131) ([Azat Khuzhin](https://github.com/azat)).
* Quota improvements: SHOW TABLES is now considered as one query in the quota calculations, not two queries. SYSTEM queries now consume quota. Fix calculation of interval's end in quota consumption. [#20106](https://github.com/ClickHouse/ClickHouse/pull/20106) ([Vitaly Baranov](https://github.com/vitlibar)).
* Supports `path IN (set)` expressions for `system.zookeeper` table. [#20105](https://github.com/ClickHouse/ClickHouse/pull/20105) ([小路](https://github.com/nicelulu)).
* Show full details of `MaterializeMySQL` tables in `system.tables`. [#20051](https://github.com/ClickHouse/ClickHouse/pull/20051) ([Stig Bakken](https://github.com/stigsb)).
* Fix data race in executable dictionary that was possible only on misuse (when the script returns data ignoring its input). [#20045](https://github.com/ClickHouse/ClickHouse/pull/20045) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* The value of MYSQL_OPT_RECONNECT option can now be controlled by "opt_reconnect" parameter in the config section of mysql replica. [#19998](https://github.com/ClickHouse/ClickHouse/pull/19998) ([Alexander Kazakov](https://github.com/Akazz)).
* If user calls `JSONExtract` function with `Float32` type requested, allow inaccurate conversion to the result type. For example the number `0.1` in JSON is double precision and is not representable in Float32, but the user still wants to get it. Previous versions return 0 for non-Nullable type and NULL for Nullable type to indicate that conversion is imprecise. The logic was 100% correct but it was surprising to users and leading to questions. This closes [#13962](https://github.com/ClickHouse/ClickHouse/issues/13962). [#19960](https://github.com/ClickHouse/ClickHouse/pull/19960) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add conversion of block structure for INSERT into Distributed tables if it does not match. [#19947](https://github.com/ClickHouse/ClickHouse/pull/19947) ([Azat Khuzhin](https://github.com/azat)).
* Improvement for the `system.distributed_ddl_queue` table. Initialize MaxDDLEntryID to the last value after restarting. Before this PR, MaxDDLEntryID will remain zero until a new DDLTask is processed. [#19924](https://github.com/ClickHouse/ClickHouse/pull/19924) ([Amos Bird](https://github.com/amosbird)).
* Show `MaterializeMySQL` tables in `system.parts`. [#19770](https://github.com/ClickHouse/ClickHouse/pull/19770) ([Stig Bakken](https://github.com/stigsb)).
* Add separate config directive for `Buffer` profile. [#19721](https://github.com/ClickHouse/ClickHouse/pull/19721) ([Azat Khuzhin](https://github.com/azat)).
* Move conditions that are not related to JOIN to WHERE clause. [#18720](https://github.com/ClickHouse/ClickHouse/issues/18720). [#19685](https://github.com/ClickHouse/ClickHouse/pull/19685) ([hexiaoting](https://github.com/hexiaoting)).
* Add ability to throttle INSERT into Distributed based on amount of pending bytes for async send (`bytes_to_delay_insert`/`max_delay_to_insert` and `bytes_to_throw_insert` settings for `Distributed` engine has been added). [#19673](https://github.com/ClickHouse/ClickHouse/pull/19673) ([Azat Khuzhin](https://github.com/azat)).
* Fix some rare cases when write errors can be ignored in destructors. [#19451](https://github.com/ClickHouse/ClickHouse/pull/19451) ([Azat Khuzhin](https://github.com/azat)).
* Print inline frames in stack traces for fatal errors. [#19317](https://github.com/ClickHouse/ClickHouse/pull/19317) ([Ivan](https://github.com/abyss7)).

#### Bug Fix

* Fix redundant reconnects to ZooKeeper and the possibility of two active sessions for a single clickhouse server. Both problems introduced in #14678. [#21264](https://github.com/ClickHouse/ClickHouse/pull/21264) ([alesapin](https://github.com/alesapin)).
* Fix error `Bad cast from type ... to DB::ColumnLowCardinality` while inserting into table with `LowCardinality` column from `Values` format. Fixes #21140 [#21357](https://github.com/ClickHouse/ClickHouse/pull/21357) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix a deadlock in `ALTER DELETE` mutations for non replicated MergeTree table engines when the predicate contains the table itself. Fixes [#20558](https://github.com/ClickHouse/ClickHouse/issues/20558). [#21477](https://github.com/ClickHouse/ClickHouse/pull/21477) ([alesapin](https://github.com/alesapin)).
* Fix SIGSEGV for distributed queries on failures. [#21434](https://github.com/ClickHouse/ClickHouse/pull/21434) ([Azat Khuzhin](https://github.com/azat)).
* Now `ALTER MODIFY COLUMN` queries will correctly affect changes in partition key, skip indices, TTLs, and so on. Fixes [#13675](https://github.com/ClickHouse/ClickHouse/issues/13675). [#21334](https://github.com/ClickHouse/ClickHouse/pull/21334) ([alesapin](https://github.com/alesapin)).
* Fix bug with `join_use_nulls` and joining `TOTALS` from subqueries. This closes [#19362](https://github.com/ClickHouse/ClickHouse/issues/19362) and [#21137](https://github.com/ClickHouse/ClickHouse/issues/21137). [#21248](https://github.com/ClickHouse/ClickHouse/pull/21248) ([vdimir](https://github.com/vdimir)).
* Fix crash in `EXPLAIN` for query with `UNION`. Fixes [#20876](https://github.com/ClickHouse/ClickHouse/issues/20876), [#21170](https://github.com/ClickHouse/ClickHouse/issues/21170). [#21246](https://github.com/ClickHouse/ClickHouse/pull/21246) ([flynn](https://github.com/ucasFL)).
* Now mutations allowed only for table engines that support them (MergeTree family, Memory, MaterializedView). Other engines will report a more clear error. Fixes [#21168](https://github.com/ClickHouse/ClickHouse/issues/21168). [#21183](https://github.com/ClickHouse/ClickHouse/pull/21183) ([alesapin](https://github.com/alesapin)).
* Fixes [#21112](https://github.com/ClickHouse/ClickHouse/issues/21112). Fixed bug that could cause duplicates with insert query (if one of the callbacks came a little too late). [#21138](https://github.com/ClickHouse/ClickHouse/pull/21138) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Fix `input_format_null_as_default` take effective when types are nullable. This fixes [#21116](https://github.com/ClickHouse/ClickHouse/issues/21116) . [#21121](https://github.com/ClickHouse/ClickHouse/pull/21121) ([Amos Bird](https://github.com/amosbird)).
* fix bug related to cast Tuple to Map. Closes [#21029](https://github.com/ClickHouse/ClickHouse/issues/21029). [#21120](https://github.com/ClickHouse/ClickHouse/pull/21120) ([hexiaoting](https://github.com/hexiaoting)).
* Fix the metadata leak when the Replicated*MergeTree with custom (non default) ZooKeeper cluster is dropped. [#21119](https://github.com/ClickHouse/ClickHouse/pull/21119) ([fastio](https://github.com/fastio)).
* Fix type mismatch issue when using LowCardinality keys in joinGet. This fixes [#21114](https://github.com/ClickHouse/ClickHouse/issues/21114). [#21117](https://github.com/ClickHouse/ClickHouse/pull/21117) ([Amos Bird](https://github.com/amosbird)).
* fix default_replica_path and default_replica_name values are useless on Replicated(*)MergeTree engine when the engine needs specify other parameters. [#21060](https://github.com/ClickHouse/ClickHouse/pull/21060) ([mxzlxy](https://github.com/mxzlxy)).
* Out of bound memory access was possible when formatting specifically crafted out of range value of type `DateTime64`. This closes [#20494](https://github.com/ClickHouse/ClickHouse/issues/20494). This closes [#20543](https://github.com/ClickHouse/ClickHouse/issues/20543). [#21023](https://github.com/ClickHouse/ClickHouse/pull/21023) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Block parallel insertions into storage join. [#21009](https://github.com/ClickHouse/ClickHouse/pull/21009) ([vdimir](https://github.com/vdimir)).
* Fixed behaviour, when `ALTER MODIFY COLUMN` created mutation, that will knowingly fail. [#21007](https://github.com/ClickHouse/ClickHouse/pull/21007) ([Anton Popov](https://github.com/CurtizJ)).
* Closes [#9969](https://github.com/ClickHouse/ClickHouse/issues/9969). Fixed Brotli http compression error, which reproduced for large data sizes, slightly complicated structure and with json output format. Update Brotli to the latest version to include the "fix rare access to uninitialized data in ring-buffer". [#20991](https://github.com/ClickHouse/ClickHouse/pull/20991) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Fix 'Empty task was returned from async task queue' on query cancellation. [#20881](https://github.com/ClickHouse/ClickHouse/pull/20881) ([Azat Khuzhin](https://github.com/azat)).
* `USE database;` query did not work when using MySQL 5.7 client to connect to ClickHouse server, it's fixed. Fixes [#18926](https://github.com/ClickHouse/ClickHouse/issues/18926). [#20878](https://github.com/ClickHouse/ClickHouse/pull/20878) ([tavplubix](https://github.com/tavplubix)).
* Fix usage of `-Distinct` combinator with `-State` combinator in aggregate functions. [#20866](https://github.com/ClickHouse/ClickHouse/pull/20866) ([Anton Popov](https://github.com/CurtizJ)).
* Fix subquery with union distinct and limit clause. close [#20597](https://github.com/ClickHouse/ClickHouse/issues/20597). [#20610](https://github.com/ClickHouse/ClickHouse/pull/20610) ([flynn](https://github.com/ucasFL)).
* Fixed inconsistent behavior of dictionary in case of queries where we look for absent keys in dictionary. [#20578](https://github.com/ClickHouse/ClickHouse/pull/20578) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Fix the number of threads for scalar subqueries and subqueries for index (after [#19007](https://github.com/ClickHouse/ClickHouse/issues/19007) single thread was always used). Fixes [#20457](https://github.com/ClickHouse/ClickHouse/issues/20457), [#20512](https://github.com/ClickHouse/ClickHouse/issues/20512). [#20550](https://github.com/ClickHouse/ClickHouse/pull/20550) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix crash which could happen if unknown packet was received from remove query (was introduced in [#17868](https://github.com/ClickHouse/ClickHouse/issues/17868)). [#20547](https://github.com/ClickHouse/ClickHouse/pull/20547) ([Azat Khuzhin](https://github.com/azat)).
* Add proper checks while parsing directory names for async INSERT (fixes SIGSEGV). [#20498](https://github.com/ClickHouse/ClickHouse/pull/20498) ([Azat Khuzhin](https://github.com/azat)).
* Fix function `transform` does not work properly for floating point keys. Closes [#20460](https://github.com/ClickHouse/ClickHouse/issues/20460). [#20479](https://github.com/ClickHouse/ClickHouse/pull/20479) ([flynn](https://github.com/ucasFL)).
* Fix infinite loop when propagating WITH aliases to subqueries. This fixes [#20388](https://github.com/ClickHouse/ClickHouse/issues/20388). [#20476](https://github.com/ClickHouse/ClickHouse/pull/20476) ([Amos Bird](https://github.com/amosbird)).
* Fix abnormal server termination when http client goes away. [#20464](https://github.com/ClickHouse/ClickHouse/pull/20464) ([Azat Khuzhin](https://github.com/azat)).
* Fix `LOGICAL_ERROR` for `join_use_nulls=1` when JOIN contains const from SELECT. [#20461](https://github.com/ClickHouse/ClickHouse/pull/20461) ([Azat Khuzhin](https://github.com/azat)).
* Check if table function `view` is used in expression list and throw an error. This fixes [#20342](https://github.com/ClickHouse/ClickHouse/issues/20342). [#20350](https://github.com/ClickHouse/ClickHouse/pull/20350) ([Amos Bird](https://github.com/amosbird)).
* Avoid invalid dereference in RANGE_HASHED() dictionary. [#20345](https://github.com/ClickHouse/ClickHouse/pull/20345) ([Azat Khuzhin](https://github.com/azat)).
* Fix null dereference with `join_use_nulls=1`. [#20344](https://github.com/ClickHouse/ClickHouse/pull/20344) ([Azat Khuzhin](https://github.com/azat)).
* Fix incorrect result of binary operations between two constant decimals of different scale. Fixes [#20283](https://github.com/ClickHouse/ClickHouse/issues/20283). [#20339](https://github.com/ClickHouse/ClickHouse/pull/20339) ([Maksim Kita](https://github.com/kitaisreal)).
* Fix too often retries of failed background tasks for `ReplicatedMergeTree` table engines family. This could lead to too verbose logging and increased CPU load. Fixes [#20203](https://github.com/ClickHouse/ClickHouse/issues/20203). [#20335](https://github.com/ClickHouse/ClickHouse/pull/20335) ([alesapin](https://github.com/alesapin)).
* Restrict to `DROP` or `RENAME` version column of `*CollapsingMergeTree` and `ReplacingMergeTree` table engines. [#20300](https://github.com/ClickHouse/ClickHouse/pull/20300) ([alesapin](https://github.com/alesapin)).
* Fixed the behavior when in case of broken JSON we tried to read the whole file into memory which leads to exception from the allocator. Fixes [#19719](https://github.com/ClickHouse/ClickHouse/issues/19719). [#20286](https://github.com/ClickHouse/ClickHouse/pull/20286) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Fix exception during vertical merge for `MergeTree` table engines family which don't allow to perform vertical merges. Fixes [#20259](https://github.com/ClickHouse/ClickHouse/issues/20259). [#20279](https://github.com/ClickHouse/ClickHouse/pull/20279) ([alesapin](https://github.com/alesapin)).
* Fix rare server crash on config reload during the shutdown. Fixes [#19689](https://github.com/ClickHouse/ClickHouse/issues/19689). [#20224](https://github.com/ClickHouse/ClickHouse/pull/20224) ([alesapin](https://github.com/alesapin)).
* Fix CTE when using in INSERT SELECT. This fixes [#20187](https://github.com/ClickHouse/ClickHouse/issues/20187), fixes [#20195](https://github.com/ClickHouse/ClickHouse/issues/20195). [#20211](https://github.com/ClickHouse/ClickHouse/pull/20211) ([Amos Bird](https://github.com/amosbird)).
* Fixes [#19314](https://github.com/ClickHouse/ClickHouse/issues/19314). [#20156](https://github.com/ClickHouse/ClickHouse/pull/20156) ([Ivan](https://github.com/abyss7)).
* fix toMinute function to handle special timezone correctly. [#20149](https://github.com/ClickHouse/ClickHouse/pull/20149) ([keenwolf](https://github.com/keen-wolf)).
* Fix server crash after query with `if` function with `Tuple` type of then/else branches result. `Tuple` type must contain `Array` or another complex type. Fixes [#18356](https://github.com/ClickHouse/ClickHouse/issues/18356). [#20133](https://github.com/ClickHouse/ClickHouse/pull/20133) ([alesapin](https://github.com/alesapin)).
* The `MongoDB` table engine now establishes connection only when it's going to read data. `ATTACH TABLE` won't try to connect anymore. [#20110](https://github.com/ClickHouse/ClickHouse/pull/20110) ([Vitaly Baranov](https://github.com/vitlibar)).
* Bugfix in StorageJoin. [#20079](https://github.com/ClickHouse/ClickHouse/pull/20079) ([vdimir](https://github.com/vdimir)).
* Fix the case when calculating modulo of division of negative number by small divisor, the resulting data type was not large enough to accomodate the negative result. This closes [#20052](https://github.com/ClickHouse/ClickHouse/issues/20052). [#20067](https://github.com/ClickHouse/ClickHouse/pull/20067) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* MaterializeMySQL: Fix replication for statements that update several tables. [#20066](https://github.com/ClickHouse/ClickHouse/pull/20066) ([Håvard Kvålen](https://github.com/havardk)).
* Prevent "Connection refused" in docker during initialization script execution. [#20012](https://github.com/ClickHouse/ClickHouse/pull/20012) ([filimonov](https://github.com/filimonov)).
* `EmbeddedRocksDB` is an experimental storage. Fix the issue with lack of proper type checking. Simplified code. This closes [#19967](https://github.com/ClickHouse/ClickHouse/issues/19967). [#19972](https://github.com/ClickHouse/ClickHouse/pull/19972) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix a segfault in function `fromModifiedJulianDay` when the argument type is `Nullable(T)` for any integral types other than Int32. [#19959](https://github.com/ClickHouse/ClickHouse/pull/19959) ([PHO](https://github.com/depressed-pho)).
* BloomFilter index crash fix. Fixes [#19757](https://github.com/ClickHouse/ClickHouse/issues/19757). [#19884](https://github.com/ClickHouse/ClickHouse/pull/19884) ([Maksim Kita](https://github.com/kitaisreal)).
* Deadlock was possible if system.text_log is enabled. This fixes [#19874](https://github.com/ClickHouse/ClickHouse/issues/19874). [#19875](https://github.com/ClickHouse/ClickHouse/pull/19875) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix starting the server with tables having default expressions containing dictGet(). Allow getting return type of dictGet() without loading dictionary. [#19805](https://github.com/ClickHouse/ClickHouse/pull/19805) ([Vitaly Baranov](https://github.com/vitlibar)).
* Fix clickhouse-client abort exception while executing only `select`. [#19790](https://github.com/ClickHouse/ClickHouse/pull/19790) ([taiyang-li](https://github.com/taiyang-li)).
* Fix a bug that moving pieces to destination table may failed in case of launching multiple clickhouse-copiers. [#19743](https://github.com/ClickHouse/ClickHouse/pull/19743) ([madianjun](https://github.com/mdianjun)).
* Background thread which executes `ON CLUSTER` queries might hang waiting for dropped replicated table to do something. It's fixed. [#19684](https://github.com/ClickHouse/ClickHouse/pull/19684) ([yiguolei](https://github.com/yiguolei)).

#### Build/Testing/Packaging Improvement

* Allow to build ClickHouse with AVX-2 enabled globally. It gives slight performance benefits on modern CPUs. Not recommended for production and will not be supported as official build for now. [#20180](https://github.com/ClickHouse/ClickHouse/pull/20180) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix some of the issues found by Coverity. See [#19964](https://github.com/ClickHouse/ClickHouse/issues/19964). [#20010](https://github.com/ClickHouse/ClickHouse/pull/20010) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Allow to start up with modified binary under gdb. In previous version if you set up breakpoint in gdb before start, server will refuse to start up due to failed integrity check. [#21258](https://github.com/ClickHouse/ClickHouse/pull/21258) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add a test for different compression methods in Kafka. [#21111](https://github.com/ClickHouse/ClickHouse/pull/21111) ([filimonov](https://github.com/filimonov)).
* Fixed port clash from test_storage_kerberized_hdfs test. [#19974](https://github.com/ClickHouse/ClickHouse/pull/19974) ([Ilya Yatsishin](https://github.com/qoega)).
* Print `stdout` and `stderr` to log when failed to start docker in integration tests. Before this PR there was a very short error message in this case which didn't help to investigate the problems. [#20631](https://github.com/ClickHouse/ClickHouse/pull/20631) ([Vitaly Baranov](https://github.com/vitlibar)).


## ClickHouse release 21.2

### ClickHouse release v21.2.2.8-stable, 2021-02-07

#### Backward Incompatible Change

* Bitwise functions (`bitAnd`, `bitOr`, etc) are forbidden for floating point arguments. Now you have to do explicit cast to integer. [#19853](https://github.com/ClickHouse/ClickHouse/pull/19853) ([Azat Khuzhin](https://github.com/azat)).
* Forbid `lcm`/`gcd` for floats. [#19532](https://github.com/ClickHouse/ClickHouse/pull/19532) ([Azat Khuzhin](https://github.com/azat)).
* Fix memory tracking for `OPTIMIZE TABLE`/merges; account query memory limits and sampling for `OPTIMIZE TABLE`/merges. [#18772](https://github.com/ClickHouse/ClickHouse/pull/18772) ([Azat Khuzhin](https://github.com/azat)).
* Disallow floating point column as partition key, see [#18421](https://github.com/ClickHouse/ClickHouse/issues/18421#event-4147046255). [#18464](https://github.com/ClickHouse/ClickHouse/pull/18464) ([hexiaoting](https://github.com/hexiaoting)).
* Excessive parenthesis in type definitions no longer supported, example: `Array((UInt8))`.

#### New Feature

* Added `PostgreSQL` table engine (both select/insert, with support for multidimensional arrays), also as table function. Added `PostgreSQL` dictionary source. Added `PostgreSQL` database engine. [#18554](https://github.com/ClickHouse/ClickHouse/pull/18554) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Data type `Nested` now supports arbitrary levels of nesting. Introduced subcolumns of complex types, such as `size0` in `Array`, `null` in `Nullable`, names of `Tuple` elements, which can be read without reading of whole column. [#17310](https://github.com/ClickHouse/ClickHouse/pull/17310) ([Anton Popov](https://github.com/CurtizJ)).
* Added `Nullable` support for `FlatDictionary`, `HashedDictionary`, `ComplexKeyHashedDictionary`, `DirectDictionary`, `ComplexKeyDirectDictionary`, `RangeHashedDictionary`. [#18236](https://github.com/ClickHouse/ClickHouse/pull/18236) ([Maksim Kita](https://github.com/kitaisreal)).
* Adds a new table called `system.distributed_ddl_queue` that displays the queries in the DDL worker queue. [#17656](https://github.com/ClickHouse/ClickHouse/pull/17656) ([Bharat Nallan](https://github.com/bharatnc)).
* Added support of mapping LDAP group names, and attribute values in general, to local roles for users from ldap user directories. [#17211](https://github.com/ClickHouse/ClickHouse/pull/17211) ([Denis Glazachev](https://github.com/traceon)).
* Support insert into table function `cluster`, and for both table functions `remote` and `cluster`, support distributing data across nodes by specify sharding key. Close [#16752](https://github.com/ClickHouse/ClickHouse/issues/16752). [#18264](https://github.com/ClickHouse/ClickHouse/pull/18264) ([flynn](https://github.com/ucasFL)).
* Add function `decodeXMLComponent` to decode characters for XML. Example: `SELECT decodeXMLComponent('Hello,"world"!')` [#17659](https://github.com/ClickHouse/ClickHouse/issues/17659). [#18542](https://github.com/ClickHouse/ClickHouse/pull/18542) ([nauta](https://github.com/nautaa)).
* Added functions `parseDateTimeBestEffortUSOrZero`, `parseDateTimeBestEffortUSOrNull`. [#19712](https://github.com/ClickHouse/ClickHouse/pull/19712) ([Maksim Kita](https://github.com/kitaisreal)).
* Add `sign` math function. [#19527](https://github.com/ClickHouse/ClickHouse/pull/19527) ([flynn](https://github.com/ucasFL)).
* Add information about used features (functions, table engines, etc) into system.query_log. [#18495](https://github.com/ClickHouse/ClickHouse/issues/18495). [#19371](https://github.com/ClickHouse/ClickHouse/pull/19371) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Function `formatDateTime` support the `%Q` modification to format date to quarter. [#19224](https://github.com/ClickHouse/ClickHouse/pull/19224) ([Jianmei Zhang](https://github.com/zhangjmruc)).
* Support MetaKey+Enter hotkey binding in play UI. [#19012](https://github.com/ClickHouse/ClickHouse/pull/19012) ([sundyli](https://github.com/sundy-li)).
* Add three functions for map data type: 1. `mapContains(map, key)` to check weather map.keys include the second parameter key. 2. `mapKeys(map)` return all the keys in Array format 3. `mapValues(map)` return all the values in Array format. [#18788](https://github.com/ClickHouse/ClickHouse/pull/18788) ([hexiaoting](https://github.com/hexiaoting)).
* Add `log_comment` setting related to [#18494](https://github.com/ClickHouse/ClickHouse/issues/18494). [#18549](https://github.com/ClickHouse/ClickHouse/pull/18549) ([Zijie Lu](https://github.com/TszKitLo40)).
* Add support of tuple argument to `argMin` and `argMax` functions. [#17359](https://github.com/ClickHouse/ClickHouse/pull/17359) ([Ildus Kurbangaliev](https://github.com/ildus)).
* Support `EXISTS VIEW` syntax. [#18552](https://github.com/ClickHouse/ClickHouse/pull/18552) ([Du Chuan](https://github.com/spongedu)).
* Add `SELECT ALL` syntax. closes [#18706](https://github.com/ClickHouse/ClickHouse/issues/18706). [#18723](https://github.com/ClickHouse/ClickHouse/pull/18723) ([flynn](https://github.com/ucasFL)).

#### Performance Improvement

* Faster parts removal by lowering the number of `stat` syscalls. This returns the optimization that existed while ago. More safe interface of `IDisk`. This closes [#19065](https://github.com/ClickHouse/ClickHouse/issues/19065). [#19086](https://github.com/ClickHouse/ClickHouse/pull/19086) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Aliases declared in `WITH` statement are properly used in index analysis. Queries like `WITH column AS alias SELECT ... WHERE alias = ...` may use index now. [#18896](https://github.com/ClickHouse/ClickHouse/pull/18896) ([Amos Bird](https://github.com/amosbird)).
* Add `optimize_alias_column_prediction` (on by default), that will: - Respect aliased columns in WHERE during partition pruning and skipping data using secondary indexes; - Respect aliased columns in WHERE for trivial count queries for optimize_trivial_count; - Respect aliased columns in GROUP BY/ORDER BY for optimize_aggregation_in_order/optimize_read_in_order. [#16995](https://github.com/ClickHouse/ClickHouse/pull/16995) ([sundyli](https://github.com/sundy-li)).
* Speed up aggregate function `sum`. Improvement only visible on synthetic benchmarks and not very practical. [#19216](https://github.com/ClickHouse/ClickHouse/pull/19216) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Update libc++ and use another ABI to provide better performance. [#18914](https://github.com/ClickHouse/ClickHouse/pull/18914) ([Danila Kutenin](https://github.com/danlark1)).
* Rewrite `sumIf()` and `sum(if())` function to `countIf()` function when logically equivalent. [#17041](https://github.com/ClickHouse/ClickHouse/pull/17041) ([flynn](https://github.com/ucasFL)).
* Use a connection pool for S3 connections, controlled by the `s3_max_connections` settings. [#13405](https://github.com/ClickHouse/ClickHouse/pull/13405) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Add support for zstd long option for better compression of string columns to save space. [#17184](https://github.com/ClickHouse/ClickHouse/pull/17184) ([ygrek](https://github.com/ygrek)).
* Slightly improve server latency by removing access to configuration on every connection. [#19863](https://github.com/ClickHouse/ClickHouse/pull/19863) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Reduce lock contention for multiple layers of the `Buffer` engine. [#19379](https://github.com/ClickHouse/ClickHouse/pull/19379) ([Azat Khuzhin](https://github.com/azat)).
* Support splitting `Filter` step of query plan into `Expression + Filter` pair. Together with `Expression + Expression` merging optimization ([#17458](https://github.com/ClickHouse/ClickHouse/issues/17458)) it may delay execution for some expressions after `Filter` step. [#19253](https://github.com/ClickHouse/ClickHouse/pull/19253) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).

#### Improvement

* `SELECT count() FROM table` now can be executed if only one any column can be selected from the `table`. This PR fixes [#10639](https://github.com/ClickHouse/ClickHouse/issues/10639). [#18233](https://github.com/ClickHouse/ClickHouse/pull/18233) ([Vitaly Baranov](https://github.com/vitlibar)).
* Set charset to `utf8mb4` when interacting with remote MySQL servers. Fixes [#19795](https://github.com/ClickHouse/ClickHouse/issues/19795). [#19800](https://github.com/ClickHouse/ClickHouse/pull/19800) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* `S3` table function now supports `auto` compression mode (autodetect). This closes [#18754](https://github.com/ClickHouse/ClickHouse/issues/18754). [#19793](https://github.com/ClickHouse/ClickHouse/pull/19793) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Correctly output infinite arguments for `formatReadableTimeDelta` function. In previous versions, there was implicit conversion to implementation specific integer value. [#19791](https://github.com/ClickHouse/ClickHouse/pull/19791) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Table function `S3` will use global region if the region can't be determined exactly. This closes [#10998](https://github.com/ClickHouse/ClickHouse/issues/10998). [#19750](https://github.com/ClickHouse/ClickHouse/pull/19750) ([Vladimir Chebotarev](https://github.com/excitoon)).
* In distributed queries if the setting `async_socket_for_remote` is enabled, it was possible to get stack overflow at least in debug build configuration if very deeply nested data type is used in table (e.g. `Array(Array(Array(...more...)))`). This fixes [#19108](https://github.com/ClickHouse/ClickHouse/issues/19108). This change introduces minor backward incompatibility: excessive parenthesis in type definitions no longer supported, example: `Array((UInt8))`. [#19736](https://github.com/ClickHouse/ClickHouse/pull/19736) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add separate pool for message brokers (RabbitMQ and Kafka). [#19722](https://github.com/ClickHouse/ClickHouse/pull/19722) ([Azat Khuzhin](https://github.com/azat)).
* Fix rare `max_number_of_merges_with_ttl_in_pool` limit overrun (more merges with TTL can be assigned) for non-replicated MergeTree. [#19708](https://github.com/ClickHouse/ClickHouse/pull/19708) ([alesapin](https://github.com/alesapin)).
* Dictionary: better error message during attribute parsing. [#19678](https://github.com/ClickHouse/ClickHouse/pull/19678) ([Maksim Kita](https://github.com/kitaisreal)).
* Add an option to disable validation of checksums on reading. Should never be used in production. Please do not expect any benefits in disabling it. It may only be used for experiments and benchmarks. The setting only applicable for tables of MergeTree family. Checksums are always validated for other table engines and when receiving data over network. In my observations there is no performance difference or it is less than 0.5%. [#19588](https://github.com/ClickHouse/ClickHouse/pull/19588) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Support constant result in function `multiIf`. [#19533](https://github.com/ClickHouse/ClickHouse/pull/19533) ([Maksim Kita](https://github.com/kitaisreal)).
* Enable function length/empty/notEmpty for datatype Map, which returns keys number in Map. [#19530](https://github.com/ClickHouse/ClickHouse/pull/19530) ([taiyang-li](https://github.com/taiyang-li)).
* Add `--reconnect` option to `clickhouse-benchmark`. When this option is specified, it will reconnect before every request. This is needed for testing. [#19872](https://github.com/ClickHouse/ClickHouse/pull/19872) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Support using the new location of `.debug` file. This fixes [#19348](https://github.com/ClickHouse/ClickHouse/issues/19348). [#19520](https://github.com/ClickHouse/ClickHouse/pull/19520) ([Amos Bird](https://github.com/amosbird)).
* `toIPv6` function parses `IPv4` addresses. [#19518](https://github.com/ClickHouse/ClickHouse/pull/19518) ([Bharat Nallan](https://github.com/bharatnc)).
* Add `http_referer` field to `system.query_log`, `system.processes`, etc. This closes [#19389](https://github.com/ClickHouse/ClickHouse/issues/19389). [#19390](https://github.com/ClickHouse/ClickHouse/pull/19390) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Improve MySQL compatibility by making more functions case insensitive and adding aliases. [#19387](https://github.com/ClickHouse/ClickHouse/pull/19387) ([Daniil Kondratyev](https://github.com/dankondr)).
* Add metrics for MergeTree parts (Wide/Compact/InMemory) types. [#19381](https://github.com/ClickHouse/ClickHouse/pull/19381) ([Azat Khuzhin](https://github.com/azat)).
* Allow docker to be executed with arbitrary uid. [#19374](https://github.com/ClickHouse/ClickHouse/pull/19374) ([filimonov](https://github.com/filimonov)).
* Fix wrong alignment of values of `IPv4` data type in Pretty formats. They were aligned to the right, not to the left. This closes [#19184](https://github.com/ClickHouse/ClickHouse/issues/19184). [#19339](https://github.com/ClickHouse/ClickHouse/pull/19339) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Allow change `max_server_memory_usage` without restart. This closes [#18154](https://github.com/ClickHouse/ClickHouse/issues/18154). [#19186](https://github.com/ClickHouse/ClickHouse/pull/19186) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* The exception when function `bar` is called with certain NaN argument may be slightly misleading in previous versions. This fixes [#19088](https://github.com/ClickHouse/ClickHouse/issues/19088). [#19107](https://github.com/ClickHouse/ClickHouse/pull/19107) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Explicitly set uid / gid of clickhouse user & group to the fixed values (101) in clickhouse-server images. [#19096](https://github.com/ClickHouse/ClickHouse/pull/19096) ([filimonov](https://github.com/filimonov)).
* Fixed `PeekableReadBuffer: Memory limit exceed` error when inserting data with huge strings. Fixes [#18690](https://github.com/ClickHouse/ClickHouse/issues/18690). [#18979](https://github.com/ClickHouse/ClickHouse/pull/18979) ([tavplubix](https://github.com/tavplubix)).
* Docker image: several improvements for clickhouse-server entrypoint. [#18954](https://github.com/ClickHouse/ClickHouse/pull/18954) ([filimonov](https://github.com/filimonov)).
* Add `normalizeQueryKeepNames` and `normalizedQueryHashKeepNames` to normalize queries without masking long names with `?`. This helps better analyze complex query logs. [#18910](https://github.com/ClickHouse/ClickHouse/pull/18910) ([Amos Bird](https://github.com/amosbird)).
* Check per-block checksum of the distributed batch on the sender before sending (without reading the file twice, the checksums will be verified while reading), this will avoid stuck of the INSERT on the receiver (on truncated .bin file on the sender). Avoid reading .bin files twice for batched INSERT (it was required to calculate rows/bytes to take squashing into account, now this information included into the header, backward compatible is preserved). [#18853](https://github.com/ClickHouse/ClickHouse/pull/18853) ([Azat Khuzhin](https://github.com/azat)).
* Fix issues with RIGHT and FULL JOIN of tables with aggregate function states. In previous versions exception about `cloneResized` method was thrown. [#18818](https://github.com/ClickHouse/ClickHouse/pull/18818) ([templarzq](https://github.com/templarzq)).
* Added prefix-based S3 endpoint settings. [#18812](https://github.com/ClickHouse/ClickHouse/pull/18812) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Add [UInt8, UInt16, UInt32, UInt64] arguments types support for bitmapTransform, bitmapSubsetInRange, bitmapSubsetLimit, bitmapContains functions. This closes [#18713](https://github.com/ClickHouse/ClickHouse/issues/18713). [#18791](https://github.com/ClickHouse/ClickHouse/pull/18791) ([sundyli](https://github.com/sundy-li)).
* Allow CTE (Common Table Expressions) to be further aliased. Propagate CSE (Common Subexpressions Elimination) to subqueries in the same level when `enable_global_with_statement = 1`. This fixes [#17378](https://github.com/ClickHouse/ClickHouse/issues/17378) . This fixes https://github.com/ClickHouse/ClickHouse/pull/16575#issuecomment-753416235 . [#18684](https://github.com/ClickHouse/ClickHouse/pull/18684) ([Amos Bird](https://github.com/amosbird)).
* Update librdkafka to v1.6.0-RC2. Fixes [#18668](https://github.com/ClickHouse/ClickHouse/issues/18668). [#18671](https://github.com/ClickHouse/ClickHouse/pull/18671) ([filimonov](https://github.com/filimonov)).
* In case of unexpected exceptions automatically restart background thread which is responsible for execution of distributed DDL queries. Fixes [#17991](https://github.com/ClickHouse/ClickHouse/issues/17991). [#18285](https://github.com/ClickHouse/ClickHouse/pull/18285) ([徐炘](https://github.com/weeds085490)).
* Updated AWS C++ SDK in order to utilize global regions in S3. [#17870](https://github.com/ClickHouse/ClickHouse/pull/17870) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Added support for `WITH ... [AND] [PERIODIC] REFRESH [interval_in_sec]` clause when creating `LIVE VIEW` tables. [#14822](https://github.com/ClickHouse/ClickHouse/pull/14822) ([vzakaznikov](https://github.com/vzakaznikov)).
* Restrict `MODIFY TTL` queries for `MergeTree` tables created in old syntax. Previously the query succeeded, but actually it had no effect. [#19064](https://github.com/ClickHouse/ClickHouse/pull/19064) ([Anton Popov](https://github.com/CurtizJ)).

#### Bug Fix

* Fix index analysis of binary functions with constant argument which leads to wrong query results. This fixes [#18364](https://github.com/ClickHouse/ClickHouse/issues/18364). [#18373](https://github.com/ClickHouse/ClickHouse/pull/18373) ([Amos Bird](https://github.com/amosbird)).
* Fix starting the server with tables having default expressions containing dictGet(). Allow getting return type of dictGet() without loading dictionary. [#19805](https://github.com/ClickHouse/ClickHouse/pull/19805) ([Vitaly Baranov](https://github.com/vitlibar)).
* Fix server crash after query with `if` function with `Tuple` type of then/else branches result. `Tuple` type must contain `Array` or another complex type. Fixes [#18356](https://github.com/ClickHouse/ClickHouse/issues/18356). [#20133](https://github.com/ClickHouse/ClickHouse/pull/20133) ([alesapin](https://github.com/alesapin)).
* `MaterializeMySQL` (experimental feature): Fix replication for statements that update several tables. [#20066](https://github.com/ClickHouse/ClickHouse/pull/20066) ([Håvard Kvålen](https://github.com/havardk)).
* Prevent "Connection refused" in docker during initialization script execution. [#20012](https://github.com/ClickHouse/ClickHouse/pull/20012) ([filimonov](https://github.com/filimonov)).
* `EmbeddedRocksDB` is an experimental storage. Fix the issue with lack of proper type checking. Simplified code. This closes [#19967](https://github.com/ClickHouse/ClickHouse/issues/19967). [#19972](https://github.com/ClickHouse/ClickHouse/pull/19972) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix a segfault in function `fromModifiedJulianDay` when the argument type is `Nullable(T)` for any integral types other than Int32. [#19959](https://github.com/ClickHouse/ClickHouse/pull/19959) ([PHO](https://github.com/depressed-pho)).
* The function `greatCircleAngle` returned inaccurate results in previous versions. This closes [#19769](https://github.com/ClickHouse/ClickHouse/issues/19769). [#19789](https://github.com/ClickHouse/ClickHouse/pull/19789) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix rare bug when some replicated operations (like mutation) cannot process some parts after data corruption. Fixes [#19593](https://github.com/ClickHouse/ClickHouse/issues/19593). [#19702](https://github.com/ClickHouse/ClickHouse/pull/19702) ([alesapin](https://github.com/alesapin)).
* Background thread which executes `ON CLUSTER` queries might hang waiting for dropped replicated table to do something. It's fixed. [#19684](https://github.com/ClickHouse/ClickHouse/pull/19684) ([yiguolei](https://github.com/yiguolei)).
* Fix wrong deserialization of columns description. It makes INSERT into a table with a column named `\` impossible. [#19479](https://github.com/ClickHouse/ClickHouse/pull/19479) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Mark distributed batch as broken in case of empty data block in one of files. [#19449](https://github.com/ClickHouse/ClickHouse/pull/19449) ([Azat Khuzhin](https://github.com/azat)).
* Fixed very rare bug that might cause mutation to hang after `DROP/DETACH/REPLACE/MOVE PARTITION`. It was partially fixed by [#15537](https://github.com/ClickHouse/ClickHouse/issues/15537) for the most cases. [#19443](https://github.com/ClickHouse/ClickHouse/pull/19443) ([tavplubix](https://github.com/tavplubix)).
* Fix possible error `Extremes transform was already added to pipeline`. Fixes [#14100](https://github.com/ClickHouse/ClickHouse/issues/14100). [#19430](https://github.com/ClickHouse/ClickHouse/pull/19430) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix default value in join types with non-zero default (e.g. some Enums). Closes [#18197](https://github.com/ClickHouse/ClickHouse/issues/18197). [#19360](https://github.com/ClickHouse/ClickHouse/pull/19360) ([vdimir](https://github.com/vdimir)).
* Do not mark file for distributed send as broken on EOF. [#19290](https://github.com/ClickHouse/ClickHouse/pull/19290) ([Azat Khuzhin](https://github.com/azat)).
* Fix leaking of pipe fd for `async_socket_for_remote`. [#19153](https://github.com/ClickHouse/ClickHouse/pull/19153) ([Azat Khuzhin](https://github.com/azat)).
* Fix infinite reading from file in `ORC` format (was introduced in [#10580](https://github.com/ClickHouse/ClickHouse/issues/10580)). Fixes [#19095](https://github.com/ClickHouse/ClickHouse/issues/19095). [#19134](https://github.com/ClickHouse/ClickHouse/pull/19134) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix issue in merge tree data writer which can lead to marks with bigger size than fixed granularity size. Fixes [#18913](https://github.com/ClickHouse/ClickHouse/issues/18913). [#19123](https://github.com/ClickHouse/ClickHouse/pull/19123) ([alesapin](https://github.com/alesapin)).
* Fix startup bug when clickhouse was not able to read compression codec from `LowCardinality(Nullable(...))` and throws exception `Attempt to read after EOF`. Fixes [#18340](https://github.com/ClickHouse/ClickHouse/issues/18340). [#19101](https://github.com/ClickHouse/ClickHouse/pull/19101) ([alesapin](https://github.com/alesapin)).
* Simplify the implementation of `tupleHammingDistance`. Support for tuples of any equal length. Fixes [#19029](https://github.com/ClickHouse/ClickHouse/issues/19029). [#19084](https://github.com/ClickHouse/ClickHouse/pull/19084) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Make sure `groupUniqArray` returns correct type for argument of Enum type. This closes [#17875](https://github.com/ClickHouse/ClickHouse/issues/17875). [#19019](https://github.com/ClickHouse/ClickHouse/pull/19019) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix possible error `Expected single dictionary argument for function` if use function `ignore` with `LowCardinality` argument. Fixes [#14275](https://github.com/ClickHouse/ClickHouse/issues/14275). [#19016](https://github.com/ClickHouse/ClickHouse/pull/19016) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix inserting of `LowCardinality` column to table with `TinyLog` engine. Fixes [#18629](https://github.com/ClickHouse/ClickHouse/issues/18629). [#19010](https://github.com/ClickHouse/ClickHouse/pull/19010) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix minor issue in JOIN: Join tries to materialize const columns, but our code waits for them in other places. [#18982](https://github.com/ClickHouse/ClickHouse/pull/18982) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Disable `optimize_move_functions_out_of_any` because optimization is not always correct. This closes [#18051](https://github.com/ClickHouse/ClickHouse/issues/18051). This closes [#18973](https://github.com/ClickHouse/ClickHouse/issues/18973). [#18981](https://github.com/ClickHouse/ClickHouse/pull/18981) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix possible exception `QueryPipeline stream: different number of columns` caused by merging of query plan's `Expression` steps. Fixes [#18190](https://github.com/ClickHouse/ClickHouse/issues/18190). [#18980](https://github.com/ClickHouse/ClickHouse/pull/18980) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fixed very rare deadlock at shutdown. [#18977](https://github.com/ClickHouse/ClickHouse/pull/18977) ([tavplubix](https://github.com/tavplubix)).
* Fixed rare crashes when server run out of memory. [#18976](https://github.com/ClickHouse/ClickHouse/pull/18976) ([tavplubix](https://github.com/tavplubix)).
* Fix incorrect behavior when `ALTER TABLE ... DROP PART 'part_name'` query removes all deduplication blocks for the whole partition. Fixes [#18874](https://github.com/ClickHouse/ClickHouse/issues/18874). [#18969](https://github.com/ClickHouse/ClickHouse/pull/18969) ([alesapin](https://github.com/alesapin)).
* Fixed issue [#18894](https://github.com/ClickHouse/ClickHouse/issues/18894) Add a check to avoid exception when long column alias('table.column' style, usually auto-generated by BI tools like Looker) equals to long table name. [#18968](https://github.com/ClickHouse/ClickHouse/pull/18968) ([Daniel Qin](https://github.com/mathfool)).
* Fix error `Task was not found in task queue` (possible only for remote queries, with `async_socket_for_remote = 1`). [#18964](https://github.com/ClickHouse/ClickHouse/pull/18964) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix bug when mutation with some escaped text (like `ALTER ... UPDATE e = CAST('foo', 'Enum8(\'foo\' = 1')` serialized incorrectly. Fixes [#18878](https://github.com/ClickHouse/ClickHouse/issues/18878). [#18944](https://github.com/ClickHouse/ClickHouse/pull/18944) ([alesapin](https://github.com/alesapin)).
* ATTACH PARTITION will reset mutations. [#18804](https://github.com/ClickHouse/ClickHouse/issues/18804). [#18935](https://github.com/ClickHouse/ClickHouse/pull/18935) ([fastio](https://github.com/fastio)).
* Fix issue with `bitmapOrCardinality` that may lead to nullptr dereference. This closes [#18911](https://github.com/ClickHouse/ClickHouse/issues/18911). [#18912](https://github.com/ClickHouse/ClickHouse/pull/18912) ([sundyli](https://github.com/sundy-li)).
* Fixed `Attempt to read after eof` error when trying to `CAST` `NULL` from `Nullable(String)` to `Nullable(Decimal(P, S))`. Now function `CAST` returns `NULL` when it cannot parse decimal from nullable string. Fixes [#7690](https://github.com/ClickHouse/ClickHouse/issues/7690). [#18718](https://github.com/ClickHouse/ClickHouse/pull/18718) ([Winter Zhang](https://github.com/zhang2014)).
* Fix data type convert issue for MySQL engine. [#18124](https://github.com/ClickHouse/ClickHouse/pull/18124) ([bo zeng](https://github.com/mis98zb)).
* Fix clickhouse-client abort exception while executing only `select`. [#19790](https://github.com/ClickHouse/ClickHouse/pull/19790) ([taiyang-li](https://github.com/taiyang-li)).


#### Build/Testing/Packaging Improvement

* Run [SQLancer](https://twitter.com/RiggerManuel/status/1352345625480884228) (logical SQL fuzzer) in CI. [#19006](https://github.com/ClickHouse/ClickHouse/pull/19006) ([Ilya Yatsishin](https://github.com/qoega)).
* Query Fuzzer will fuzz newly added tests more extensively. This closes [#18916](https://github.com/ClickHouse/ClickHouse/issues/18916). [#19185](https://github.com/ClickHouse/ClickHouse/pull/19185) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Integrate with [Big List of Naughty Strings](https://github.com/minimaxir/big-list-of-naughty-strings/) for better fuzzing. [#19480](https://github.com/ClickHouse/ClickHouse/pull/19480) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add integration tests run with MSan. [#18974](https://github.com/ClickHouse/ClickHouse/pull/18974) ([alesapin](https://github.com/alesapin)).
* Fixed MemorySanitizer errors in cyrus-sasl and musl. [#19821](https://github.com/ClickHouse/ClickHouse/pull/19821) ([Ilya Yatsishin](https://github.com/qoega)).
* Insuffiient arguments check in `positionCaseInsensitiveUTF8` function triggered address sanitizer. [#19720](https://github.com/ClickHouse/ClickHouse/pull/19720) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Remove --project-directory for docker-compose in integration test. Fix logs formatting from docker container. [#19706](https://github.com/ClickHouse/ClickHouse/pull/19706) ([Ilya Yatsishin](https://github.com/qoega)).
* Made generation of macros.xml easier for integration tests. No more excessive logging from dicttoxml. dicttoxml project is not active for 5+ years. [#19697](https://github.com/ClickHouse/ClickHouse/pull/19697) ([Ilya Yatsishin](https://github.com/qoega)).
* Allow to explicitly enable or disable watchdog via environment variable `CLICKHOUSE_WATCHDOG_ENABLE`. By default it is enabled if server is not attached to terminal. [#19522](https://github.com/ClickHouse/ClickHouse/pull/19522) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Allow building ClickHouse with Kafka support on arm64. [#19369](https://github.com/ClickHouse/ClickHouse/pull/19369) ([filimonov](https://github.com/filimonov)).
* Allow building librdkafka without ssl. [#19337](https://github.com/ClickHouse/ClickHouse/pull/19337) ([filimonov](https://github.com/filimonov)).
* Restore Kafka input in FreeBSD builds. [#18924](https://github.com/ClickHouse/ClickHouse/pull/18924) ([Alexandre Snarskii](https://github.com/snar)).
* Fix potential nullptr dereference in table function `VALUES`. [#19357](https://github.com/ClickHouse/ClickHouse/pull/19357) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Avoid UBSan reports in `arrayElement` function, `substring` and `arraySum`. Fixes [#19305](https://github.com/ClickHouse/ClickHouse/issues/19305). Fixes [#19287](https://github.com/ClickHouse/ClickHouse/issues/19287). This closes [#19336](https://github.com/ClickHouse/ClickHouse/issues/19336). [#19347](https://github.com/ClickHouse/ClickHouse/pull/19347) ([alexey-milovidov](https://github.com/alexey-milovidov)).


## ClickHouse release 21.1

### ClickHouse release v21.1.3.32-stable, 2021-02-03

#### Bug Fix

* BloomFilter index crash fix. Fixes [#19757](https://github.com/ClickHouse/ClickHouse/issues/19757). [#19884](https://github.com/ClickHouse/ClickHouse/pull/19884) ([Maksim Kita](https://github.com/kitaisreal)).
* Fix crash when pushing down predicates to union distinct subquery. This fixes [#19855](https://github.com/ClickHouse/ClickHouse/issues/19855). [#19861](https://github.com/ClickHouse/ClickHouse/pull/19861) ([Amos Bird](https://github.com/amosbird)).
* Fix filtering by UInt8 greater than 127. [#19799](https://github.com/ClickHouse/ClickHouse/pull/19799) ([Anton Popov](https://github.com/CurtizJ)).
* In previous versions, unusual arguments for function arrayEnumerateUniq may cause crash or infinite loop. This closes [#19787](https://github.com/ClickHouse/ClickHouse/issues/19787). [#19788](https://github.com/ClickHouse/ClickHouse/pull/19788) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fixed stack overflow when using accurate comparison of arithmetic type with string type. [#19773](https://github.com/ClickHouse/ClickHouse/pull/19773) ([tavplubix](https://github.com/tavplubix)).
* Fix crash when nested column name was used in `WHERE` or `PREWHERE`. Fixes [#19755](https://github.com/ClickHouse/ClickHouse/issues/19755). [#19763](https://github.com/ClickHouse/ClickHouse/pull/19763) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix a segmentation fault in `bitmapAndnot` function. Fixes [#19668](https://github.com/ClickHouse/ClickHouse/issues/19668). [#19713](https://github.com/ClickHouse/ClickHouse/pull/19713) ([Maksim Kita](https://github.com/kitaisreal)).
* Some functions with big integers may cause segfault. Big integers is experimental feature. This closes [#19667](https://github.com/ClickHouse/ClickHouse/issues/19667). [#19672](https://github.com/ClickHouse/ClickHouse/pull/19672) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix wrong result of function `neighbor` for `LowCardinality` argument. Fixes [#10333](https://github.com/ClickHouse/ClickHouse/issues/10333). [#19617](https://github.com/ClickHouse/ClickHouse/pull/19617) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix use-after-free of the CompressedWriteBuffer in Connection after disconnect. [#19599](https://github.com/ClickHouse/ClickHouse/pull/19599) ([Azat Khuzhin](https://github.com/azat)).
* `DROP/DETACH TABLE table ON CLUSTER cluster SYNC` query might hang, it's fixed. Fixes [#19568](https://github.com/ClickHouse/ClickHouse/issues/19568). [#19572](https://github.com/ClickHouse/ClickHouse/pull/19572) ([tavplubix](https://github.com/tavplubix)).
* Query CREATE DICTIONARY id expression fix. [#19571](https://github.com/ClickHouse/ClickHouse/pull/19571) ([Maksim Kita](https://github.com/kitaisreal)).
* Fix SIGSEGV with merge_tree_min_rows_for_concurrent_read/merge_tree_min_bytes_for_concurrent_read=0/UINT64_MAX. [#19528](https://github.com/ClickHouse/ClickHouse/pull/19528) ([Azat Khuzhin](https://github.com/azat)).
* Buffer overflow (on memory read) was possible if `addMonth` function was called with specifically crafted arguments. This fixes [#19441](https://github.com/ClickHouse/ClickHouse/issues/19441). This fixes [#19413](https://github.com/ClickHouse/ClickHouse/issues/19413). [#19472](https://github.com/ClickHouse/ClickHouse/pull/19472) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Uninitialized memory read was possible in encrypt/decrypt functions if empty string was passed as IV. This closes [#19391](https://github.com/ClickHouse/ClickHouse/issues/19391). [#19397](https://github.com/ClickHouse/ClickHouse/pull/19397) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix possible buffer overflow in Uber H3 library. See https://github.com/uber/h3/issues/392. This closes [#19219](https://github.com/ClickHouse/ClickHouse/issues/19219). [#19383](https://github.com/ClickHouse/ClickHouse/pull/19383) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix system.parts _state column (LOGICAL_ERROR when querying this column, due to incorrect order). [#19346](https://github.com/ClickHouse/ClickHouse/pull/19346) ([Azat Khuzhin](https://github.com/azat)).
* Fixed possible wrong result or segfault on aggregation when Materialized View and its target table have different structure. Fixes [#18063](https://github.com/ClickHouse/ClickHouse/issues/18063). [#19322](https://github.com/ClickHouse/ClickHouse/pull/19322) ([tavplubix](https://github.com/tavplubix)).
* Fix error `Cannot convert column now64() because it is constant but values of constants are different in source and result`. Continuation of [#7156](https://github.com/ClickHouse/ClickHouse/issues/7156). [#19316](https://github.com/ClickHouse/ClickHouse/pull/19316) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix bug when concurrent `ALTER` and `DROP` queries may hang while processing ReplicatedMergeTree table. [#19237](https://github.com/ClickHouse/ClickHouse/pull/19237) ([alesapin](https://github.com/alesapin)).
* Fixed `There is no checkpoint` error when inserting data through http interface using `Template` or `CustomSeparated` format. Fixes [#19021](https://github.com/ClickHouse/ClickHouse/issues/19021). [#19072](https://github.com/ClickHouse/ClickHouse/pull/19072) ([tavplubix](https://github.com/tavplubix)).
* Disable constant folding for subqueries on the analysis stage, when the result cannot be calculated. [#18446](https://github.com/ClickHouse/ClickHouse/pull/18446) ([Azat Khuzhin](https://github.com/azat)).
* Mutation might hang waiting for some non-existent part after `MOVE` or `REPLACE PARTITION` or, in rare cases, after `DETACH` or `DROP PARTITION`. It's fixed. [#15537](https://github.com/ClickHouse/ClickHouse/pull/15537) ([tavplubix](https://github.com/tavplubix)).



### ClickHouse release v21.1.2.15-stable 2021-01-18

#### Backward Incompatible Change

* The setting `input_format_null_as_default` is enabled by default. [#17525](https://github.com/ClickHouse/ClickHouse/pull/17525) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Check settings constraints for profile settings from config. Server will fail to start if users.xml contain settings that do not meet corresponding constraints. [#18486](https://github.com/ClickHouse/ClickHouse/pull/18486) ([tavplubix](https://github.com/tavplubix)).
* Restrict `ALTER MODIFY SETTING` from changing storage settings that affects data parts (`write_final_mark` and `enable_mixed_granularity_parts`). [#18306](https://github.com/ClickHouse/ClickHouse/pull/18306) ([Amos Bird](https://github.com/amosbird)).
* Set `insert_quorum_parallel` to 1 by default. It is significantly more convenient to use than "sequential" quorum inserts. But if you rely to sequential consistency, you should set the setting back to zero. [#17567](https://github.com/ClickHouse/ClickHouse/pull/17567) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Remove `sumburConsistentHash` function. This closes [#18120](https://github.com/ClickHouse/ClickHouse/issues/18120). [#18656](https://github.com/ClickHouse/ClickHouse/pull/18656) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Removed aggregate functions `timeSeriesGroupSum`, `timeSeriesGroupRateSum` because a friend of mine said they never worked. This fixes [#16869](https://github.com/ClickHouse/ClickHouse/issues/16869). If you have luck using these functions, write a email to clickhouse-feedback@yandex-team.com. [#17423](https://github.com/ClickHouse/ClickHouse/pull/17423) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Prohibit toUnixTimestamp(Date()) (before it just returns UInt16 representation of Date). [#17376](https://github.com/ClickHouse/ClickHouse/pull/17376) ([Azat Khuzhin](https://github.com/azat)).
* Allow using extended integer types (`Int128`, `Int256`, `UInt256`) in `avg` and `avgWeighted` functions. Also allow using different types (integer, decimal, floating point) for value and for weight in `avgWeighted` function. This is a backward-incompatible change: now the `avg` and `avgWeighted` functions always return `Float64` (as documented). Before this change the return type for `Decimal` arguments was also `Decimal`. [#15419](https://github.com/ClickHouse/ClickHouse/pull/15419) ([Mike](https://github.com/myrrc)).
* Expression `toUUID(N)` no longer works. Replace with `toUUID('00000000-0000-0000-0000-000000000000')`. This change is motivated by non-obvious results of `toUUID(N)` where N is non zero.
* SSL Certificates with incorrect "key usage" are rejected. In previous versions they are used to work. See [#19262](https://github.com/ClickHouse/ClickHouse/issues/19262).

#### New Feature

* Implement gRPC protocol in ClickHouse. [#15111](https://github.com/ClickHouse/ClickHouse/pull/15111) ([Vitaly Baranov](https://github.com/vitlibar)).
* Allow to use multiple zookeeper clusters. [#17070](https://github.com/ClickHouse/ClickHouse/pull/17070) ([fastio](https://github.com/fastio)).
* Implemented `REPLACE TABLE` and `CREATE OR REPLACE TABLE` queries. [#18521](https://github.com/ClickHouse/ClickHouse/pull/18521) ([tavplubix](https://github.com/tavplubix)).
* Implement `UNION DISTINCT` and treat the plain `UNION` clause as `UNION DISTINCT` by default. Add a setting `union_default_mode` that allows to treat it as `UNION ALL` or require explicit mode specification. [#16338](https://github.com/ClickHouse/ClickHouse/pull/16338) ([flynn](https://github.com/ucasFL)).
* Added function `accurateCastOrNull`. This closes [#10290](https://github.com/ClickHouse/ClickHouse/issues/10290). Add type conversions in `x IN (subquery)` expressions. This closes [#10266](https://github.com/ClickHouse/ClickHouse/issues/10266). [#16724](https://github.com/ClickHouse/ClickHouse/pull/16724) ([Maksim Kita](https://github.com/kitaisreal)).
* IP Dictionary supports `IPv4` / `IPv6` types directly. [#17571](https://github.com/ClickHouse/ClickHouse/pull/17571) ([vdimir](https://github.com/vdimir)).
* IP Dictionary supports key fetching. Resolves [#18241](https://github.com/ClickHouse/ClickHouse/issues/18241). [#18480](https://github.com/ClickHouse/ClickHouse/pull/18480) ([vdimir](https://github.com/vdimir)).
* Add `*.zst` compression/decompression support for data import and export. It enables using `*.zst` in `file()` function and `Content-encoding: zstd` in HTTP client. This closes [#16791 ](https://github.com/ClickHouse/ClickHouse/issues/16791). [#17144](https://github.com/ClickHouse/ClickHouse/pull/17144) ([Abi Palagashvili](https://github.com/fibersel)).
* Added `mannWitneyUTest`, `studentTTest` and `welchTTest` aggregate functions. Refactored `rankCorr` a bit. [#16883](https://github.com/ClickHouse/ClickHouse/pull/16883) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Add functions `countMatches`/`countMatchesCaseInsensitive`. [#17459](https://github.com/ClickHouse/ClickHouse/pull/17459) ([Azat Khuzhin](https://github.com/azat)).
* Implement `countSubstrings()`/`countSubstringsCaseInsensitive()`/`countSubstringsCaseInsensitiveUTF8()` (Count the number of substring occurrences). [#17347](https://github.com/ClickHouse/ClickHouse/pull/17347) ([Azat Khuzhin](https://github.com/azat)).
* Add information about used databases, tables and columns in system.query_log. Add `query_kind` and `normalized_query_hash` fields. [#17726](https://github.com/ClickHouse/ClickHouse/pull/17726) ([Amos Bird](https://github.com/amosbird)).
* Add a setting `optimize_on_insert`. When enabled, do the same transformation for INSERTed block of data as if merge was done on this block (e.g. Replacing, Collapsing, Aggregating...). This setting is enabled by default. This can influence Materialized View and MaterializeMySQL behaviour (see detailed description). This closes [#10683](https://github.com/ClickHouse/ClickHouse/issues/10683). [#16954](https://github.com/ClickHouse/ClickHouse/pull/16954) ([Kruglov Pavel](https://github.com/Avogar)).
* Kerberos Authenticaiton for HDFS. [#16621](https://github.com/ClickHouse/ClickHouse/pull/16621) ([Ilya Golshtein](https://github.com/ilejn)).
* Support `SHOW SETTINGS` statement to show parameters in system.settings. `SHOW CHANGED SETTINGS` and `LIKE/ILIKE` clause are also supported. [#18056](https://github.com/ClickHouse/ClickHouse/pull/18056) ([Jianmei Zhang](https://github.com/zhangjmruc)).
* Function `position` now supports `POSITION(needle IN haystack)` synax for SQL compatibility. This closes [#18701](https://github.com/ClickHouse/ClickHouse/issues/18701). ... [#18779](https://github.com/ClickHouse/ClickHouse/pull/18779) ([Jianmei Zhang](https://github.com/zhangjmruc)).
* Now we have a new storage setting `max_partitions_to_read` for tables in the MergeTree family. It limits the max number of partitions that can be accessed in one query. A user setting `force_max_partition_limit` is also added to enforce this constraint. [#18712](https://github.com/ClickHouse/ClickHouse/pull/18712) ([Amos Bird](https://github.com/amosbird)).
* Add `query_id` column to `system.part_log` for inserted parts. Closes [#10097](https://github.com/ClickHouse/ClickHouse/issues/10097). [#18644](https://github.com/ClickHouse/ClickHouse/pull/18644) ([flynn](https://github.com/ucasFL)).
* Allow create table as select with columns specification. Example `CREATE TABLE t1 (x String) ENGINE = Memory AS SELECT 1;`. [#18060](https://github.com/ClickHouse/ClickHouse/pull/18060) ([Maksim Kita](https://github.com/kitaisreal)).
* Added `arrayMin`, `arrayMax`, `arrayAvg` aggregation functions. [#18032](https://github.com/ClickHouse/ClickHouse/pull/18032) ([Maksim Kita](https://github.com/kitaisreal)).
* Implemented `ATTACH TABLE name FROM 'path/to/data/' (col1 Type1, ...` query. It creates new table with provided structure and attaches table data from provided directory in `user_files`. [#17903](https://github.com/ClickHouse/ClickHouse/pull/17903) ([tavplubix](https://github.com/tavplubix)).
* Add mutation support for StorageMemory. This closes [#9117](https://github.com/ClickHouse/ClickHouse/issues/9117). [#15127](https://github.com/ClickHouse/ClickHouse/pull/15127) ([flynn](https://github.com/ucasFL)).
* Support syntax `EXISTS DATABASE name`. [#18458](https://github.com/ClickHouse/ClickHouse/pull/18458) ([Du Chuan](https://github.com/spongedu)).
* Support builtin function `isIPv4String` && `isIPv6String` like [MySQL](https://github.com/ClickHouse/ClickHouse/compare/master...spongedu:support_is_ipv4?expand=1). [#18349](https://github.com/ClickHouse/ClickHouse/pull/18349) ([Du Chuan](https://github.com/spongedu)).
* Add a new setting `insert_distributed_one_random_shard = 1` to allow insertion into multi-sharded distributed table without any distributed key. [#18294](https://github.com/ClickHouse/ClickHouse/pull/18294) ([Amos Bird](https://github.com/amosbird)).
* Add settings `min_compress_block_size` and `max_compress_block_size` to MergeTreeSettings, which have higher priority than the global settings and take effect when they are set. close [13890](https://github.com/ClickHouse/ClickHouse/issues/13890). [#17867](https://github.com/ClickHouse/ClickHouse/pull/17867) ([flynn](https://github.com/ucasFL)).
* Add support for 64bit roaring bitmaps. [#17858](https://github.com/ClickHouse/ClickHouse/pull/17858) ([Andy Yang](https://github.com/andyyzh)).
* Extended `OPTIMIZE ... DEDUPLICATE` syntax to allow explicit (or implicit with asterisk/column transformers) list of columns to check for duplicates on. ... [#17846](https://github.com/ClickHouse/ClickHouse/pull/17846) ([Vasily Nemkov](https://github.com/Enmk)).
* Added functions `toModifiedJulianDay`, `fromModifiedJulianDay`, `toModifiedJulianDayOrNull`, and `fromModifiedJulianDayOrNull`. These functions convert between Proleptic Gregorian calendar date and Modified Julian Day number. [#17750](https://github.com/ClickHouse/ClickHouse/pull/17750) ([PHO](https://github.com/depressed-pho)).
* Add ability to use custom TLD list: added functions `firstSignificantSubdomainCustom`, `cutToFirstSignificantSubdomainCustom`. [#17748](https://github.com/ClickHouse/ClickHouse/pull/17748) ([Azat Khuzhin](https://github.com/azat)).
* Add support for `PROXYv1` protocol to wrap native TCP interface. Allow quotas to be keyed by proxy-forwarded IP address (applied for `PROXYv1` address and for `X-Forwarded-For` from HTTP interface). This is useful when you provide access to ClickHouse only via trusted proxy (e.g. CloudFlare) but want to account user resources by their original IP addresses. This fixes [#17268](https://github.com/ClickHouse/ClickHouse/issues/17268). [#17707](https://github.com/ClickHouse/ClickHouse/pull/17707) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Now clickhouse-client supports opening `EDITOR` to edit commands. `Alt-Shift-E`. [#17665](https://github.com/ClickHouse/ClickHouse/pull/17665) ([Amos Bird](https://github.com/amosbird)).
* Add function `encodeXMLComponent` to escape characters to place string into XML text node or attribute. [#17659](https://github.com/ClickHouse/ClickHouse/pull/17659) ([nauta](https://github.com/nautaa)).
* Introduce `DETACH TABLE/VIEW ... PERMANENTLY` syntax, so that after restarting the table does not reappear back automatically on restart (only by explicit request). The table can still be attached back using the short syntax ATTACH TABLE. Implements [#5555](https://github.com/ClickHouse/ClickHouse/issues/5555). Fixes [#13850](https://github.com/ClickHouse/ClickHouse/issues/13850). [#17642](https://github.com/ClickHouse/ClickHouse/pull/17642) ([filimonov](https://github.com/filimonov)).
* Add asynchronous metrics on total amount of rows, bytes and parts in MergeTree tables. This fix [#11714](https://github.com/ClickHouse/ClickHouse/issues/11714). [#17639](https://github.com/ClickHouse/ClickHouse/pull/17639) ([flynn](https://github.com/ucasFL)).
* Add settings `limit` and `offset` for out-of-SQL pagination: [#16176](https://github.com/ClickHouse/ClickHouse/issues/16176) They are useful for building APIs. These two settings will affect SELECT query as if it is added like `select * from (your_original_select_query) t limit xxx offset xxx;`. [#17633](https://github.com/ClickHouse/ClickHouse/pull/17633) ([hexiaoting](https://github.com/hexiaoting)).
* Provide a new aggregator combinator : `-SimpleState` to build `SimpleAggregateFunction` types via query. It's useful for defining MaterializedView of AggregatingMergeTree engine, and will benefit projections too. [#16853](https://github.com/ClickHouse/ClickHouse/pull/16853) ([Amos Bird](https://github.com/amosbird)).
* Added `queries-file` parameter for `clickhouse-client` and `clickhouse-local`. [#15930](https://github.com/ClickHouse/ClickHouse/pull/15930) ([Maksim Kita](https://github.com/kitaisreal)).
* Added `query` parameter for `clickhouse-benchmark`. [#17832](https://github.com/ClickHouse/ClickHouse/pull/17832) ([Maksim Kita](https://github.com/kitaisreal)).
* `EXPLAIN AST` now support queries other then `SELECT`. [#18136](https://github.com/ClickHouse/ClickHouse/pull/18136) ([taiyang-li](https://github.com/taiyang-li)).


#### Experimental Feature

* Added functions for calculation of minHash and simHash of text n-grams and shingles. They are intended for semi-duplicate search. Also functions `bitHammingDistance` and `tupleHammingDistance` are added. [#7649](https://github.com/ClickHouse/ClickHouse/pull/7649) ([flynn](https://github.com/ucasFL)).
* Add new data type `Map`. See [#1841](https://github.com/ClickHouse/ClickHouse/issues/1841). First version for Map only supports `String` type of key and value. [#15806](https://github.com/ClickHouse/ClickHouse/pull/15806) ([hexiaoting](https://github.com/hexiaoting)).
* Implement alternative SQL parser based on ANTLR4 runtime and generated from EBNF grammar. [#11298](https://github.com/ClickHouse/ClickHouse/pull/11298) ([Ivan](https://github.com/abyss7)).


#### Performance Improvement

* New IP Dictionary implementation with lower memory consumption, improved performance for some cases, and fixed bugs. [#16804](https://github.com/ClickHouse/ClickHouse/pull/16804) ([vdimir](https://github.com/vdimir)).
* Parallel formatting for data export. [#11617](https://github.com/ClickHouse/ClickHouse/pull/11617) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* LDAP integration: Added `verification_cooldown` parameter in LDAP server connection configuration to allow caching of successful "bind" attempts for configurable period of time. [#15988](https://github.com/ClickHouse/ClickHouse/pull/15988) ([Denis Glazachev](https://github.com/traceon)).
* Add `--no-system-table` option for `clickhouse-local` to run without system tables. This avoids initialization of `DateLUT` that may take noticeable amount of time (tens of milliseconds) at startup. [#18899](https://github.com/ClickHouse/ClickHouse/pull/18899) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Replace `PODArray` with `PODArrayWithStackMemory` in `AggregateFunctionWindowFunnelData` to improve `windowFunnel` function performance. [#18817](https://github.com/ClickHouse/ClickHouse/pull/18817) ([flynn](https://github.com/ucasFL)).
* Don't send empty blocks to shards on synchronous INSERT into Distributed table. This closes [#14571](https://github.com/ClickHouse/ClickHouse/issues/14571). [#18775](https://github.com/ClickHouse/ClickHouse/pull/18775) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Optimized read for StorageMemory. [#18052](https://github.com/ClickHouse/ClickHouse/pull/18052) ([Maksim Kita](https://github.com/kitaisreal)).
* Using Dragonbox algorithm for float to string conversion instead of ryu. This improves performance of float to string conversion significantly. [#17831](https://github.com/ClickHouse/ClickHouse/pull/17831) ([Maksim Kita](https://github.com/kitaisreal)).
* Speedup `IPv6CIDRToRange` implementation. [#17569](https://github.com/ClickHouse/ClickHouse/pull/17569) ([vdimir](https://github.com/vdimir)).
* Add `remerge_sort_lowered_memory_bytes_ratio` setting (If memory usage after remerge does not reduced by this ratio, remerge will be disabled). [#17539](https://github.com/ClickHouse/ClickHouse/pull/17539) ([Azat Khuzhin](https://github.com/azat)).
* Improve performance of AggregatingMergeTree with SimpleAggregateFunction(String) in PK. [#17109](https://github.com/ClickHouse/ClickHouse/pull/17109) ([Azat Khuzhin](https://github.com/azat)).
* Now the `-If` combinator is devirtualized, and `count` is properly vectorized. It is for [this PR](https://github.com/ClickHouse/ClickHouse/pull/17041). [#17043](https://github.com/ClickHouse/ClickHouse/pull/17043) ([Amos Bird](https://github.com/amosbird)).
* Fix performance of reading from `Merge` tables over huge number of `MergeTree` tables. Fixes [#7748](https://github.com/ClickHouse/ClickHouse/issues/7748). [#16988](https://github.com/ClickHouse/ClickHouse/pull/16988) ([Anton Popov](https://github.com/CurtizJ)).
* Improved performance of function `repeat`. [#16937](https://github.com/ClickHouse/ClickHouse/pull/16937) ([satanson](https://github.com/satanson)).
* Slightly improved performance of float parsing. [#16809](https://github.com/ClickHouse/ClickHouse/pull/16809) ([Maksim Kita](https://github.com/kitaisreal)).
* Add possibility to skip merged partitions for `OPTIMIZE TABLE ... FINAL`. [#15939](https://github.com/ClickHouse/ClickHouse/pull/15939) ([Kruglov Pavel](https://github.com/Avogar)).
* Integrate with [fast_float from Daniel Lemire](https://github.com/lemire/fast_float) to parse floating point numbers. [#16787](https://github.com/ClickHouse/ClickHouse/pull/16787) ([Maksim Kita](https://github.com/kitaisreal)). It is not enabled, because performance its performance is still lower than rough float parser in ClickHouse.
* Fix max_distributed_connections (affects `prefer_localhost_replica = 1` and `max_threads != max_distributed_connections`). [#17848](https://github.com/ClickHouse/ClickHouse/pull/17848) ([Azat Khuzhin](https://github.com/azat)).
* Adaptive choice of single/multi part upload when sending data to S3. Single part upload is controlled by a new setting `max_single_part_upload_size`. [#17934](https://github.com/ClickHouse/ClickHouse/pull/17934) ([Pavel Kovalenko](https://github.com/Jokser)).
* Support for async tasks in `PipelineExecutor`. Initial support of async sockets for remote queries. [#17868](https://github.com/ClickHouse/ClickHouse/pull/17868) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Allow to use `optimize_move_to_prewhere` optimization with compact parts, when sizes of columns are unknown. [#17330](https://github.com/ClickHouse/ClickHouse/pull/17330) ([Anton Popov](https://github.com/CurtizJ)).


#### Improvement

* Avoid deadlock when executing INSERT SELECT into itself from a table with `TinyLog` or `Log` table engines. This closes [#6802](https://github.com/ClickHouse/ClickHouse/issues/6802). This closes [#18691](https://github.com/ClickHouse/ClickHouse/issues/18691). This closes [#16812](https://github.com/ClickHouse/ClickHouse/issues/16812). This closes [#14570](https://github.com/ClickHouse/ClickHouse/issues/14570). [#15260](https://github.com/ClickHouse/ClickHouse/pull/15260) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Support `SHOW CREATE VIEW name` syntax like [MySQL](https://dev.mysql.com/doc/refman/5.7/en/show-create-view.html). [#18095](https://github.com/ClickHouse/ClickHouse/pull/18095) ([Du Chuan](https://github.com/spongedu)).
* All queries of type `Decimal * Float` or vice versa are allowed, including aggregate ones (e.g. `SELECT sum(decimal_field * 1.1)` or `SELECT dec_col * float_col`), the result type is Float32 or Float64. [#18145](https://github.com/ClickHouse/ClickHouse/pull/18145) ([Mike](https://github.com/myrrc)).
* Improved minimal Web UI: add history; add sharing support; avoid race condition of different requests; add request in-flight and ready indicators; add favicon; detect Ctrl+Enter if textarea is not in focus. [#17293](https://github.com/ClickHouse/ClickHouse/pull/17293) [#17770](https://github.com/ClickHouse/ClickHouse/pull/17770) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* clickhouse-server didn't send `close` request to ZooKeeper server. [#16837](https://github.com/ClickHouse/ClickHouse/pull/16837) ([alesapin](https://github.com/alesapin)).
* Avoid server abnormal termination in case of too low memory limits (`max_memory_usage = 1` / `max_untracked_memory = 1`). [#17453](https://github.com/ClickHouse/ClickHouse/pull/17453) ([Azat Khuzhin](https://github.com/azat)).
* Fix non-deterministic result of `windowFunnel` function in case of same timestamp for different events. [#18884](https://github.com/ClickHouse/ClickHouse/pull/18884) ([Fuwang Hu](https://github.com/fuwhu)).
* Docker: Explicitly set uid / gid of clickhouse user & group to the fixed values (101) in clickhouse-server Docker images. [#19096](https://github.com/ClickHouse/ClickHouse/pull/19096) ([filimonov](https://github.com/filimonov)).
* Asynchronous INSERTs to `Distributed` tables: Two new settings (by analogy with MergeTree family) has been added: - `fsync_after_insert` - Do fsync for every inserted. Will decreases performance of inserts. - `fsync_directories` - Do fsync for temporary directory (that is used for async INSERT only) after all operations (writes, renames, etc.). [#18864](https://github.com/ClickHouse/ClickHouse/pull/18864) ([Azat Khuzhin](https://github.com/azat)).
* `SYSTEM KILL` command started to work in Docker. This closes [#18847](https://github.com/ClickHouse/ClickHouse/issues/18847). [#18848](https://github.com/ClickHouse/ClickHouse/pull/18848) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Expand macros in the zk path when executing `FETCH PARTITION`. [#18839](https://github.com/ClickHouse/ClickHouse/pull/18839) ([fastio](https://github.com/fastio)).
* Apply `ALTER TABLE <replicated_table> ON CLUSTER MODIFY SETTING ...` to all replicas. Because we don't replicate such alter commands. [#18789](https://github.com/ClickHouse/ClickHouse/pull/18789) ([Amos Bird](https://github.com/amosbird)).
* Allow column transformer `EXCEPT` to accept a string as regular expression matcher. This resolves [#18685](https://github.com/ClickHouse/ClickHouse/issues/18685) . [#18699](https://github.com/ClickHouse/ClickHouse/pull/18699) ([Amos Bird](https://github.com/amosbird)).
* Fix SimpleAggregateFunction in SummingMergeTree. Now it works like AggregateFunction. In previous versions values were summed together regardless to the aggregate function. This fixes [#18564](https://github.com/ClickHouse/ClickHouse/issues/18564) . [#8052](https://github.com/ClickHouse/ClickHouse/issues/8052). [#18637](https://github.com/ClickHouse/ClickHouse/pull/18637) ([Amos Bird](https://github.com/amosbird)). Another fix of using `SimpleAggregateFunction` in `SummingMergeTree`. This fixes [#18676](https://github.com/ClickHouse/ClickHouse/issues/18676) . [#18677](https://github.com/ClickHouse/ClickHouse/pull/18677) ([Amos Bird](https://github.com/amosbird)).
* Fixed assertion error inside allocator in case when last argument of function bar is NaN. Now simple ClickHouse's exception is being thrown. This fixes [#17876](https://github.com/ClickHouse/ClickHouse/issues/17876). [#18520](https://github.com/ClickHouse/ClickHouse/pull/18520) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Fix usability issue: no newline after exception message in some tools. [#18444](https://github.com/ClickHouse/ClickHouse/pull/18444) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Add ability to modify primary and partition key column type from `LowCardinality(Type)` to `Type` and vice versa. Also add an ability to modify primary key column type from `EnumX ` to `IntX` type. Fixes [#5604](https://github.com/ClickHouse/ClickHouse/issues/5604). [#18362](https://github.com/ClickHouse/ClickHouse/pull/18362) ([alesapin](https://github.com/alesapin)).
* Implement `untuple` field access. [#18133](https://github.com/ClickHouse/ClickHouse/issues/18133). [#18309](https://github.com/ClickHouse/ClickHouse/pull/18309) ([hexiaoting](https://github.com/hexiaoting)).
* Allow to parse Array fields from CSV if it is represented as a string containing array that was serialized as nested CSV. Example: `"[""Hello"", ""world"", ""42"""" TV""]"` will parse as `['Hello', 'world', '42" TV']`. Allow to parse array in CSV in a string without enclosing braces. Example: `"'Hello', 'world', '42"" TV'"` will parse as `['Hello', 'world', '42" TV']`. [#18271](https://github.com/ClickHouse/ClickHouse/pull/18271) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Make better adaptive granularity calculation for merge tree wide parts. [#18223](https://github.com/ClickHouse/ClickHouse/pull/18223) ([alesapin](https://github.com/alesapin)).
* Now `clickhouse install` could work on Mac. The problem was that there is no procfs on this platform. [#18201](https://github.com/ClickHouse/ClickHouse/pull/18201) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Better hints for `SHOW ...` query syntax. [#18183](https://github.com/ClickHouse/ClickHouse/pull/18183) ([Du Chuan](https://github.com/spongedu)).
* Array aggregation `arrayMin`, `arrayMax`, `arraySum`, `arrayAvg` support for `Int128`, `Int256`, `UInt256`. [#18147](https://github.com/ClickHouse/ClickHouse/pull/18147) ([Maksim Kita](https://github.com/kitaisreal)).
* Add `disk` to Set and Join storage settings. [#18112](https://github.com/ClickHouse/ClickHouse/pull/18112) ([Grigory Pervakov](https://github.com/GrigoryPervakov)).
* Access control: Now table function `merge()` requires current user to have `SELECT` privilege on each table it receives data from. This PR fixes [#16964](https://github.com/ClickHouse/ClickHouse/issues/16964). [#18104](https://github.com/ClickHouse/ClickHouse/pull/18104) [#17983](https://github.com/ClickHouse/ClickHouse/pull/17983) ([Vitaly Baranov](https://github.com/vitlibar)).
* Temporary tables are visible in the system tables `system.tables` and `system.columns` now only in those session where they have been created. The internal database `_temporary_and_external_tables` is now hidden in those system tables; temporary tables are shown as tables with empty database with the `is_temporary` flag set instead. [#18014](https://github.com/ClickHouse/ClickHouse/pull/18014) ([Vitaly Baranov](https://github.com/vitlibar)).
* Fix clickhouse-client rendering issue when the size of terminal window changes. [#18009](https://github.com/ClickHouse/ClickHouse/pull/18009) ([Amos Bird](https://github.com/amosbird)).
* Decrease log verbosity of the events when the client drops the connection from Warning to Information. [#18005](https://github.com/ClickHouse/ClickHouse/pull/18005) ([filimonov](https://github.com/filimonov)).
* Forcibly removing empty or bad metadata files from filesystem for DiskS3. S3 is an experimental feature. [#17935](https://github.com/ClickHouse/ClickHouse/pull/17935) ([Pavel Kovalenko](https://github.com/Jokser)).
* Access control: `allow_introspection_functions=0` prohibits usage of introspection functions but doesn't prohibit giving grants for them anymore (the grantee will need to set `allow_introspection_functions=1` for himself to be able to use that grant). Similarly `allow_ddl=0` prohibits usage of DDL commands but doesn't prohibit giving grants for them anymore. [#17908](https://github.com/ClickHouse/ClickHouse/pull/17908) ([Vitaly Baranov](https://github.com/vitlibar)).
* Usability improvement: hints for column names. [#17112](https://github.com/ClickHouse/ClickHouse/issues/17112). [#17857](https://github.com/ClickHouse/ClickHouse/pull/17857) ([fastio](https://github.com/fastio)).
* Add diagnostic information when two merge tables try to read each other's data. [#17854](https://github.com/ClickHouse/ClickHouse/pull/17854) ([徐炘](https://github.com/weeds085490)).
* Let the possibility to override timeout value for running script using the ClickHouse docker image. [#17818](https://github.com/ClickHouse/ClickHouse/pull/17818) ([Guillaume Tassery](https://github.com/YiuRULE)).
* Check system log tables' engine definition grammar to prevent some configuration errors. Notes that this grammar check is not semantical, that means such mistakes as non-existent columns / expression functions would be not found out util the table is created. [#17739](https://github.com/ClickHouse/ClickHouse/pull/17739) ([Du Chuan](https://github.com/spongedu)).
* Removed exception throwing at `RabbitMQ` table initialization if there was no connection (it will be reconnecting in the background). [#17709](https://github.com/ClickHouse/ClickHouse/pull/17709) ([Kseniia Sumarokova](https://github.com/kssenii)).
* Do not ignore server memory limits during Buffer flush. [#17646](https://github.com/ClickHouse/ClickHouse/pull/17646) ([Azat Khuzhin](https://github.com/azat)).
* Switch to patched version of RocksDB (from ClickHouse-Extras) to fix use-after-free error. [#17643](https://github.com/ClickHouse/ClickHouse/pull/17643) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Added an offset to exception message for parallel parsing. This fixes [#17457](https://github.com/ClickHouse/ClickHouse/issues/17457). [#17641](https://github.com/ClickHouse/ClickHouse/pull/17641) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Don't throw "Too many parts" error in the middle of INSERT query. [#17566](https://github.com/ClickHouse/ClickHouse/pull/17566) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Allow query parameters in UPDATE statement of ALTER query. Fixes [#10976](https://github.com/ClickHouse/ClickHouse/issues/10976). [#17563](https://github.com/ClickHouse/ClickHouse/pull/17563) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Query obfuscator: avoid usage of some SQL keywords for identifier names. [#17526](https://github.com/ClickHouse/ClickHouse/pull/17526) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Export current max ddl entry executed by DDLWorker via server metric. It's useful to check if DDLWorker hangs somewhere. [#17464](https://github.com/ClickHouse/ClickHouse/pull/17464) ([Amos Bird](https://github.com/amosbird)).
* Export asynchronous metrics of all servers current threads. It's useful to track down issues like [this](https://github.com/ClickHouse-Extras/poco/pull/28). [#17463](https://github.com/ClickHouse/ClickHouse/pull/17463) ([Amos Bird](https://github.com/amosbird)).
* Include dynamic columns like MATERIALIZED / ALIAS for wildcard query when settings `asterisk_include_materialized_columns` and `asterisk_include_alias_columns` are turned on. [#17462](https://github.com/ClickHouse/ClickHouse/pull/17462) ([Ken Chen](https://github.com/chenziliang)).
* Allow specifying [TTL](https://clickhouse.tech/docs/en/engines/table-engines/mergetree-family/mergetree/#mergetree-table-ttl) to remove old entries from [system log tables](https://clickhouse.tech/docs/en/operations/system-tables/), using the `<ttl>` attribute in `config.xml`. [#17438](https://github.com/ClickHouse/ClickHouse/pull/17438) ([Du Chuan](https://github.com/spongedu)).
* Now queries coming to the server via MySQL and PostgreSQL protocols have distinctive interface types (which can be seen in the `interface` column of the table`system.query_log`): `4` for MySQL, and `5` for PostgreSQL, instead of formerly used `1` which is now used for the native protocol only. [#17437](https://github.com/ClickHouse/ClickHouse/pull/17437) ([Vitaly Baranov](https://github.com/vitlibar)).
* Fix parsing of SETTINGS clause of the `INSERT ... SELECT ... SETTINGS` query. [#17414](https://github.com/ClickHouse/ClickHouse/pull/17414) ([Azat Khuzhin](https://github.com/azat)).
* Correctly account memory in RadixSort. [#17412](https://github.com/ClickHouse/ClickHouse/pull/17412) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Add eof check in `receiveHello` in server to prevent getting `Attempt to read after eof` exception. [#17365](https://github.com/ClickHouse/ClickHouse/pull/17365) ([Kruglov Pavel](https://github.com/Avogar)).
* Avoid possible stack overflow in bigint conversion. Big integers are experimental. [#17269](https://github.com/ClickHouse/ClickHouse/pull/17269) ([flynn](https://github.com/ucasFL)).
* Now `set` indices will work with `GLOBAL IN`. This fixes [#17232](https://github.com/ClickHouse/ClickHouse/issues/17232) , [#5576](https://github.com/ClickHouse/ClickHouse/issues/5576) . [#17253](https://github.com/ClickHouse/ClickHouse/pull/17253) ([Amos Bird](https://github.com/amosbird)).
* Add limit for http redirects in request to S3 storage (`s3_max_redirects`). [#17220](https://github.com/ClickHouse/ClickHouse/pull/17220) ([ianton-ru](https://github.com/ianton-ru)).
* When `-OrNull` combinator combined `-If`, `-Merge`, `-MergeState`, `-State` combinators, we should put `-OrNull` in front. [#16935](https://github.com/ClickHouse/ClickHouse/pull/16935) ([flynn](https://github.com/ucasFL)).
* Support HTTP proxy and HTTPS S3 endpoint configuration. [#16861](https://github.com/ClickHouse/ClickHouse/pull/16861) ([Pavel Kovalenko](https://github.com/Jokser)).
* Added proper authentication using environment, `~/.aws` and `AssumeRole` for S3 client. [#16856](https://github.com/ClickHouse/ClickHouse/pull/16856) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Add more OpenTelemetry spans. Add an example of how to export the span data to Zipkin. [#16535](https://github.com/ClickHouse/ClickHouse/pull/16535) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Cache dictionaries: Completely eliminate callbacks and locks for acquiring them. Keys are not divided into "not found" and "expired", but stored in the same map during query. [#14958](https://github.com/ClickHouse/ClickHouse/pull/14958) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Fix never worked `fsync_part_directory`/`fsync_after_insert`/`in_memory_parts_insert_sync` (experimental feature). [#18845](https://github.com/ClickHouse/ClickHouse/pull/18845) ([Azat Khuzhin](https://github.com/azat)).
* Allow using `Atomic` engine for nested database of `MaterializeMySQL` engine. [#14849](https://github.com/ClickHouse/ClickHouse/pull/14849) ([tavplubix](https://github.com/tavplubix)).


#### Bug Fix

* Fix the issue when server can stop accepting connections in very rare cases. [#17542](https://github.com/ClickHouse/ClickHouse/pull/17542) (Amos Bird, [alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix index analysis of binary functions with constant argument which leads to wrong query results. This fixes [#18364](https://github.com/ClickHouse/ClickHouse/issues/18364). [#18373](https://github.com/ClickHouse/ClickHouse/pull/18373) ([Amos Bird](https://github.com/amosbird)).
* Fix possible wrong index analysis when the types of the index comparison are different. This fixes [#17122](https://github.com/ClickHouse/ClickHouse/issues/17122). [#17145](https://github.com/ClickHouse/ClickHouse/pull/17145) ([Amos Bird](https://github.com/amosbird)).
* Disable write with AIO during merges because it can lead to extremely rare data corruption of primary key columns during merge. [#18481](https://github.com/ClickHouse/ClickHouse/pull/18481) ([alesapin](https://github.com/alesapin)).
* Restrict merges from wide to compact parts. In case of vertical merge it led to broken result part. [#18381](https://github.com/ClickHouse/ClickHouse/pull/18381) ([Anton Popov](https://github.com/CurtizJ)).
* Fix possible incomplete query result while reading from `MergeTree*` in case of read backoff (message `<Debug> MergeTreeReadPool: Will lower number of threads` in logs). Was introduced in [#16423](https://github.com/ClickHouse/ClickHouse/issues/16423). Fixes [#18137](https://github.com/ClickHouse/ClickHouse/issues/18137). [#18216](https://github.com/ClickHouse/ClickHouse/pull/18216) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix use after free bug in `rocksdb` library. [#18862](https://github.com/ClickHouse/ClickHouse/pull/18862) ([sundyli](https://github.com/sundy-li)).
* Fix infinite reading from file in `ORC` format (was introduced in [#10580](https://github.com/ClickHouse/ClickHouse/issues/10580)). Fixes [#19095](https://github.com/ClickHouse/ClickHouse/issues/19095). [#19134](https://github.com/ClickHouse/ClickHouse/pull/19134) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix bug in merge tree data writer which can lead to marks with bigger size than fixed granularity size. Fixes [#18913](https://github.com/ClickHouse/ClickHouse/issues/18913). [#19123](https://github.com/ClickHouse/ClickHouse/pull/19123) ([alesapin](https://github.com/alesapin)).
* Fix startup bug when clickhouse was not able to read compression codec from `LowCardinality(Nullable(...))` and throws exception `Attempt to read after EOF`. Fixes [#18340](https://github.com/ClickHouse/ClickHouse/issues/18340). [#19101](https://github.com/ClickHouse/ClickHouse/pull/19101) ([alesapin](https://github.com/alesapin)).
* Restrict `MODIFY TTL` queries for `MergeTree` tables created in old syntax. Previously the query succeeded, but actually it had no effect. [#19064](https://github.com/ClickHouse/ClickHouse/pull/19064) ([Anton Popov](https://github.com/CurtizJ)).
* Make sure `groupUniqArray` returns correct type for argument of Enum type. This closes [#17875](https://github.com/ClickHouse/ClickHouse/issues/17875). [#19019](https://github.com/ClickHouse/ClickHouse/pull/19019) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix possible error `Expected single dictionary argument for function` if use function `ignore` with `LowCardinality` argument. Fixes [#14275](https://github.com/ClickHouse/ClickHouse/issues/14275). [#19016](https://github.com/ClickHouse/ClickHouse/pull/19016) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix inserting of `LowCardinality` column to table with `TinyLog` engine. Fixes [#18629](https://github.com/ClickHouse/ClickHouse/issues/18629). [#19010](https://github.com/ClickHouse/ClickHouse/pull/19010) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Join tries to materialize const columns, but our code wants them in other places. [#18982](https://github.com/ClickHouse/ClickHouse/pull/18982) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Disable `optimize_move_functions_out_of_any` because optimization is not always correct. This closes [#18051](https://github.com/ClickHouse/ClickHouse/issues/18051). This closes [#18973](https://github.com/ClickHouse/ClickHouse/issues/18973). [#18981](https://github.com/ClickHouse/ClickHouse/pull/18981) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix possible exception `QueryPipeline stream: different number of columns` caused by merging of query plan's `Expression` steps. Fixes [#18190](https://github.com/ClickHouse/ClickHouse/issues/18190). [#18980](https://github.com/ClickHouse/ClickHouse/pull/18980) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fixed very rare deadlock at shutdown. [#18977](https://github.com/ClickHouse/ClickHouse/pull/18977) ([tavplubix](https://github.com/tavplubix)).
* Fix incorrect behavior when `ALTER TABLE ... DROP PART 'part_name'` query removes all deduplication blocks for the whole partition. Fixes [#18874](https://github.com/ClickHouse/ClickHouse/issues/18874). [#18969](https://github.com/ClickHouse/ClickHouse/pull/18969) ([alesapin](https://github.com/alesapin)).
* Attach partition should reset the mutation. [#18804](https://github.com/ClickHouse/ClickHouse/issues/18804). [#18935](https://github.com/ClickHouse/ClickHouse/pull/18935) ([fastio](https://github.com/fastio)).
* Fix issue with `bitmapOrCardinality` that may lead to nullptr dereference. This closes [#18911](https://github.com/ClickHouse/ClickHouse/issues/18911). [#18912](https://github.com/ClickHouse/ClickHouse/pull/18912) ([sundyli](https://github.com/sundy-li)).
* Fix possible hang at shutdown in `clickhouse-local`. This fixes [#18891](https://github.com/ClickHouse/ClickHouse/issues/18891). [#18893](https://github.com/ClickHouse/ClickHouse/pull/18893) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Queries for external databases (MySQL, ODBC, JDBC) were incorrectly rewritten if there was an expression in form of `x IN table`. This fixes [#9756](https://github.com/ClickHouse/ClickHouse/issues/9756). [#18876](https://github.com/ClickHouse/ClickHouse/pull/18876) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix *If combinator with unary function and Nullable types. [#18806](https://github.com/ClickHouse/ClickHouse/pull/18806) ([Azat Khuzhin](https://github.com/azat)).
* Fix the issue that asynchronous distributed INSERTs can be rejected by the server if the setting `network_compression_method` is globally set to non-default value. This fixes [#18741](https://github.com/ClickHouse/ClickHouse/issues/18741). [#18776](https://github.com/ClickHouse/ClickHouse/pull/18776) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fixed `Attempt to read after eof` error when trying to `CAST` `NULL` from `Nullable(String)` to `Nullable(Decimal(P, S))`. Now function `CAST` returns `NULL` when it cannot parse decimal from nullable string. Fixes [#7690](https://github.com/ClickHouse/ClickHouse/issues/7690). [#18718](https://github.com/ClickHouse/ClickHouse/pull/18718) ([Winter Zhang](https://github.com/zhang2014)).
* Fix minor issue with logging. [#18717](https://github.com/ClickHouse/ClickHouse/pull/18717) ([sundyli](https://github.com/sundy-li)).
* Fix removing of empty parts in `ReplicatedMergeTree` tables, created with old syntax. Fixes [#18582](https://github.com/ClickHouse/ClickHouse/issues/18582). [#18614](https://github.com/ClickHouse/ClickHouse/pull/18614) ([Anton Popov](https://github.com/CurtizJ)).
* Fix previous bug when date overflow with different values. Strict Date value limit to "2106-02-07", cast date > "2106-02-07" to value 0. [#18565](https://github.com/ClickHouse/ClickHouse/pull/18565) ([hexiaoting](https://github.com/hexiaoting)).
* Add FixedString data type support for replication from MySQL. Replication from MySQL is an experimental feature. This patch fixes [#18450](https://github.com/ClickHouse/ClickHouse/issues/18450) Also fixes [#6556](https://github.com/ClickHouse/ClickHouse/issues/6556). [#18553](https://github.com/ClickHouse/ClickHouse/pull/18553) ([awesomeleo](https://github.com/awesomeleo)).
* Fix possible `Pipeline stuck` error while using `ORDER BY` after subquery with `RIGHT` or `FULL` join. [#18550](https://github.com/ClickHouse/ClickHouse/pull/18550) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fix bug which may lead to `ALTER` queries hung after corresponding mutation kill. Found by thread fuzzer. [#18518](https://github.com/ClickHouse/ClickHouse/pull/18518) ([alesapin](https://github.com/alesapin)).
* Proper support for 12AM in `parseDateTimeBestEffort` function. This fixes [#18402](https://github.com/ClickHouse/ClickHouse/issues/18402). [#18449](https://github.com/ClickHouse/ClickHouse/pull/18449) ([vladimir-golovchenko](https://github.com/vladimir-golovchenko)).
* Fixed `value is too short` error when executing `toType(...)` functions (`toDate`, `toUInt32`, etc) with argument of type `Nullable(String)`. Now such functions return `NULL` on parsing errors instead of throwing exception. Fixes [#7673](https://github.com/ClickHouse/ClickHouse/issues/7673). [#18445](https://github.com/ClickHouse/ClickHouse/pull/18445) ([tavplubix](https://github.com/tavplubix)).
* Fix the unexpected behaviour of `SHOW TABLES`. [#18431](https://github.com/ClickHouse/ClickHouse/pull/18431) ([fastio](https://github.com/fastio)).
* Fix -SimpleState combinator generates incompatible arugment type and return type. [#18404](https://github.com/ClickHouse/ClickHouse/pull/18404) ([Amos Bird](https://github.com/amosbird)).
* Fix possible race condition in concurrent usage of `Set` or `Join` tables and selects from `system.tables`. [#18385](https://github.com/ClickHouse/ClickHouse/pull/18385) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix filling table `system.settings_profile_elements`. This PR fixes [#18231](https://github.com/ClickHouse/ClickHouse/issues/18231). [#18379](https://github.com/ClickHouse/ClickHouse/pull/18379) ([Vitaly Baranov](https://github.com/vitlibar)).
* Fix possible crashes in aggregate functions with combinator `Distinct`, while using two-level aggregation. Fixes [#17682](https://github.com/ClickHouse/ClickHouse/issues/17682). [#18365](https://github.com/ClickHouse/ClickHouse/pull/18365) ([Anton Popov](https://github.com/CurtizJ)).
* Fixed issue when `clickhouse-odbc-bridge` process is unreachable by server on machines with dual IPv4/IPv6 stack; Fixed issue when ODBC dictionary updates are performed using malformed queries and/or cause crashes of the odbc-bridge process; Possibly closes [#14489](https://github.com/ClickHouse/ClickHouse/issues/14489). [#18278](https://github.com/ClickHouse/ClickHouse/pull/18278) ([Denis Glazachev](https://github.com/traceon)).
* Access control: `SELECT count() FROM table` now can be executed if the user has access to at least single column from a table. This PR fixes [#10639](https://github.com/ClickHouse/ClickHouse/issues/10639). [#18233](https://github.com/ClickHouse/ClickHouse/pull/18233) ([Vitaly Baranov](https://github.com/vitlibar)).
* Access control: `SELECT JOIN` now requires the `SELECT` privilege on each of the joined tables. This PR fixes [#17654](https://github.com/ClickHouse/ClickHouse/issues/17654). [#18232](https://github.com/ClickHouse/ClickHouse/pull/18232) ([Vitaly Baranov](https://github.com/vitlibar)).
* Fix key comparison between Enum and Int types. This fixes [#17989](https://github.com/ClickHouse/ClickHouse/issues/17989). [#18214](https://github.com/ClickHouse/ClickHouse/pull/18214) ([Amos Bird](https://github.com/amosbird)).
* Replication from MySQL (experimental feature). Fixes [#18186](https://github.com/ClickHouse/ClickHouse/issues/18186) Fixes [#16372](https://github.com/ClickHouse/ClickHouse/issues/16372) Fix unique key convert issue in MaterializeMySQL database engine. [#18211](https://github.com/ClickHouse/ClickHouse/pull/18211) ([Winter Zhang](https://github.com/zhang2014)).
* Fix inconsistency for queries with both `WITH FILL` and `WITH TIES` [#17466](https://github.com/ClickHouse/ClickHouse/issues/17466). [#18188](https://github.com/ClickHouse/ClickHouse/pull/18188) ([hexiaoting](https://github.com/hexiaoting)).
* Fix inserting a row with default value in case of parsing error in the last column. Fixes [#17712](https://github.com/ClickHouse/ClickHouse/issues/17712). [#18182](https://github.com/ClickHouse/ClickHouse/pull/18182) ([Jianmei Zhang](https://github.com/zhangjmruc)).
* Fix `Unknown setting profile` error on attempt to set settings profile. [#18167](https://github.com/ClickHouse/ClickHouse/pull/18167) ([tavplubix](https://github.com/tavplubix)).
* Fix error when query `MODIFY COLUMN ... REMOVE TTL` doesn't actually remove column TTL. [#18130](https://github.com/ClickHouse/ClickHouse/pull/18130) ([alesapin](https://github.com/alesapin)).
* Fixed `std::out_of_range: basic_string` in S3 URL parsing. [#18059](https://github.com/ClickHouse/ClickHouse/pull/18059) ([Vladimir Chebotarev](https://github.com/excitoon)).
* Fix comparison of `DateTime64` and `Date`. Fixes [#13804](https://github.com/ClickHouse/ClickHouse/issues/13804) and [#11222](https://github.com/ClickHouse/ClickHouse/issues/11222). ... [#18050](https://github.com/ClickHouse/ClickHouse/pull/18050) ([Vasily Nemkov](https://github.com/Enmk)).
* Replication from MySQL (experimental feature): Fixes [#15187](https://github.com/ClickHouse/ClickHouse/issues/15187) Fixes [#17912](https://github.com/ClickHouse/ClickHouse/issues/17912) support convert MySQL prefix index for MaterializeMySQL. [#17944](https://github.com/ClickHouse/ClickHouse/pull/17944) ([Winter Zhang](https://github.com/zhang2014)).
* When server log rotation was configured using `logger.size` parameter with numeric value larger than 2^32, the logs were not rotated properly. This is fixed. [#17905](https://github.com/ClickHouse/ClickHouse/pull/17905) ([Alexander Kuzmenkov](https://github.com/akuzm)).
* Trivial query optimization was producing wrong result if query contains ARRAY JOIN (so query is actually non trivial). [#17887](https://github.com/ClickHouse/ClickHouse/pull/17887) ([sundyli](https://github.com/sundy-li)).
* Fix possible segfault in `topK` aggregate function. This closes [#17404](https://github.com/ClickHouse/ClickHouse/issues/17404). [#17845](https://github.com/ClickHouse/ClickHouse/pull/17845) ([Maksim Kita](https://github.com/kitaisreal)).
* WAL (experimental feature): Do not restore parts from WAL if `in_memory_parts_enable_wal` is disabled. [#17802](https://github.com/ClickHouse/ClickHouse/pull/17802) ([detailyang](https://github.com/detailyang)).
* Exception message about max table size to drop was displayed incorrectly. [#17764](https://github.com/ClickHouse/ClickHouse/pull/17764) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fixed possible segfault when there is not enough space when inserting into `Distributed` table. [#17737](https://github.com/ClickHouse/ClickHouse/pull/17737) ([tavplubix](https://github.com/tavplubix)).
* Fixed problem when ClickHouse fails to resume connection to MySQL servers. [#17681](https://github.com/ClickHouse/ClickHouse/pull/17681) ([Alexander Kazakov](https://github.com/Akazz)).
* Windows: Fixed `Function not implemented` error when executing `RENAME` query in `Atomic` database with ClickHouse running on Windows Subsystem for Linux. Fixes [#17661](https://github.com/ClickHouse/ClickHouse/issues/17661). [#17664](https://github.com/ClickHouse/ClickHouse/pull/17664) ([tavplubix](https://github.com/tavplubix)).
* In might be determined incorrectly if cluster is circular- (cross-) replicated or not when executing `ON CLUSTER` query due to race condition when `pool_size` > 1. It's fixed. [#17640](https://github.com/ClickHouse/ClickHouse/pull/17640) ([tavplubix](https://github.com/tavplubix)).
* Fix empty `system.stack_trace` table when server is running in daemon mode. [#17630](https://github.com/ClickHouse/ClickHouse/pull/17630) ([Amos Bird](https://github.com/amosbird)).
* Exception `fmt::v7::format_error` can be logged in background for MergeTree tables. This fixes [#17613](https://github.com/ClickHouse/ClickHouse/issues/17613). [#17615](https://github.com/ClickHouse/ClickHouse/pull/17615) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* When clickhouse-client is used in interactive mode with multiline queries, single line comment was erronously extended till the end of query. This fixes [#13654](https://github.com/ClickHouse/ClickHouse/issues/13654). [#17565](https://github.com/ClickHouse/ClickHouse/pull/17565) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix alter query hang when the corresponding mutation was killed on the different replica. Fixes [#16953](https://github.com/ClickHouse/ClickHouse/issues/16953). [#17499](https://github.com/ClickHouse/ClickHouse/pull/17499) ([alesapin](https://github.com/alesapin)).
* Fix issue with memory accounting when mark cache size was underestimated by clickhouse. It may happen when there are a lot of tiny files with marks. [#17496](https://github.com/ClickHouse/ClickHouse/pull/17496) ([alesapin](https://github.com/alesapin)).
* Fix `ORDER BY` with enabled setting `optimize_redundant_functions_in_order_by`. [#17471](https://github.com/ClickHouse/ClickHouse/pull/17471) ([Anton Popov](https://github.com/CurtizJ)).
* Fix duplicates after `DISTINCT` which were possible because of incorrect optimization. Fixes [#17294](https://github.com/ClickHouse/ClickHouse/issues/17294). [#17296](https://github.com/ClickHouse/ClickHouse/pull/17296) ([li chengxiang](https://github.com/chengxianglibra)). [#17439](https://github.com/ClickHouse/ClickHouse/pull/17439) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Fixed high CPU usage in background tasks of *MergeTree tables. [#17416](https://github.com/ClickHouse/ClickHouse/pull/17416) ([tavplubix](https://github.com/tavplubix)).
* Fix possible crash while reading from `JOIN` table with `LowCardinality` types. Fixes [#17228](https://github.com/ClickHouse/ClickHouse/issues/17228). [#17397](https://github.com/ClickHouse/ClickHouse/pull/17397) ([Nikolai Kochetov](https://github.com/KochetovNicolai)).
* Replication from MySQL (experimental feature): Fixes [#16835](https://github.com/ClickHouse/ClickHouse/issues/16835) try fix miss match header with MySQL SHOW statement. [#17366](https://github.com/ClickHouse/ClickHouse/pull/17366) ([Winter Zhang](https://github.com/zhang2014)).
* Fix nondeterministic functions with predicate optimizer. This fixes [#17244](https://github.com/ClickHouse/ClickHouse/issues/17244). [#17273](https://github.com/ClickHouse/ClickHouse/pull/17273) ([Winter Zhang](https://github.com/zhang2014)).
* Fix possible `Unexpected packet Data received from client` error for Distributed queries with `LIMIT`. [#17254](https://github.com/ClickHouse/ClickHouse/pull/17254) ([Azat Khuzhin](https://github.com/azat)).
* Fix set index invalidation when there are const columns in the subquery. This fixes [#17246](https://github.com/ClickHouse/ClickHouse/issues/17246). [#17249](https://github.com/ClickHouse/ClickHouse/pull/17249) ([Amos Bird](https://github.com/amosbird)).
* clickhouse-copier: Fix for non-partitioned tables [#15235](https://github.com/ClickHouse/ClickHouse/issues/15235). [#17248](https://github.com/ClickHouse/ClickHouse/pull/17248) ([Qi Chen](https://github.com/kaka11chen)).
* Fixed possible not-working mutations for parts stored on S3 disk (experimental feature). [#17227](https://github.com/ClickHouse/ClickHouse/pull/17227) ([Pavel Kovalenko](https://github.com/Jokser)).
* Bug fix for funciton `fuzzBits`, related issue: [#16980](https://github.com/ClickHouse/ClickHouse/issues/16980). [#17051](https://github.com/ClickHouse/ClickHouse/pull/17051) ([hexiaoting](https://github.com/hexiaoting)).
* Fix `optimize_distributed_group_by_sharding_key` for query with OFFSET only. [#16996](https://github.com/ClickHouse/ClickHouse/pull/16996) ([Azat Khuzhin](https://github.com/azat)).
* Fix queries from `Merge` tables over `Distributed` tables with JOINs. [#16993](https://github.com/ClickHouse/ClickHouse/pull/16993) ([Azat Khuzhin](https://github.com/azat)).
* Fix order by optimization with monotonic functions. Fixes [#16107](https://github.com/ClickHouse/ClickHouse/issues/16107). [#16956](https://github.com/ClickHouse/ClickHouse/pull/16956) ([Anton Popov](https://github.com/CurtizJ)).
* Fix incorrect comparison of types `DateTime64` with different scales. Fixes [#16655](https://github.com/ClickHouse/ClickHouse/issues/16655) ... [#16952](https://github.com/ClickHouse/ClickHouse/pull/16952) ([Vasily Nemkov](https://github.com/Enmk)).
* Fix optimization of group by with enabled setting `optimize_aggregators_of_group_by_keys` and joins. Fixes [#12604](https://github.com/ClickHouse/ClickHouse/issues/12604). [#16951](https://github.com/ClickHouse/ClickHouse/pull/16951) ([Anton Popov](https://github.com/CurtizJ)).
* Minor fix in SHOW ACCESS query. [#16866](https://github.com/ClickHouse/ClickHouse/pull/16866) ([tavplubix](https://github.com/tavplubix)).
* Fix the behaviour with enabled `optimize_trivial_count_query` setting with partition predicate. [#16767](https://github.com/ClickHouse/ClickHouse/pull/16767) ([Azat Khuzhin](https://github.com/azat)).
* Return number of affected rows for INSERT queries via MySQL wire protocol. Previously ClickHouse used to always return 0, it's fixed. Fixes [#16605](https://github.com/ClickHouse/ClickHouse/issues/16605). [#16715](https://github.com/ClickHouse/ClickHouse/pull/16715) ([Winter Zhang](https://github.com/zhang2014)).
* Fix inconsistent behavior caused by `select_sequential_consistency` for optimized trivial count query and system tables. [#16309](https://github.com/ClickHouse/ClickHouse/pull/16309) ([Hao Chen](https://github.com/haoch)).
* Throw error when `REPLACE` column transformer operates on non existing column. [#16183](https://github.com/ClickHouse/ClickHouse/pull/16183) ([hexiaoting](https://github.com/hexiaoting)).
* Throw exception in case of not equi-join ON expression in RIGH|FULL JOIN. [#15162](https://github.com/ClickHouse/ClickHouse/pull/15162) ([Artem Zuikov](https://github.com/4ertus2)).


#### Build/Testing/Packaging Improvement

* Add simple integrity check for ClickHouse binary. It allows to detect corruption due to faulty hardware (bit rot on storage media or bit flips in RAM). [#18811](https://github.com/ClickHouse/ClickHouse/pull/18811) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Change `OpenSSL` to `BoringSSL`. It allows to avoid issues with sanitizers. This fixes [#12490](https://github.com/ClickHouse/ClickHouse/issues/12490). This fixes [#17502](https://github.com/ClickHouse/ClickHouse/issues/17502). This fixes [#12952](https://github.com/ClickHouse/ClickHouse/issues/12952). [#18129](https://github.com/ClickHouse/ClickHouse/pull/18129) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Simplify `Sys/V` init script. It was not working on Ubuntu 12.04 or older. [#17428](https://github.com/ClickHouse/ClickHouse/pull/17428) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Multiple improvements in `./clickhouse install` script. [#17421](https://github.com/ClickHouse/ClickHouse/pull/17421) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Now ClickHouse can pretend to be a fake ZooKeeper. Currently, storage implementation is just stored in-memory hash-table, and server partially support ZooKeeper protocol. [#16877](https://github.com/ClickHouse/ClickHouse/pull/16877) ([alesapin](https://github.com/alesapin)).
* Fix dead list watches removal for TestKeeperStorage (a mock for ZooKeeper). [#18065](https://github.com/ClickHouse/ClickHouse/pull/18065) ([alesapin](https://github.com/alesapin)).
* Add `SYSTEM SUSPEND` command for fault injection. It can be used to faciliate failover tests. This closes [#15979](https://github.com/ClickHouse/ClickHouse/issues/15979). [#18850](https://github.com/ClickHouse/ClickHouse/pull/18850) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Generate build id when ClickHouse is linked with `lld`. It's appeared that `lld` does not generate it by default on my machine. Build id is used for crash reports and introspection. [#18808](https://github.com/ClickHouse/ClickHouse/pull/18808) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Fix shellcheck errors in style check. [#18566](https://github.com/ClickHouse/ClickHouse/pull/18566) ([Ilya Yatsishin](https://github.com/qoega)).
* Update timezones info to 2020e. [#18531](https://github.com/ClickHouse/ClickHouse/pull/18531) ([alesapin](https://github.com/alesapin)).
* Fix codespell warnings. Split style checks into separate parts. Update style checks docker image. [#18463](https://github.com/ClickHouse/ClickHouse/pull/18463) ([Ilya Yatsishin](https://github.com/qoega)).
* Automated check for leftovers of conflict markers in docs. [#18332](https://github.com/ClickHouse/ClickHouse/pull/18332) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Enable Thread Fuzzer for stateless tests flaky check. [#18299](https://github.com/ClickHouse/ClickHouse/pull/18299) ([alesapin](https://github.com/alesapin)).
* Do not use non thread-safe function `strerror`. [#18204](https://github.com/ClickHouse/ClickHouse/pull/18204) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Update `anchore/scan-action@main` workflow action (was moved from `master` to `main`). [#18192](https://github.com/ClickHouse/ClickHouse/pull/18192) ([Stig Bakken](https://github.com/stigsb)).
* Now `clickhouse-test` does DROP/CREATE databases with a timeout. [#18098](https://github.com/ClickHouse/ClickHouse/pull/18098) ([alesapin](https://github.com/alesapin)).
* Enable experimental support for Pytest framework for stateless tests. [#17902](https://github.com/ClickHouse/ClickHouse/pull/17902) ([Ivan](https://github.com/abyss7)).
* Now we use the fresh docker daemon version in integration tests. [#17671](https://github.com/ClickHouse/ClickHouse/pull/17671) ([alesapin](https://github.com/alesapin)).
* Send info about official build, memory, cpu and free disk space to Sentry if it is enabled. Sentry is opt-in feature to help ClickHouse developers. This closes [#17279](https://github.com/ClickHouse/ClickHouse/issues/17279). [#17543](https://github.com/ClickHouse/ClickHouse/pull/17543) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* There was an uninitialized variable in the code of clickhouse-copier. [#17363](https://github.com/ClickHouse/ClickHouse/pull/17363) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Fix [one MSan report](https://clickhouse-test-reports.s3.yandex.net/17309/065cd002578f2e8228f12a2744bd40c970065e0c/stress_test_(memory)/stderr.log) from [#17309](https://github.com/ClickHouse/ClickHouse/issues/17309). [#17344](https://github.com/ClickHouse/ClickHouse/pull/17344) ([Nikita Mikhaylov](https://github.com/nikitamikhaylov)).
* Fix for the issue with IPv6 in Arrow Flight library. See [the comments](https://github.com/ClickHouse/ClickHouse/pull/16243#issuecomment-720830294) for details. [#16664](https://github.com/ClickHouse/ClickHouse/pull/16664) ([Zhanna](https://github.com/FawnD2)).
* Add a library that replaces some `libc` functions to traps that will terminate the process. [#16366](https://github.com/ClickHouse/ClickHouse/pull/16366) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Provide diagnostics in server logs in case of stack overflow, send error message to clickhouse-client. This closes [#14840](https://github.com/ClickHouse/ClickHouse/issues/14840). [#16346](https://github.com/ClickHouse/ClickHouse/pull/16346) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Now we can run almost all stateless functional tests in parallel. [#15236](https://github.com/ClickHouse/ClickHouse/pull/15236) ([alesapin](https://github.com/alesapin)).
* Fix corruption in `librdkafka` snappy decompression (was a problem only for gcc10 builds, but official builds uses clang already, so at least recent official releases are not affected). [#18053](https://github.com/ClickHouse/ClickHouse/pull/18053) ([Azat Khuzhin](https://github.com/azat)).
* If server was terminated by OOM killer, print message in log. [#13516](https://github.com/ClickHouse/ClickHouse/pull/13516) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* PODArray: Avoid call to memcpy with (nullptr, 0) arguments (Fix UBSan report). This fixes [#18525](https://github.com/ClickHouse/ClickHouse/issues/18525). [#18526](https://github.com/ClickHouse/ClickHouse/pull/18526) ([alexey-milovidov](https://github.com/alexey-milovidov)).
* Minor improvement for path concatenation of zookeeper paths inside DDLWorker. [#17767](https://github.com/ClickHouse/ClickHouse/pull/17767) ([Bharat Nallan](https://github.com/bharatnc)).
* Allow to reload symbols from debug file. This PR also fixes a build-id issue. [#17637](https://github.com/ClickHouse/ClickHouse/pull/17637) ([Amos Bird](https://github.com/amosbird)).
* TestFlows: fixes to LDAP tests that fail due to slow test execution. [#18790](https://github.com/ClickHouse/ClickHouse/pull/18790) ([vzakaznikov](https://github.com/vzakaznikov)).
* TestFlows: Merging requirements for AES encryption functions. Updating aes_encryption tests to use new requirements. Updating TestFlows version to 1.6.72. [#18221](https://github.com/ClickHouse/ClickHouse/pull/18221) ([vzakaznikov](https://github.com/vzakaznikov)).
* TestFlows: Updating TestFlows version to the latest 1.6.72. Re-generating requirements.py. [#18208](https://github.com/ClickHouse/ClickHouse/pull/18208) ([vzakaznikov](https://github.com/vzakaznikov)).
* TestFlows: Updating TestFlows README.md to include "How To Debug Why Test Failed" section. [#17808](https://github.com/ClickHouse/ClickHouse/pull/17808) ([vzakaznikov](https://github.com/vzakaznikov)).
* TestFlows: tests for RBAC [ACCESS MANAGEMENT](https://clickhouse.tech/docs/en/sql-reference/statements/grant/#grant-access-management) privileges. [#17804](https://github.com/ClickHouse/ClickHouse/pull/17804) ([MyroTk](https://github.com/MyroTk)).
* TestFlows: RBAC tests for SHOW, TRUNCATE, KILL, and OPTIMIZE. - Updates to old tests. - Resolved comments from #https://github.com/ClickHouse/ClickHouse/pull/16977. [#17657](https://github.com/ClickHouse/ClickHouse/pull/17657) ([MyroTk](https://github.com/MyroTk)).
* TestFlows: Added RBAC tests for `ATTACH`, `CREATE`, `DROP`, and `DETACH`. [#16977](https://github.com/ClickHouse/ClickHouse/pull/16977) ([MyroTk](https://github.com/MyroTk)).


## [Changelog for 2020](https://github.com/ClickHouse/ClickHouse/blob/master/docs/en/whats-new/changelog/2020.md)