ClickHouse checks ` min_part_size` and ` min_part_size_ratio` and processes the ` case` blocks that match these conditions. If none of the `<case>` matches, ClickHouse applies the `lz4` compression algorithm.
**Example**
```xml
<compressionincl="clickhouse_compression">
<case>
<min_part_size>10000000000</min_part_size>
<min_part_size_ratio>0.01</min_part_size_ratio>
<method>zstd</method>
</case>
</compression>
```
<aname="server_settings-default_database"></a>
## default_database
The default database.
Use a [ SHOW DATABASES](../query_language/queries.md#query_language_queries_show_databases) query to get a list of databases.
**Example**
```xml
<default_database>default</default_database>
```
<aname="server_settings-default_profile"></a>
## default_profile
Default settings profile.
Settings profiles are located in the file specified in the [user_config](#server_settings-users_config) parameter.
**Example**
```xml
<default_profile>default</default_profile>
```
<aname="server_settings-dictionaries_config"></a>
## dictionaries_config
The path to the config file for external dictionaries.
Path:
- Specify the absolute path or the path relative to the server config file.
- The path can contain wildcards \* and ?.
See also "[External dictionaries](../../dicts/external_dicts.md#dicts-external_dicts)".
If ` true`, then each dictionary is created on first use. If dictionary creation failed, the function that was using the dictionary throws an exception.
If `false`, all dictionaries are created when the server starts, and if there is an error, the server shuts down.
The path to the directory with the schemas for the input data, such as schemas for the [ CapnProto](../../formats/capnproto.md#format_capnproto) format.
**Example**
```xml
<!-- Directory containing schema files for various input formats. -->
- log – The log file. Contains all the entries according to `` level``.
- errorlog – Error log file.
- size – Size of the file. Applies to ``log``and``errorlog``. Once the file reaches ``size``, ClickHouse archives and renames it, and creates a new log file in its place.
- count – The number of archived log files that ClickHouse stores.
For more information, see the section "[Creating replicated tables](../../table_engines/replication.md#table_engines-replication-creation_of_rep_tables)".
**Example**
```xml
<macrosincl="macros"optional="true"/>
```
<aname="server_settings-mark_cache_size"></a>
## mark_cache_size
Approximate size (in bytes) of the cache of "marks" used by [ MergeTree](../../table_engines/mergetree.md#table_engines-mergetree) engines.
The cache is shared for the server and memory is allocated as needed. The cache size must be at least 5368709120.
If the size of a [ MergeTree](../../table_engines/mergetree.md#table_engines-mergetree) type table exceeds `max_table_size_to_drop` (in bytes), you can't delete it using a DROP query.
If you still need to delete the table without restarting the ClickHouse server, create the ` <clickhouse-path>/flags/force_drop_table` file and run the DROP query.
Default value: 50 GB.
The value 0 means that you can delete all tables without any restrictions.
Support for SSL is provided by the `` libpoco`` library. The description of the interface is in the [ SSLManager.h file.](https://github.com/yandex/ClickHouse/blob/master/contrib/libpoco/NetSSL_OpenSSL/include/Poco/Net/SSLManager.h)
Keys for server/client settings:
- privateKeyFile – The path to the file with the secret key of the PEM certificate. The file may contain a key and certificate at the same time.
- certificateFile – The path to the client/server certificate file in PEM format. You can omit it if `` privateKeyFile`` contains the certificate.
- caConfig – The path to the file or directory that contains trusted root certificates.
- verificationMode – The method for checking the node's certificates. Details are in the description of the [Context](https://github.com/yandex/ClickHouse/blob/master/contrib/libpoco/NetSSL_OpenSSL/include/Poco/Net/Context.h) class. Acceptable values: ``none``, ``relaxed``, ``strict``, ``once``.
- verificationDepth – The maximum length of the verification chain. Verification will fail if the certificate chain length exceeds the set value.
- loadDefaultCAFile – Indicates that built-in CA certificates for OpenSSL will be used. Acceptable values: `` true``, `` false``. |
- cacheSessions – Enables or disables caching sessions. Must be used in combination with ``sessionIdContext``. Acceptable values: `` true``, `` false``.
- sessionIdContext – A unique set of random characters that the server appends to each generated identifier. The length of the string must not exceed ``SSL_MAX_SSL_SESSION_ID_LENGTH``. This parameter is always recommended, since it helps avoid problems both if the server caches the session and if the client requested caching. Default value: ``${application.name}``.
- sessionCacheSize – The maximum number of sessions that the server caches. Default value: 1024\*20. 0 – Unlimited sessions.
- sessionTimeout – Time for caching the session on the server.
- extendedVerification – Automatically extended verification of certificates after the session ends. Acceptable values: `` true``, `` false``.
- fips – Activates OpenSSL FIPS mode. Supported if the library's OpenSSL version supports FIPS.
- privateKeyPassphraseHandler – Class (PrivateKeyPassphraseHandler subclass) that requests the passphrase for accessing the private key. For example: ``<privateKeyPassphraseHandler>``, ``<name>KeyFileHandler</name>``, ``<options><password>test</password></options>``, ``</privateKeyPassphraseHandler>``.
- invalidCertificateHandler – Class (subclass of CertificateHandler) for verifying invalid certificates. For example: `` <invalidCertificateHandler><name>ConsoleCertificateHandler</name></invalidCertificateHandler>`` .
- disableProtocols – Protocols that are not allowed to use.
- preferServerCiphers – Preferred server ciphers on the client.
<!-- Use for self-signed: <verificationMode>none</verificationMode> -->
<invalidCertificateHandler>
<!-- Use for self-signed: <name>AcceptCertificateHandler</name> -->
<name>RejectCertificateHandler</name>
</invalidCertificateHandler>
</client>
</openSSL>
```
<aname="server_settings-part_log"></a>
## part_log
Logging events that are associated with the [MergeTree](../../table_engines/mergetree.md#table_engines-mergetree) data type. For instance, adding or merging data. You can use the log to simulate merge algorithms and compare their characteristics. You can visualize the merge process.
Queries are logged in the ClickHouse table, not in a separate file.
Columns in the log:
- event_time – Date of the event.
- duration_ms – Duration of the event.
- event_type – Type of event. 1 – new data part; 2 – merge result; 3 – data part downloaded from replica; 4 – data part deleted.
- database_name – The name of the database.
- table_name – Name of the table.
- part_name – Name of the data part.
- size_in_bytes – Size of the data part in bytes.
- merged_from – An array of names of data parts that make up the merge (also used when downloading a merged part).
- merge_time_ms – Time spent on the merge.
Use the following parameters to configure logging:
- database – Name of the database.
- table – Name of the table.
- flush_interval_milliseconds – Interval for flushing data from memory to the disk.
Queries are logged in the ClickHouse table, not in a separate file.
Use the following parameters to configure logging:
- database – Name of the database.
- table – Name of the table.
- flush_interval_milliseconds – Interval for flushing data from memory to the disk.
If the table doesn't exist, ClickHouse will create it. If the structure of the query log changed when the ClickHouse server was updated, the table with the old structure is renamed, and a new table is created automatically.
Specified as an IANA identifier for the UTC time zone or geographic location (for example, Africa/Abidjan).
The time zone is necessary for conversions between String and DateTime formats when DateTime fields are output to text format (printed on the screen or in a file), and when getting DateTime from a string. In addition, the time zone is used in functions that work with the time and date if they didn't receive the time zone in the input parameters.
**Example**
```xml
<timezone>Europe/Moscow</timezone>
```
<aname="server_settings-tcp_port"></a>
## tcp_port
Port for communicating with clients over the TCP protocol.
**Example**
```xml
<tcp_port>9000</tcp_port>
```
<aname="server_settings-tmp_path"></a>
## tmp_path
Path to temporary data for processing large queries.
Cache size (in bytes) for uncompressed data used by table engines from the [ MergeTree](../../table_engines/mergetree.md#table_engines-mergetree) family.
There is one shared cache for the server. Memory is allocated on demand. The cache is used if the option [use_uncompressed_cache](../settings/settings.md#settings-use_uncompressed_cache) is enabled.
The uncompressed cache is advantageous for very short queries in individual cases.
