Server Settings

## http\_server\_default\_response[​](#http_server_default_response "Direct link to http_server_default_response")

The page that is shown by default when you access the ClickHouse HTTP(s) server.
The default value is "Ok." (with a line feed at the end)

**Example**

Opens `https://tabix.io/` when accessing `http://localhost: http_port`.

```
<http_server_default_response>
  <![CDATA[<html ng-app="SMI2"><head><base href="http://ui.tabix.io/"></head><body><div ui-view="" class="content-ui"></div><script src="http://loader.tabix.io/master.js"></script></body></html>]]>
</http_server_default_response>
```

## iceberg\_background\_schedule\_pool\_size[​](#iceberg_background_schedule_pool_size "Direct link to iceberg_background_schedule_pool_size")

Size of thread pool to asynchronously fetch the latest metadata from a remote iceberg catalog; the pool is shared by all the active tables.

## iceberg\_catalog\_threadpool\_pool\_size[​](#iceberg_catalog_threadpool_pool_size "Direct link to iceberg_catalog_threadpool_pool_size")

Size of background pool for iceberg catalog

## iceberg\_catalog\_threadpool\_queue\_size[​](#iceberg_catalog_threadpool_queue_size "Direct link to iceberg_catalog_threadpool_queue_size")

Number of tasks which is possible to push into iceberg catalog pool

## iceberg\_metadata\_files\_cache\_max\_entries[​](#iceberg_metadata_files_cache_max_entries "Direct link to iceberg_metadata_files_cache_max_entries")

Maximum size of iceberg metadata files cache in entries. Zero means disabled.

## iceberg\_metadata\_files\_cache\_policy[​](#iceberg_metadata_files_cache_policy "Direct link to iceberg_metadata_files_cache_policy")

Iceberg metadata cache policy name.

## iceberg\_metadata\_files\_cache\_size[​](#iceberg_metadata_files_cache_size "Direct link to iceberg_metadata_files_cache_size")

Maximum size of iceberg metadata cache in bytes. Zero means disabled.

## iceberg\_metadata\_files\_cache\_size\_ratio[​](#iceberg_metadata_files_cache_size_ratio "Direct link to iceberg_metadata_files_cache_size_ratio")

The size of the protected queue (in case of SLRU policy) in the iceberg metadata cache relative to the cache's total size.

## ignore\_empty\_sql\_security\_in\_create\_view\_query[​](#ignore_empty_sql_security_in_create_view_query "Direct link to ignore_empty_sql_security_in_create_view_query")

If true, ClickHouse doesn't write defaults for empty SQL security statement in `CREATE VIEW` queries.

Note

This setting is only necessary for the migration period and will become obsolete in 24.4

## include\_from[​](#include_from "Direct link to include_from")

The path to the file with substitutions. Both XML and YAML formats are supported.

For more information, see the section [Configuration files](/docs/operations/configuration-files).

**Example**

```
<include_from>/etc/metrica.xml</include_from>
```

## index\_mark\_cache\_policy[​](#index_mark_cache_policy "Direct link to index_mark_cache_policy")

Secondary index mark cache policy name.

## index\_mark\_cache\_prewarm\_ratio[​](#index_mark_cache_prewarm_ratio "Direct link to index_mark_cache_prewarm_ratio")

The ratio of total size of index mark cache to fill during prewarm.

## index\_mark\_cache\_size[​](#index_mark_cache_size "Direct link to index_mark_cache_size")

Maximum size of cache for index marks.

Note

A value of `0` means disabled.

This setting can be modified at runtime and will take effect immediately.

## index\_mark\_cache\_size\_ratio[​](#index_mark_cache_size_ratio "Direct link to index_mark_cache_size_ratio")

The size of the protected queue (in case of SLRU policy) in the secondary index mark cache relative to the cache's total size.

## index\_uncompressed\_cache\_policy[​](#index_uncompressed_cache_policy "Direct link to index_uncompressed_cache_policy")

Secondary index uncompressed cache policy name.

## index\_uncompressed\_cache\_size[​](#index_uncompressed_cache_size "Direct link to index_uncompressed_cache_size")

Maximum size of cache for uncompressed blocks of `MergeTree` indices.

Note

A value of `0` means disabled.

This setting can be modified at runtime and will take effect immediately.

## index\_uncompressed\_cache\_size\_ratio[​](#index_uncompressed_cache_size_ratio "Direct link to index_uncompressed_cache_size_ratio")

The size of the protected queue (in case of SLRU policy) in the secondary index uncompressed cache relative to the cache's total size.

## insert\_deduplication\_version[​](#insert_deduplication_version "Direct link to insert_deduplication_version")

This setting makes it possible to migrate from the code version which makes insert deduplication for sync and async inserts totally different not transparent way to the code version where inserted data would be deduplicated across sync and async inserts.
The value `old_separate_hashes` means that ClickHouse will use different deduplication hashes for sync and async inserts (the same as before).
This value should be used as a default value if there is no intention to start migration.
The value `compatible_double_hashes` means that ClickHouse will use two deduplication hashes: the old one for sync or async inserts and another the new one for all inserts. This value should be used to migrate existing instances to the new behavior in a safe way.
This value should be enabled for some time (see replicated\_deduplication\_window and non\_replicated\_deduplication\_window settings) to make sure that no sync or async inserts are lost during migration.
Finally the value `new_unified_hash` means that ClickHouse will use the new deduplication hash for sync and async inserts. This value could be enabled on new instances of ClickHouse or on instances which already used `compatible_double_hashes` value for some time.
The default would be set to `compatible_double_hashes` and then later to `new_unified_hash` in future versions of ClickHouse in order to complete the migration in a safe way in two reases.

## interserver\_http\_credentials[​](#interserver_http_credentials "Direct link to interserver_http_credentials")

A username and a password used to connect to other servers during [replication](/docs/engines/table-engines/mergetree-family/replication). Additionally, the server authenticates other replicas using these credentials.
`interserver_http_credentials` must therefore be the same for all replicas in a cluster.

Note

- By default, if `interserver_http_credentials` section is omitted, authentication is not used during replication.
- `interserver_http_credentials` settings do not relate to a ClickHouse client credentials [configuration](/docs/interfaces/client#configuration_files).
- These credentials are common for replication via `HTTP` and `HTTPS`.

The following settings can be configured by sub-tags:

- `user` — Username.
- `password` — Password.
- `allow_empty` — If `true`, then other replicas are allowed to connect without authentication even if credentials are set. If `false`, then connections without authentication are refused. Default: `false`.
- `old` — Contains old `user` and `password` used during credential rotation. Several `old` sections can be specified.

**Credentials Rotation**

ClickHouse supports dynamic interserver credentials rotation without stopping all replicas at the same time to update their configuration. Credentials can be changed in several steps.

To enable authentication, set `interserver_http_credentials.allow_empty` to `true` and add credentials. This allows connections with authentication and without it.

```
<interserver_http_credentials>
    <user>admin</user>
    <password>111</password>
    <allow_empty>true</allow_empty>
</interserver_http_credentials>
```

After configuring all replicas set `allow_empty` to `false` or remove this setting. It makes authentication with new credentials mandatory.

To change existing credentials, move the username and the password to `interserver_http_credentials.old` section and update `user` and `password` with new values. At this point the server uses new credentials to connect to other replicas and accepts connections with either new or old credentials.