Server Settings

List of prefixes used for [custom settings](/docs/operations/settings/query-level#custom_settings).
Multiple prefixes should be separated by commas.

**Example**

```
<custom_settings_prefixes>SQL_</custom_settings_prefixes>
```

**See Also**

- [Custom settings](/docs/operations/settings/query-level#custom_settings)

## database\_atomic\_delay\_before\_drop\_table\_sec[​](#database_atomic_delay_before_drop_table_sec "Direct link to database_atomic_delay_before_drop_table_sec")

The delay during which a dropped table can be restored using the [`UNDROP`](/docs/sql-reference/statements/undrop) statement. If `DROP TABLE` ran with a `SYNC` modifier, the setting is ignored.
The default for this setting is `480` (8 minutes).

## database\_catalog\_drop\_error\_cooldown\_sec[​](#database_catalog_drop_error_cooldown_sec "Direct link to database_catalog_drop_error_cooldown_sec")

In case of a failed table drop, ClickHouse will wait for this time-out before retrying the operation.

## database\_catalog\_drop\_table\_concurrency[​](#database_catalog_drop_table_concurrency "Direct link to database_catalog_drop_table_concurrency")

The size of the threadpool used for dropping tables.

## database\_catalog\_unused\_dir\_cleanup\_period\_sec[​](#database_catalog_unused_dir_cleanup_period_sec "Direct link to database_catalog_unused_dir_cleanup_period_sec")

Parameter of a task that cleans up garbage from `store/` directory.
Sets scheduling period of the task.

Note

A value of `0` means "never". The default value corresponds to 1 day.

## database\_catalog\_unused\_dir\_hide\_timeout\_sec[​](#database_catalog_unused_dir_hide_timeout_sec "Direct link to database_catalog_unused_dir_hide_timeout_sec")

Parameter of a task that cleans up garbage from `store/` directory.
If some subdirectory is not used by clickhouse-server and this directory was not modified for last
[`database_catalog_unused_dir_hide_timeout_sec`](/docs/operations/server-configuration-parameters/settings#database_catalog_unused_dir_hide_timeout_sec) seconds, the task will "hide" this directory by
removing all access rights. It also works for directories that clickhouse-server does not
expect to see inside `store/`.

Note

A value of `0` means "immediately".

## database\_catalog\_unused\_dir\_rm\_timeout\_sec[​](#database_catalog_unused_dir_rm_timeout_sec "Direct link to database_catalog_unused_dir_rm_timeout_sec")

Parameter of a task that cleans up garbage from `store/` directory.
If some subdirectory is not used by clickhouse-server and it was previously "hidden"
(see [database\_catalog\_unused\_dir\_hide\_timeout\_sec](/docs/operations/server-configuration-parameters/settings#database_catalog_unused_dir_hide_timeout_sec))
and this directory was not modified for last
[`database_catalog_unused_dir_rm_timeout_sec`]/operations/server-configuration-parameters/settings#database\_catalog\_unused\_dir\_rm\_timeout\_sec) seconds, the task will remove this directory.
It also works for directories that clickhouse-server does not
expect to see inside `store/`.

Note

A value of `0` means "never". The default value corresponds to 30 days.

## database\_replicated\_allow\_detach\_permanently[​](#database_replicated_allow_detach_permanently "Direct link to database_replicated_allow_detach_permanently")

Allow detaching tables permanently in Replicated databases

## database\_replicated\_drop\_broken\_tables[​](#database_replicated_drop_broken_tables "Direct link to database_replicated_drop_broken_tables")

Drop unexpected tables from Replicated databases instead of moving them to a separate local database

## dead\_letter\_queue[​](#dead_letter_queue "Direct link to dead_letter_queue")

Setting for the 'dead\_letter\_queue' system table.

The following settings can be configured by sub-tags: