Server Settings

## backup\_threads[​](#backup_threads "Direct link to backup_threads")

The maximum number of threads to execute `BACKUP` requests.

## backups[​](#backups "Direct link to backups")

Settings for backups, used when executing the [`BACKUP` and `RESTORE`](/docs/operations/backup/overview) statements.

The following settings can be configured by sub-tags:

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| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Setting Type Description Default|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `allow_concurrent_backups` Bool Determines whether multiple backup operations can run concurrently on the same host. `true`| `allow_concurrent_restores` Bool Determines whether multiple restore operations can run concurrently on the same host. `true`| `allowed_disk` String Disk to backup to when using `File()`. This setting must be set in order to use `File`. ``|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `allowed_path` String Path to backup to when using `File()`. This setting must be set in order to use `File`. ``|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | `attempts_to_collect_metadata_before_sleep` UInt Number of attempts to collect metadata before sleeping in case of inconsistency after comparing collected metadata. `2`| `collect_metadata_timeout` UInt64 Timeout in milliseconds for collecting metadata during backup. `600000`| `compare_collected_metadata` Bool If true, compares the collected metadata with the existing metadata to ensure they are not changed during backup . `true`| `create_table_timeout` UInt64 Timeout in milliseconds for creating tables during restore. `300000`| `max_attempts_after_bad_version` UInt64 Maximum number of attempts to retry after encountering a bad version error during coordinated backup/restore. `3`| `max_sleep_before_next_attempt_to_collect_metadata` UInt64 Maximum sleep time in milliseconds before the next attempt to collect metadata. `100`| `min_sleep_before_next_attempt_to_collect_metadata` UInt64 Minimum sleep time in milliseconds before the next attempt to collect metadata. `5000`| `remove_backup_files_after_failure` Bool If the `BACKUP` command fails, ClickHouse will try to remove the files already copied to the backup before the failure, otherwise it will leave the copied files as they are. `true`| `sync_period_ms` UInt64 Synchronization period in milliseconds for coordinated backup/restore. `5000`| `test_inject_sleep` Bool Testing related sleep `false`| `test_randomize_order` Bool If true, randomizes the order of certain operations for testing purposes. `false`| `zookeeper_path` String Path in ZooKeeper where backup and restore metadata is stored when using `ON CLUSTER` clause. `/clickhouse/backups` | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |

This setting is configured by default as:

```
<backups>
    ....
</backups>
```

## backups\_io\_thread\_pool\_queue\_size[​](#backups_io_thread_pool_queue_size "Direct link to backups_io_thread_pool_queue_size")

The maximum number of jobs that can be scheduled on the Backups IO Thread pool. It is recommended to keep this queue unlimited due to the current S3 backup logic.

Note

A value of `0` (default) means unlimited.

## bcrypt\_workfactor[​](#bcrypt_workfactor "Direct link to bcrypt_workfactor")

Work factor for the `bcrypt_password` authentication type which uses the [Bcrypt algorithm](https://wildlyinaccurate.com/bcrypt-choosing-a-work-factor/).
The work factor defines the amount of computations and time needed to compute the hash and verify the password.

```
<bcrypt_workfactor>12</bcrypt_workfactor>
```

Note

For applications with high-frequency authentication,
consider alternative authentication methods due to
bcrypt's computational overhead at higher work factors.

## blob\_storage\_log[​](#blob_storage_log "Direct link to blob_storage_log")

Settings for the [`blob_storage_log`](/docs/operations/system-tables/blob_storage_log) system table.

The following settings can be configured by sub-tags: