backup_* server settings - ClickHouse Documentation

These settings configure the ClickHouse server and are autogenerated from ClickHouse source.

backup_log

Settings for the backup_log system table for logging BACKUP and RESTORE operations. The following settings can be configured by sub-tags:

Setting	Description	Default	Note
`database`	Name of the database.
`table`	Name of the system table.
`engine`	MergeTree Engine Definition for a system table.		Cannot be used if `partition_by` or `order_by` defined. If not specified `MergeTree` is selected by default
`partition_by`	Custom partitioning key for a system table.		If `engine` is specified for system table, `partition_by` parameter should be specified directly inside ‘engine’
`ttl`	Specifies the table TTL.		If `engine` is specified for system table, `ttl` parameter should be specified directly inside ‘engine’
`order_by`	Custom sorting key for a system table. Can’t be used if `engine` defined.		If `engine` is specified for system table, `order_by` parameter should be specified directly inside ‘engine’
`storage_policy`	Name of the storage policy to use for the table (optional).		If `engine` is specified for system table, `storage_policy` parameter should be specified directly inside ‘engine’
`settings`	Additional parameters that control the behavior of the MergeTree (optional).		If `engine` is specified for system table, `settings` parameter should be specified directly inside ‘engine’
`flush_interval_milliseconds`	Interval for flushing data from the buffer in memory to the table.	`7500`
`max_size_rows`	Maximal size in lines for the logs. When the amount of non-flushed logs reaches the max_size, logs are dumped to the disk.	`1048576`
`reserved_size_rows`	Pre-allocated memory size in lines for the logs.	`8192`
`buffer_size_rows_flush_threshold`	Threshold for amount of lines. If the threshold is reached, flushing logs to the disk is launched in background.	`max_size_rows / 2`
`flush_on_crash`	Sets whether logs should be dumped to the disk in case of a crash.	`false`

Additionally, the following server-level setting controls the default flush policy for all system log tables:

<default_system_log_flush_policy>
    <skip_alias_columns>true</skip_alias_columns>
</default_system_log_flush_policy>

Setting	Description	Default
`skip_alias_columns`	When `true`, ALIAS columns are omitted from system log table schemas. Required for S3-backed system logs.	`false`

Example

<clickhouse>
    <backup_log>
        <database>system</database>
        <table>backup_log</table>
        <flush_interval_milliseconds>1000</flush_interval_milliseconds>
        <partition_by>toYYYYMM(event_date)</partition_by>
        <max_size_rows>1048576</max_size_rows>
        <reserved_size_rows>8192</reserved_size_rows>
        <buffer_size_rows_flush_threshold>524288</buffer_size_rows_flush_threshold>
        <flush_on_crash>false</flush_on_crash>
        <!-- <engine>Engine = MergeTree PARTITION BY event_date ORDER BY event_time TTL event_date + INTERVAL 30 day</engine> -->
    </backup_log>
</clickhouse>

backup_threads

The maximum number of threads to execute BACKUP requests.

Last modified on July 22, 2026