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Merge branch 'async_load_system_database' of github.com:ClickHouse/ClickHouse into async_load_system_database

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docs/en/operations/server-configuration-parameters/settings.md
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@ -1977,9 +1977,9 @@ The default is `false`.
## async_load_system_database {#async_load_system_database} ## async_load_system_database {#async_load_system_database}
Asynchronous loading of system tables. Helpful if there is high amount of log tables and parts in system database. Independent of `async_load_databases` setting. Asynchronous loading of system tables. Helpful if there is a high amount of log tables and parts in the `system` database. Independent of the `async_load_databases` setting.
If `true` all system databases with `Ordinary`, `Atomic` and `Replicated` engine will be loaded asynchronously after the ClickHouse server start up. See `system.asynchronous_loader` table, `tables_loader_background_pool_size` and `tables_loader_foreground_pool_size` server settings. Any query that tries to access a system table, that is not yet loaded, will wait for exactly this table to be started up. The table that is waited for by at least one query will be loaded with higher priority. Also consider setting a limit `max_waiting_queries` for the total number of waiting queries. If set to `true`, all system databases with `Ordinary`, `Atomic`, and `Replicated` engines will be loaded asynchronously after the ClickHouse server starts. See `system.asynchronous_loader` table, `tables_loader_background_pool_size` and `tables_loader_foreground_pool_size` server settings. Any query that tries to access a system table, that is not yet loaded, will wait for exactly this table to be started up. The table that is waited for by at least one query will be loaded with higher priority. Also consider setting the `max_waiting_queries` setting to limit the total number of waiting queries.
If `false`, system database loads before server start. If `false`, system database loads before server start.