Set up docs MCPDescription
Contains information about global settings for the server, which are specified in config.xml.
The table also includes supported nested settings with a fixed structure; dynamic sections such as lists are not included.
Columns
name(String) — Server setting name.value(String) — Server setting value.default(String) — Server setting default value.changed(UInt8) — Shows whether a setting was specified in config.xmldescription(String) — Short server setting description.type(String) — Server setting value type.changeable_without_restart(Enum8(‘No’ = 0, ‘IncreaseOnly’ = 1, ‘DecreaseOnly’ = 2, ‘Yes’ = 3)) — Shows whether a setting can be changed at runtime.is_obsolete(UInt8) — Shows whether a setting is obsolete.
Example
The following example shows how to get information about server settings which name contains thread_pool.
SELECT *
FROM system.server_settings
WHERE name LIKE '%thread_pool%'┌─name──────────────────────────────────────────┬─value─┬─default─┬─changed─┬─description─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬─type───┬─changeable_without_restart─┬─is_obsolete─┐
│ max_thread_pool_size │ 10000 │ 10000 │ 0 │ The maximum number of threads that could be allocated from the OS and used for query execution and background operations. │ UInt64 │ No │ 0 │
│ max_thread_pool_free_size │ 1000 │ 1000 │ 0 │ The maximum number of threads that will always stay in a global thread pool once allocated and remain idle in case of insufficient number of tasks. │ UInt64 │ No │ 0 │
│ thread_pool_queue_size │ 10000 │ 10000 │ 0 │ The maximum number of tasks that will be placed in a queue and wait for execution. │ UInt64 │ No │ 0 │
│ max_io_thread_pool_size │ 100 │ 100 │ 0 │ The maximum number of threads that would be used for IO operations │ UInt64 │ No │ 0 │
│ max_io_thread_pool_free_size │ 0 │ 0 │ 0 │ Max free size for IO thread pool. │ UInt64 │ No │ 0 │
│ io_thread_pool_queue_size │ 10000 │ 10000 │ 0 │ Queue size for IO thread pool. │ UInt64 │ No │ 0 │
│ max_active_parts_loading_thread_pool_size │ 64 │ 64 │ 0 │ The number of threads to load active set of data parts (Active ones) at startup. │ UInt64 │ No │ 0 │
│ max_outdated_parts_loading_thread_pool_size │ 32 │ 32 │ 0 │ The number of threads to load inactive set of data parts (Outdated ones) at startup. │ UInt64 │ No │ 0 │
│ max_unexpected_parts_loading_thread_pool_size │ 32 │ 32 │ 0 │ The number of threads to load inactive set of data parts (Unexpected ones) at startup. │ UInt64 │ No │ 0 │
│ max_parts_cleaning_thread_pool_size │ 128 │ 128 │ 0 │ The number of threads for concurrent removal of inactive data parts. │ UInt64 │ No │ 0 │
│ max_backups_io_thread_pool_size │ 1000 │ 1000 │ 0 │ The maximum number of threads that would be used for IO operations for BACKUP queries │ UInt64 │ No │ 0 │
│ max_backups_io_thread_pool_free_size │ 0 │ 0 │ 0 │ Max free size for backups IO thread pool. │ UInt64 │ No │ 0 │
│ backups_io_thread_pool_queue_size │ 0 │ 0 │ 0 │ Queue size for backups IO thread pool. │ UInt64 │ No │ 0 │
└───────────────────────────────────────────────┴───────┴─────────┴─────────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴────────┴────────────────────────────┴─────────────┘Using of WHERE changed can be useful, for example, when you want to check
whether settings in configuration files are loaded correctly and are in use.
SELECT * FROM system.server_settings WHERE changed AND name='max_thread_pool_size'