ClickHouse/docs/en/operations/system-tables/server_settings.md

slug
/en/operations/system-tables/server_settings

server_settings

Contains information about global settings for the server, which were specified in config.xml. Currently, the table shows only settings from the first layer of config.xml and doesn't support nested configs (e.g. logger).

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.xml
• description (String) — Short server setting description.
• type (String) — Server setting value type.

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───┐
│ max_thread_pool_size         │ 5000  │ 10000   │       1 │ The maximum number of threads that could be allocated from the OS and used for query execution and background operations.                           │ UInt64 │
│ 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 │
│ thread_pool_queue_size       │ 10000 │ 10000   │       0 │ The maximum number of tasks that will be placed in a queue and wait for execution.                                                                  │ UInt64 │
│ max_io_thread_pool_size      │ 100   │ 100     │       0 │ The maximum number of threads that would be used for IO operations                                                                                  │ UInt64 │
│ max_io_thread_pool_free_size │ 0     │ 0       │       0 │ Max free size for IO thread pool.                                                                                                                   │ UInt64 │
│ io_thread_pool_queue_size    │ 10000 │ 10000   │       0 │ Queue size for IO thread pool.                                                                                                                      │ UInt64 │
└──────────────────────────────┴───────┴─────────┴─────────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴────────┘

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'

See also

• Settings
• Configuration Files
• Server Settings