ClickHouse/docs/en/operations/settings/index.md

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Settings Overview

There are multiple ways to make all the settings described in this section of documentation.

Settings are configured in layers, so each subsequent layer redefines the previous settings.

Ways to configure settings, in order of priority:

• Settings in the users.xml server configuration file.

  Set in the element <profiles>.

• Session settings.

  Send SET setting=value from the ClickHouse console client in interactive mode. Similarly, you can use ClickHouse sessions in the HTTP protocol. To do this, you need to specify the session_id HTTP parameter.

• Query settings.

  • When starting the ClickHouse console client in non-interactive mode, set the startup parameter --setting=value.
  • When using the HTTP API, pass CGI parameters (URL?setting_1=value&setting_2=value...).
  • Make settings in the SETTINGS clause of the SELECT query. The setting value is applied only to that query and is reset to default or previous value after the query is executed.

Settings that can only be made in the server config file are not covered in this section.

Custom Settings

In addition to the common settings, users can define custom settings.

A custom setting name must begin with one of predefined prefixes. The list of these prefixes must be declared in the custom_settings_prefixes parameter in the server configuration file.

<custom_settings_prefixes>custom_</custom_settings_prefixes>

To define a custom setting use SET command:

SET custom_a = 123;

To get the current value of a custom setting use getSetting() function:

SELECT getSetting('custom_a');

See Also

• Server Configuration Settings

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