12th September 2019: PostgreSQL 12 Beta 4 Released!
Supported Versions: Current (11) / 10 / 9.6 / 9.5 / 9.4
Development Versions: 12 / devel
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18.4. Database Configuration

Recall from Section 16.4 that the PostgreSQL server provides a large number of run-time configuration variables. You can set database-specific default values for many of these settings.

For example, if for some reason you want to disable the GEQO optimizer for a given database, you'd ordinarily have to either disable it for all databases or make sure that every connecting client is careful to issue SET geqo TO off;. To make this setting the default you can execute the command

ALTER DATABASE mydb SET geqo TO off;

This will save the setting (but not set it immediately) and in subsequent connections it will appear as though SET geqo TO off; had been called right before the session started. Note that users can still alter this setting during the session; it will only be the default. To undo any such setting, use ALTER DATABASE dbname RESET varname;.