Controls the selection bias used by GEQO.
At a glance
| Property | Value |
|---|---|
| Parameter | geqo_selection_bias |
| Category | Query Planning |
| Default | (see documentation) |
| Value type | floating point |
| Change scope | Per-session (SET) |
| Available in | PostgreSQL 12, 13, 14, 15, 16, 17, 18, 19 (added in 12) |
What it does
Controls the selection bias used by GEQO. The selection bias is the selective pressure within the population. Values can be from 1.50 to 2.00; the latter is the default.
(Description quoted from the official PostgreSQL documentation.)
How to apply a change
Can be set per session with SET, per role/database with ALTER ROLE/DATABASE ... SET, or globally in postgresql.conf.
Inspect the current value and source with SHOW geqo_selection_bias; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'geqo_selection_bias';.
Tuning guidance
This parameter is rarely a performance lever. Leave it at the default unless you have a specific, documented reason to change it, change it on one session or one role/database first, and confirm the effect with pg_settings and your own measurements before rolling it out cluster-wide.