Max FROM items before the planner stops reordering joins.
At a glance
| Property | Value |
|---|---|
| Parameter | join_collapse_limit |
| Category | Query Planner |
| Default | 8 |
| Value type | boolean / enum / numeric |
| Change scope | Per-session (SET) |
What it does
Above this many tables in a join, the planner stops exhaustively reordering and follows the written join order, trading plan quality for planning time.
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 join_collapse_limit; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'join_collapse_limit';.
Tuning guidance
Raise (e.g. 12-16) for big star/snowflake joins where a better plan justifies longer planning. Keep from_collapse_limit in step.