Enables or disables the query planner’s ability to reorder DISTINCT keys to match the input path’s pathkeys.
At a glance
| Property | Value |
|---|---|
| Parameter | enable_distinct_reordering |
| Category | Query Planning |
| Default | on |
| Value type | boolean (on/off) |
| Change scope | Per-session (SET) |
| Available in | PostgreSQL 18, 19 (added in 18) |
What it does
Enables or disables the query planner’s ability to reorder DISTINCT keys to match the input path’s pathkeys. The default is on.
(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 enable_distinct_reordering; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'enable_distinct_reordering';.
Tuning guidance
This is a diagnostic switch, not a production tuning knob. Turn it off briefly (per session) to confirm why the planner avoids or prefers a plan, then leave it on. Forcing it off in production masks bad estimates instead of fixing them — fix statistics, costs or indexes instead.