enable_nestloop — PostgreSQL configuration parameter

Enables or disables the query planner’s use of nested-loop join plans.

At a glance

What it does

Enables or disables the query planner’s use of nested-loop join plans. It is impossible to suppress nested-loop joins entirely, but turning this variable off discourages the planner from using one if there are other methods available. 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_nestloop; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'enable_nestloop';.

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.

Reference

PostgreSQL documentation — enable_nestloop.