enable_material

Definition PG 18 manual

Enables or disables the query planner's use of materialization. It is impossible to suppress materialization entirely, but turning this variable off prevents the planner from inserting materialize nodes except in cases where it is required for correctness. The default is on.

How it works

enable_material controls whether the planner may choose planner-inserted Materialize nodes that preserve an input for rescans or isolate execution properties.

It is consulted while a plan is built. A session-level change is useful for comparing EXPLAIN alternatives, but an already cached plan is not retroactively rewritten; invalidation or replanning is required to observe a different choice.

Turning it off cannot remove materialization that is required for correctness; it only prevents optional planner insertion. Its user context permits session- or transaction-local changes; newly performed or newly planned work sees the value.

Operational considerations

Treating enable_material as a query hint even though it affects every plan built in its scope.

Testing an already cached prepared plan and concluding that the setting has no effect.

Masking stale statistics or cardinality errors by disabling a plan method globally.

Turning it off cannot remove materialization that is required for correctness; it only prevents optional planner insertion.

Workload guidance

OLAP: Benchmark representative analytical plans with and without enable_material. Judge planning time, memory, spill, and execution time together; a win for one report is not evidence for a global setting.

OLTP: Keep the upstream default for routine OLTP. Use a transaction- or session-local change to diagnose whether choosing planner-inserted Materialize nodes that preserve an input for rescans or isolate execution properties explains a regression, then repair statistics, indexes, estimates, or query shape instead of leaving a cluster-wide method ban.

SMALL: Do not use enable_material as a permanent hint on a small host. Resource pressure may change the best method, so verify with EXPLAIN (ANALYZE, BUFFERS) and keep the change scoped to the affected workload if it is still needed.