Cookbook recipe

Custom plan vs generic plan in prepared statements

Applies to PostgreSQL 13–17 Last reviewed May 2026 Grounded in source

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Estimated investigation4 min

Scenario

A prepared statement is fast at first, then suddenly slow after a few executions. PostgreSQL switched from custom plans to a generic plan. Diagnose it Compare planning with explicit prepare/explain: PREPARE p AS SELECT * FROM…

Investigation Path

A prepared statement is fast at first, then suddenly slow after a few executions. PostgreSQL switched from custom plans to a generic plan.

Diagnose it

Compare planning with explicit prepare/explain:

PREPARE p AS SELECT * FROM t WHERE status = ;
EXPLAIN EXECUTE p('rare');   -- first calls: custom plan
-- after ~5 executions PostgreSQL may pick a generic plan

Why it happens

For parameterized statements PostgreSQL builds a custom plan per execution at first, then may cache a single generic plan if it looks no worse on average. For skewed data (a parameter matching 1% vs 90% of rows) the generic plan can be badly wrong.

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Query planner
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