Cookbook recipe

Fix bad row estimates with extended statistics

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

What This Is

A production experience capsule based on real incident patterns.

Why It Matters

Builds production judgment under pressure.

Next Step

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Estimated investigation4 min

Scenario

The planner badly misjudges rows when two columns are correlated (city and postal code, status and type). CREATE STATISTICS teaches it the correlation. Diagnose it Spot the misestimate, then create multivariate stats: CREATE STATISTICS s_geo (dependencies,…

Investigation Path

The planner badly misjudges rows when two columns are correlated (city and postal code, status and type). CREATE STATISTICS teaches it the correlation.

Diagnose it

Spot the misestimate, then create multivariate stats:

CREATE STATISTICS s_geo (dependencies, ndistinct)
  ON city, postal_code FROM addresses;
ANALYZE addresses;

Why it happens

By default PostgreSQL assumes columns are independent, so it multiplies selectivities. When columns are functionally dependent, that product is far too small — leading to nested-loop plans that explode at runtime.

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Related & next steps

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Concepts on this page

Extended statistics Query planner Index
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