Cookbook recipe

Why your query ignores the index (and how to fix it)

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

You created the perfect index but EXPLAIN still shows a sequential scan. The planner is not broken — something about the query or statistics is steering it away. Diagnose it Compare the estimate to reality: EXPLAIN…

Investigation Path

You created the perfect index but EXPLAIN still shows a sequential scan. The planner is not broken — something about the query or statistics is steering it away.

Diagnose it

Compare the estimate to reality:

EXPLAIN (ANALYZE, BUFFERS)
SELECT * FROM orders WHERE status = 'open';

Watch for a function or type mismatch wrapped around the column, or a wildly wrong row estimate.

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Career Impact

This scenario builds production judgment and operational confidence under pressure.

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Related & next steps

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Keyset pagination instead of OFFSET Speed up COUNT(*) on large tables Detecting and stopping a runaway query HOT updates and why fillfactor matters BRIN indexes for huge append-only tables

Concepts on this page

Extended statistics Query planner Selectivity Autovacuum Index
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