What causes PostgreSQL to choose sequential scan over index?

Poor selectivity—when your WHERE grabs most rows, random I/O jumps cost more than steady seq read. Tune stats with ANALYZE.

How do I force PostgreSQL to use an index?

Don't—it's usually wrong. But disable_seqscan=on for testing, or use partial indexes for selective cases.

Nope. Depends on costs. Benchmark with EXPLAIN ANALYZE; partition if seq dominates huge ranges.

☁️ Cloud & Databases

Sie bauen den perfekten Index. Starten die Query. Stille. Postgres seq-scant trotzdem Ihre Millionen-Tabelle. Warum – und wie Sie dagegen vorgehen.

Open Source Beat Apr 11, 2026 4 min read

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Postgres wählt Pläne nach Gesamtkosten, nicht Index-Präsenz – Seq-Scans siegen bei schlechter Selectivity. 𝕏
Mit ANALYZE, Partial-Indexen und Partitioning Indexe wieder brauchbar machen. 𝕏
Denken wie Postgres: I/O minimieren, Hype um 'Immer indexen' ignorieren. 𝕏

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#EXPLAIN ANALYZE #PostgreSQL #database indexes #query-optimization

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Originally reported by Dev.to