Why does PostgreSQL choose sequential scan over index?

Postgres picks seq scan when most rows match (low selectivity)—random I/O from index jumps costs more than one linear pass.

How to make PostgreSQL use my index?

Improve selectivity with better WHERE, run ANALYZE for stats, tune random_page_cost for SSDs. Avoid forcing unless desperate.

What is index selectivity in PostgreSQL?

Fraction of rows your condition hits. Under ~5-10%? Index shines. Above? Seq scan often cheaper.

🗄️ Databases & Backend

Why PostgreSQL Ghosts Your Index — And the Hidden Math That Decides

You slap an index on that PostgreSQL table, hit run, and... crickets. Same sluggish query. Here's the brutal truth: Postgres doesn't worship indexes—it crunches cold, hard costs.

DevTools Feed Apr 11, 2026 3 min read

PostgreSQL EXPLAIN plan showing sequential scan ignoring index on large table

⚡ Key Takeaways

Postgres optimizes for total I/O cost, not index existence—seq scans win on loose filters. 𝕏
Tune random_page_cost and ANALYZE stats to align planner with your hardware. 𝕏
Think like the planner: minimum work, not 'clever' structures. 𝕏

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#EXPLAIN ANALYZE #PostgreSQL #database indexes #query optimization

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