Cookbook recipe

HOT updates and why fillfactor matters

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

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Estimated investigation4 min

Scenario

Update-heavy tables bloat their indexes fast — unless HOT (Heap-Only Tuple) updates kick in. Fillfactor leaves room for them. Diagnose it Check the HOT update ratio: SELECT relname, n_tup_upd, n_tup_hot_upd, round(100*n_tup_hot_upd/greatest(n_tup_upd,1),1) AS hot_pct FROM pg_stat_user_tables ORDER…

Investigation Path

Update-heavy tables bloat their indexes fast — unless HOT (Heap-Only Tuple) updates kick in. Fillfactor leaves room for them.

Diagnose it

Check the HOT update ratio:

SELECT relname, n_tup_upd, n_tup_hot_upd,
  round(100*n_tup_hot_upd/greatest(n_tup_upd,1),1) AS hot_pct
FROM pg_stat_user_tables ORDER BY n_tup_upd DESC LIMIT 10;

Why it happens

A HOT update places the new row version on the same page and avoids touching indexes — but only if no indexed column changed and the page has free space. A full page forces a non-HOT update that adds index entries (bloat).

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Related & next steps

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Concepts on this page

fillfactor Heap-Only Tuple (HOT) Autovacuum VACUUM Index
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