Understanding PostgreSQL VACUUM at the Page Level: Dead Tuple Lifecycle and Space Reclamation
By
Radim Marek
Summary
This article provides an in-depth technical exploration of VACUUM operations at the page level in PostgreSQL databases. It explains how VACUUM handles dead tuple cleanup beyond what HOT (Heap-Only Tuple) pruning can achieve, covering cold updates, DELETEs, index entry cleanup, free space map registration, and visibility map maintenance. The article uses tools like pageinspect, pg_freespace, and pg_visibility to demonstrate the lifecycle of a dead tuple — from losing its storage, to index entry removal, to slot reclamation, and eventual space reuse.
Source
Hacker NewsUnderstanding PostgreSQL VACUUM at the Page Level: Dead Tuple Lifecycle and Space Reclamationboringsql.comKey quotes
· 3 pulledFor everything else (cold updates that touch indexed columns, plain DELETEs, index entry cleanup, free space map registration, visibility map maintenance) we need VACUUM.
Pruning is exactly that: a shortcut. It only works within a single page, and only for HOT-updated tuples.
Watch a VACUUM cycle with pageinspect, pg_freespace, and pg_visibility: how a dead tuple loses its storage, then its index entry, then its slot, and how the freed space gets reused.
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