Core conceptsadvanced
Visibility map
A compact structure that records whether a heap page is all-visible or all-frozen, which helps PostgreSQL skip unnecessary heap checks.
What this means
A tiny index of the table that flags which pages are "every row here is visible to everyone", nothing dead or in-progress to worry about. When a query or vacuum sees that flag, it can trust the page and skip opening it, which saves real work on big read-heavy tables. It's a green sticker on the pages that don't need re-checking.
Why it matters operationally
It directly affects index-only scans, autovacuum efficiency, and the latency profile of read-heavy tables.
Related errors
Where it lives in the source
src/backend/access/heap/visibilitymap.c