Core conceptsintermediate
Table statistics (ANALYZE)
Sampled distributions of column values stored in pg_statistic that the planner uses to estimate row counts and choose plans.
What this means
Postgres doesn't re-count your whole table to plan a query, it keeps a sampled sketch of each column: which values are common, how they're spread out. ANALYZE builds that sketch, and the planner leans on it to guess how many rows a filter will match. Stale statistics are how good queries start choosing bad plans.
Why it matters operationally
Stale or missing statistics are a leading cause of sudden bad plans; ANALYZE is often the cheapest performance fix.
Related errors
Where it lives in the source
src/backend/commands/analyze.c