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Table Statistics

The database samples each table to record row count, per-column distinct-value counts, most-common values with frequencies, and histograms; ANALYZE (or auto-analyze) refreshes them. These numbers are the optimizer's only knowledge of the data, so stale statistics after a bulk load are a classic cause of sudden plan regressions.

Questions this Concept answers

Why does the planner rely on a sampled statistical sketch instead of counting matching rows before it plans?

jeremy Video

How pg_stats Column Statistics Drive Planner Cost Estimates in PostgreSQL

PostgreSQL's cost-based query planner does not consult table data when choosing a plan; it consults column-level statistics stored in `pg_statistic` (exposed human-readably through the `pg_stats` vie…