autovacuum_vacuum_threshold

For DBAs and operators

The full PostgreSQL 18 rule for update/delete-triggered vacuum is:

vacthresh = autovacuum_vacuum_threshold
          + autovacuum_vacuum_scale_factor * reltuples
vacthresh = min(vacthresh, autovacuum_vacuum_max_threshold)  -- unless -1
vacuum if n_dead_tup > vacthresh

reltuples comes from pg_class (estimated by the last VACUUM/ANALYZE; -1, treated as 0, if never analyzed). n_dead_tup is the cumulative-statistics counter in pg_stat_user_tables; statistics are reset after a crash or pg_stat_reset(), which makes autovacuum "forget" pending work.

Per-table overrides

-- tiny but very hot queue table: vacuum after ~1000 dead rows regardless of size
ALTER TABLE job_queue SET (autovacuum_vacuum_threshold = 1000,
                           autovacuum_vacuum_scale_factor = 0);

Using a large threshold with scale factor 0 gives "vacuum every N changes" behaviour, handy for append-mostly tables with periodic deletes. Toast tables have their own toast.autovacuum_vacuum_threshold.

How to change it

Change in postgresql.conf or ALTER SYSTEM, then run SELECT pg_reload_conf().