Parameter · Vacuuming / Automatic Vacuuming

autovacuum_vacuum_cost_delay

Vacuum cost delay in milliseconds, for autovacuum. -1 means use "vacuum_cost_delay".

Default: 2ms
Type: real (ms)
Range: -1 … 100ms
Applies: Reload

In plain words

Autovacuum is throttled by default so it does not disturb your queries: after spending its cost budget a worker naps for 2 ms. Shorter naps or 0 make autovacuum faster; longer naps make it gentler but it may fall behind.

For DBAs and operators

-1 means "use vacuum_cost_delay" (0 by default, i.e. unthrottled). The default was 20 ms up to PostgreSQL 11 and is 2 ms since PostgreSQL 12; configurations carried over from old versions with 20 ms are a classic cause of autovacuum never keeping up.

Per table: ALTER TABLE big SET (autovacuum_vacuum_cost_delay = 0) exempts that table from throttling (and from cost balancing between workers).

Observe

wait_event = 'VacuumDelay' on autovacuum workers in pg_stat_activity.
PostgreSQL 18: track_cost_delay_timing = on adds delay_time to pg_stat_progress_vacuum and to autovacuum log output.
Autovacuum log lines: avg read rate: … MB/s, avg write rate: … MB/s.

How to change it

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

See it in context

Autovacuum: when tables get vacuumed Autovacuum launcher and workers

Related parameters

autovacuum_vacuum_cost_limit vacuum_cost_delay vacuum_cost_limit track_cost_delay_timing

All Vacuuming parameters