autovacuum_worker_slots

autovacuum_worker_slots — Sets the number of backend slots to allocate for autovacuum workers. Observed in PG18–19 Beta 3; its last measured boot default is 16 in PG19 Beta 3, with postmaster context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Sets the number of backend slots to allocate for autovacuum workers.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuepostmaster: Requires a server restart
Unit , Value—: Raw unit
Range , Value1 – 262143: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueVacuuming / Automatic Vacuuming: Upstream classification
Latest boot value , Value16: 16

Lifecycle

Fact	Value
First observed	PG18
Present in	PG18–19 Beta 3
Removed in	No
Introduction commit	`c758119e5bfb` — Allow changing autovacuum_max_workers without restarting.
Commit date	2025-01-06
Discussion	thread 1

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG18–19 Beta 3	`16`	—	16

How it works

Sets the number of backend slots to allocate for autovacuum workers. The value is fixed when the server starts, so changing it requires a restart.

PG18 separates the startup allocation of backend slots for autovacuum workers from the active concurrency limit autovacuum_max_workers. The slots are reserved at startup so the worker limit can be reloaded within that allocation.

Monitor and change autovacuum_worker_slots together with autovacuum, autovacuum_naptime, autovacuum_max_workers. Validate on the relevant server role and real workload, then use its postmaster context to choose session change, reload, or restart; a historical boot default is not the current effective value.

Tuning advice

Tip

Advice. These are workload-specific starting points and must be validated with measurements.

Workload	Guidance
OLTP	Tune autovacuum_worker_slots from table size, change rate, and maintenance SLA, using per-table thresholds for large/hot relations. Observe trigger intervals, dead tuples, and ANALYZE/VACUUM duration.
OLAP	Run explicit ANALYZE/VACUUM after bulk loads instead of waiting only for proportional triggers; plan freezing and visibility-map advancement separately for append-only partitions.
Small nodes	Start with upstream or the measured Pigsty matrix value. Fixed thresholds dominate on small tables; after changes, confirm worker and I/O headroom.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

Template	Effective value	Versus upstream boot	Source expression
OLTP	Unmodified	—	—
OLAP	Unmodified	—	—
CRIT	Unmodified	—	—
TINY	Unmodified	—	—

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG18–19 Beta 3 unmodified; OLAP: PG18–19 Beta 3 unmodified; CRIT: PG18–19 Beta 3 unmodified; TINY: PG18–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Changing the global value while a table storage parameter overrides it.
Treating reltuples and cumulative change statistics as exact real-time counts.
Blaming a threshold without checking long transactions, replication slots, and worker saturation.
Buying short-term quiet by deferring maintenance until wraparound failsafe activates.

autovacuum · autovacuum_naptime · autovacuum_max_workers · autovacuum_work_mem · track_counts · autovacuum_analyze_scale_factor