# autovacuum_max_parallel_workers

> autovacuum_max_parallel_workers — Maximum number of parallel workers that can be used by a single autovacuum worker. Observed in PG19 Beta 3; its last measured boot default is 0 in PG19 Beta 3, with sighup context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Maximum number of parallel workers that can be used by a single autovacuum worker.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `integer` | Upstream pg_settings type |
| Context | `sighup` | Takes effect after configuration reload |
| Unit | — | Raw unit |
| Range | `0` – `1024` | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Vacuuming / Automatic Vacuuming | Upstream classification |
| Latest boot value | `0` | 0 |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG19 Beta 3 |
| Present in | PG19 Beta 3 |
| Removed in | No |
| Introduction commit | [`1ff3180ca016`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=1ff3180ca0169556984ab83759477f593129794d) — Allow autovacuum to use parallel vacuum workers. |
| Commit date | 2026-04-06 |
| Discussion | [thread 1](https://postgr.es/m/CACG=ezZOrNsuLoETLD1gAswZMuH2nGGq7Ogcc0QOE5hhWaw=cw@mail.gmail.com) |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG19 Beta 3 | `0` | — | 0 |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

PostgreSQL describes autovacuum_max_parallel_workers as follows: “Maximum number of parallel workers that can be used by a single autovacuum worker.” A configuration reload applies the value to the server without a full restart. The atlas measures it in PG19 Beta 3; boot_val is the compiled or initialized baseline, not proof of a running cluster's effective setting.

The limit applies per autovacuum worker and only to index vacuuming and index-cleanup phases. Zero disables parallel autovacuum; the actual count is also capped by max_parallel_workers, while each participating worker consumes CPU and maintenance memory.

Read it together with autovacuum_max_workers, autovacuum_worker_slots, max_parallel_workers, maintenance_work_mem. Check SHOW and pg_settings on the target server, verify the source and pending_restart fields, and compare workload, logs, and resource metrics before and after any change.

## Tuning advice {#tuning-advice}

> [!TIP]
> **Advice.** These are workload-specific starting points and must be validated with measurements.

| Workload | Guidance |
| --- | --- |
| OLTP | Start at the upstream default and use pg_stat_autovacuum_scores, table churn, freeze age, queueing, and foreground latency to justify a change. Protect wraparound work and avoid letting a busy-table preference starve quieter tables. |
| OLAP | Batch-heavy systems can benefit from prioritizing the largest maintenance debt or parallelizing index cleanup, but benchmark I/O saturation, maintenance memory, worker contention, and completion time across the whole maintenance window. |
| Small nodes | Keep weights and parallelism conservative. One extra worker can be a large share of CPU, RAM, and storage queue depth; first fix thresholds and ensure autovacuum has enough time to finish. |
{.full-width}

## Pigsty {#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 | — | — |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG19 Beta 3 unmodified; OLAP: PG19 Beta 3 unmodified; CRIT: PG19 Beta 3 unmodified; TINY: PG19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Treating the measured boot_val for autovacuum_max_parallel_workers as proof of the effective value on an initialized or managed cluster.
- Applying a change as though it were immediate while pg_settings reports sighup context.
- Changing this setting in isolation without checking the linked limits, observability, and rollback path.
- Depending on beta behavior in production without retesting the PostgreSQL 19 final release.

## Related parameters {#related-parameters}

[`autovacuum_max_workers`](/parameters/autovacuum-max-workers/) · [`autovacuum_worker_slots`](/parameters/autovacuum-worker-slots/) · [`max_parallel_workers`](/parameters/max-parallel-workers/) · [`maintenance_work_mem`](/parameters/maintenance-work-mem/) · [`autovacuum_work_mem`](/parameters/autovacuum-work-mem/)

## References {#references}

- [PostgreSQL 19 Beta 3 — autovacuum_max_parallel_workers](https://www.postgresql.org/docs/19/runtime-config-vacuum.html#GUC-AUTOVACUUM-MAX-PARALLEL-WORKERS)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)