# vacuum_cost_limit

> vacuum_cost_limit — Vacuum cost amount available before napping. Observed in PG9.0–19 Beta 3; its last measured boot default is 200 in PG19 Beta 3, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Vacuum cost amount available before napping.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `integer` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | `1` – `10000` | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Vacuuming / Cost-Based Vacuum Delay | Upstream classification |
| Latest boot value | `200` | 200 |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG9.0 (research boundary) |
| Present in | PG9.0–19 Beta 3 |
| Removed in | No |
| Introduction commit | Not asserted: predates the PG9.0 research boundary |
| Commit date | — |
| Discussion | — |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG9.0–19 Beta 3 | `200` | — | 200 |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

Vacuum cost amount available before napping. It can be changed at session scope, so different sessions may observe different behavior.

VACUUM accumulates virtual cost for page hits, misses, and dirties; after the balance reaches vacuum_cost_limit it sleeps for vacuum_cost_delay and resets. This is coarse I/O pacing rather than an exact bandwidth cap, and the wraparound failsafe bypasses throttling.

Monitor and change vacuum_cost_limit together with vacuum_cost_delay, vacuum_cost_page_hit, vacuum_cost_page_miss. Validate on the relevant server role and real workload, then use its user context to choose session change, reload, or restart; a historical boot default is not the current effective value.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Tune vacuum_cost_limit from autovacuum duration, dead-tuple growth, and foreground I/O latency together. Prefer per-table overrides for hotspots; global throttling must not let cleanup fall permanently behind. |
| OLAP | During post-load windows, a larger budget or shorter delay can improve maintenance throughput, but verify that scans do not starve queries/imports. Failsafe activation means normal pacing already failed. |
| Small nodes | Keep conservative defaults. On slow disks, lowering concurrency or overriding one table is usually more controllable than making the delay arbitrarily large. |
{.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 | `2000` | different | `2000` |
| OLAP | `10000` | different | `10000` |
| CRIT | `2000` | different | `2000` |
| TINY | `2000` | different | `2000` |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 2000 (dcs); OLAP: PG9.0–19 Beta 3 = 10000 (dcs); CRIT: PG9.0–19 Beta 3 = 2000 (dcs); TINY: PG9.0–19 Beta 3 = 2000 (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to pair the delay with a much larger work budget, especially for OLAP maintenance; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

## Common pitfalls {#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.

## Related parameters {#related-parameters}

[`vacuum_cost_delay`](/parameters/vacuum-cost-delay/) · [`vacuum_cost_page_hit`](/parameters/vacuum-cost-page-hit/) · [`vacuum_cost_page_miss`](/parameters/vacuum-cost-page-miss/) · [`vacuum_cost_page_dirty`](/parameters/vacuum-cost-page-dirty/) · [`autovacuum_vacuum_cost_delay`](/parameters/autovacuum-vacuum-cost-delay/) · [`autovacuum_vacuum_cost_limit`](/parameters/autovacuum-vacuum-cost-limit/)

## References {#references}

- [PostgreSQL 19 Beta 3 — vacuum_cost_limit](https://www.postgresql.org/docs/19/runtime-config-vacuum.html#GUC-VACUUM-COST-LIMIT)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)