# commit_siblings

> commit_siblings — Sets the minimum number of concurrent open transactions required before performing "commit_delay". Observed in PG9.0–19 Beta 3; its last measured boot default is 5 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:** “Sets the minimum number of concurrent open transactions required before performing "commit_delay".”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `integer` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | `0` – `1000` | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Write-Ahead Log / Settings | Upstream classification |
| Latest boot value | `5` | 5 |
{.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 | `5` | — | 5 |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

Sets the minimum number of concurrent open transactions required before performing "commit_delay". It can be changed at session scope, so different sessions may observe different behavior.

This is the concurrency gate for commit_delay, counted from other active transactions when a commit flush is needed. It is not a count of commits already waiting and has no useful effect while commit_delay is zero.

Monitor and change commit_siblings together with commit_delay, synchronous_commit, wal_writer_delay. 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 | Benchmark commit_siblings only under high commit concurrency with material WALSync waits and an acceptable p95/p99 latency budget. Tune commit_delay and commit_siblings as a pair and retain a zero-delay baseline. |
| OLAP | Bulk jobs should usually reduce commit frequency with sensible transaction batches; do not use group-commit delay to compensate for row-at-a-time ETL commits. |
| Small nodes | Low concurrency provides little opportunity, so commit_delay=0 is simplest. Even a microsecond value needs end-to-end latency evidence. |
{.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 | `10` | different | `10` |
| OLAP | `10` | different | `10` |
| CRIT | `10` | different | `10` |
| TINY | `10` | different | `10` |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 10 (dcs); OLAP: PG9.0–19 Beta 3 = 10 (dcs); CRIT: PG9.0–19 Beta 3 = 10 (dcs); TINY: PG9.0–19 Beta 3 = 10 (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to apply commit_delay only after the server has substantial concurrent transaction activity; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

## Common pitfalls {#common-pitfalls}

- Tuning it while commit_delay is zero, in which case the threshold has no effect.
- Treating it as a count of commits already waiting rather than other active transactions.
- Setting the gate too low and adding latency during ordinary moderate concurrency.
- Applying a session-level experiment globally without comparing commit latency and WALSync behavior.

## Related parameters {#related-parameters}

[`commit_delay`](/parameters/commit-delay/) · [`synchronous_commit`](/parameters/synchronous-commit/) · [`wal_writer_delay`](/parameters/wal-writer-delay/) · [`wal_sync_method`](/parameters/wal-sync-method/) · [`fsync`](/parameters/fsync/) · [`full_page_writes`](/parameters/full-page-writes/)

## References {#references}

- [PostgreSQL 19 Beta 3 — commit_siblings](https://www.postgresql.org/docs/19/runtime-config-wal.html#GUC-COMMIT-SIBLINGS)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)