commit_delay

commit_delay — Sets the delay in microseconds between transaction commit and flushing WAL to disk. Observed in PG9.0–19 Beta 3; its last measured boot default is 0 in PG19 Beta 3, with superuser context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Sets the delay in microseconds between transaction commit and flushing WAL to disk.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuesuperuser: Settable at runtime by a superuser
Unit , Value—: Raw unit
Range , Value0 – 100000: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueWrite-Ahead Log / Settings: Upstream classification
Latest boot value , Value0: 0

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

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

How it works

Sets the delay in microseconds between transaction commit and flushing WAL to disk. A superuser or a role granted SET privilege can change it for the relevant session or configuration scope.

A backend that is about to flush commit WAL may wait this many microseconds so concurrent commits can join the same durable flush. The delay is considered only when at least commit_siblings other transactions are active, trading individual latency for possible group-commit efficiency.

Monitor and change commit_delay together with commit_siblings, synchronous_commit, wal_writer_delay. Validate on the relevant server role and real workload, then use its superuser 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	Benchmark commit_delay 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.

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	`20`	different	`20`
OLAP	`20`	different	`20`
CRIT	`20`	different	`20`
TINY	`20`	different	`20`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 20 (dcs); OLAP: PG9.0–19 Beta 3 = 20 (dcs); CRIT: PG9.0–19 Beta 3 = 20 (dcs); TINY: PG9.0–19 Beta 3 = 20 (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to encourage very short group-commit batching under concurrent commit load; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

Common pitfalls

Setting a delay while commit_siblings prevents it from being reached under the real concurrency level.
Reading the value as milliseconds even though the unit is microseconds.
Increasing average group-commit throughput while violating p95 or p99 commit-latency objectives.
Expecting a delay when the commit path does not need to flush WAL.
Changing commit_delay without measuring it together with commit_siblings and WALSync waits.

commit_siblings · synchronous_commit · wal_writer_delay · wal_sync_method · fsync · full_page_writes