commit_timestamp_buffers

commit_timestamp_buffers — Sets the size of the dedicated buffer pool used for the commit timestamp cache. Observed in PG17–19 Beta 3; its last measured boot default is 0 B (0 × 8kB) 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 size of the dedicated buffer pool used for the commit timestamp cache.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuepostmaster: Requires a server restart
Unit , Value8kB: Raw unit
Range , Value0 – 131072: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueResource Usage / Memory: Upstream classification
Latest boot value , Value0: 0 B (0 × 8kB)

Lifecycle

Fact	Value
First observed	PG17
Present in	PG17–19 Beta 3
Removed in	No
Introduction commit	`53c2a97a9266` — Improve performance of subsystems on top of SLRU
Commit date	2024-02-28
Discussion	thread 1 · thread 2

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG17–19 Beta 3	`0`	`8kB`	0 B (0 × 8kB)

How it works

commit_timestamp_buffers allocates a dedicated startup-time shared buffer pool for pages in pg_commit_ts, the SLRU area used when commit timestamp tracking is enabled.

A configured zero is an automatic sizing request, not zero memory: PostgreSQL derives shared_buffers/512, clamps it to at least 16 and at most 1024 blocks, and allocates the result at server start.

The cache can reduce pg_commit_ts reads but does not enable commit timestamp collection; track_commit_timestamp is the separate functional switch. Increasing it consumes real shared memory. Its postmaster context fixes the value at server start; changing it requires a restart.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Leave commit_timestamp_buffers at automatic or upstream sizing unless SLRU-specific I/O and contention prove this cache is undersized. A larger number consumes shared memory for the entire server lifetime.
OLAP	Analytical workload labels alone do not justify changing commit_timestamp_buffers; tune only when the underlying transaction-state facility, not table scans, is the measured bottleneck.
Small nodes	Keep commit_timestamp_buffers at its default on a small host. Moving scarce shared memory into an internal cache without direct evidence can reduce room for more valuable caches and processes.

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: PG17–19 Beta 3 unmodified; OLAP: PG17–19 Beta 3 unmodified; CRIT: PG17–19 Beta 3 unmodified; TINY: PG17–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Changing commit_timestamp_buffers without applying its documented unit and configuration context.
Optimizing an isolated benchmark while ignoring concurrent aggregate resource use.
Assuming a configured value guarantees operating-system or storage behavior.
Failing to retest startup, failover, and workload latency after the change.

track_commit_timestamp · shared_buffers · transaction_buffers · subtransaction_buffers