wal_buffers

wal_buffers — Sets the number of disk-page buffers in shared memory for WAL. Observed in PG9.0–19 Beta 3; its last measured boot default is -1 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 number of disk-page buffers in shared memory for WAL.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuepostmaster: Requires a server restart
Unit , Value8kB: Raw unit
Range , Value-1 – 262143: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueWrite-Ahead Log / Settings: Upstream classification
Latest boot value , Value-1: -1 8kB

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	`8`	`8kB`	64 KiB (8 × 8kB)
PG9.1–19 Beta 3	`-1`	`8kB`	-1 8kB

How it works

Sets the number of disk-page buffers in shared memory for WAL. The value is fixed when the server starts, so changing it requires a restart.

The automatic -1 value chooses about 1/32 of shared_buffers, bounded below and by one WAL segment. The buffer absorbs WAL records before writes; too little can add WALWrite pressure during bursts, while oversized allocation consumes startup shared memory without replacing durable flushes.

Monitor and change wal_buffers together with fsync, full_page_writes, wal_sync_method. Validate on the relevant server role and real workload, then use its postmaster 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	Establish durability and recovery objectives first, then tune wal_buffers from WAL rate, flush latency, checkpoints, and peak pg_wal usage. Validate every change with crash/recovery and archive monitoring.
OLAP	Provision WAL, archive bandwidth, and recovery I/O for bulk-load peaks. Coordinate load pacing and checkpoints when reducing spikes; never break the recovery chain for throughput.
Small nodes	Start from safe defaults or the measured Pigsty value and set explicit alerts for limited disk capacity. Do not disable durability or break the recovery chain merely to save modest I/O.

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	`16MB`	different	`16MB`
OLAP	`16MB`	different	`16MB`
CRIT	`16MB`	different	`16MB`
TINY	`16MB`	different	`16MB`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 16MB (dcs); OLAP: PG9.0–19 Beta 3 = 16MB (dcs); CRIT: PG9.0–19 Beta 3 = 16MB (dcs); TINY: PG9.0–19 Beta 3 = 16MB (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to use the normal one-segment ceiling explicitly for burst absorption; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

Common pitfalls

Reading -1 as a negative allocation rather than automatic sizing.
Forgetting that the automatic choice is based on shared_buffers and capped at one WAL segment.
Reading an unqualified positive value as bytes rather than WAL blocks; very small positives are raised to the minimum.
Allocating a large manual buffer without evidence of WALInsert/WALWrite pressure.
Expecting more WAL buffers to replace durable flushes or improve a storage-bound WALSync path.

fsync · full_page_writes · wal_sync_method · synchronous_commit · wal_writer_delay · wal_writer_flush_after