wal_sync_method

wal_sync_method — Selects the method used for forcing WAL updates to disk. Observed in PG9.0–19 Beta 3; its last measured boot default is fdatasync in PG19 Beta 3, with sighup context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Selects the method used for forcing WAL updates to disk.”

Identity

Type , Valueenum: Upstream pg_settings type
Context , Valuesighup: Takes effect after configuration reload
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Valuefsync, fdatasync, open_sync, open_datasync: — for non-enum types
Category , ValueWrite-Ahead Log / Settings: Upstream classification
Latest boot value , Valuefdatasync: fdatasync

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	`fdatasync`	—	fdatasync

How it works

Selects the method used for forcing WAL updates to disk. A configuration reload applies a new value; existing work already in flight is not retroactively changed.

This chooses the operating-system primitive used to force WAL to durable storage, such as fdatasync, fsync, or open-sync variants. Availability and performance are platform/filesystem specific; all supported choices preserve the durability contract when the stack is honest.

Monitor and change wal_sync_method together with fsync, full_page_writes, synchronous_commit. Validate on the relevant server role and real workload, then use its sighup 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_sync_method 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	Unmodified	—	—
OLAP	Unmodified	—	—
CRIT	Unmodified	—	—
TINY	Unmodified	—	—

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 unmodified; OLAP: PG9.0–19 Beta 3 unmodified; CRIT: PG9.0–19 Beta 3 unmodified; TINY: PG9.0–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Selecting a method that the operating system or filesystem does not support.
Benchmarking on a different kernel, mount option, or storage cache than production.
Confusing write throughput with durable-sync latency.
Changing the method without a crash/power-loss durability test.
Assuming the fastest method on data files is also the best method for WAL.

fsync · full_page_writes · synchronous_commit · wal_buffers · wal_writer_delay · commit_delay