wal_segment_size

wal_segment_size — Shows the size of write ahead log segments. Observed in PG9.0–19 Beta 3; its last measured boot default is 16 MiB in PG19 Beta 3, with internal context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Shows the size of write ahead log segments.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valueinternal: Internal/preset and not user-settable
Unit , ValueB: Raw unit
Range , Value1048576 – 1073741824: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValuePreset Options: Upstream classification
Latest boot value , Value16777216: 16 MiB

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
PG9.0–10	`2048`	`8kB`	16 MiB (2048 × 8kB)
PG11–19 Beta 3	`16777216`	`B`	16 MiB

How it works

Shows the size of write ahead log segments. It is read-only and cannot be changed with SET or configuration-file edits.

It reports the WAL segment size. PostgreSQL 11 and later choose it at initdb time; older clusters normally inherit the build-time value.

Interpret it with min_wal_size, max_wal_size, wal_keep_size. Applications and operations tooling may read wal_segment_size for capability or environment detection, but cannot SET it; cross-cluster comparisons must account for build, initdb, and current-database differences.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Not tunable. Record wal_segment_size as a deployment/capability fact; if it is unexpected, fix the binary, initdb, or database-creation process rather than trying SET.
OLAP	Not tunable. Use wal_segment_size to verify format, build, or resource assumptions on analytical nodes and keep every read/write candidate compatible.
Small nodes	Not tunable. Preserve it in inventory and incident reports; do not custom-build or rebuild merely to change it without a demonstrated compatibility need.

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

Trying to change read-only wal_segment_size with SET or a configuration file.
Assuming every cluster, database, or vendor build reports the same value.
Ignoring the value in file-format or feature-compatibility checks.
Treating reported metadata as a performance target instead of an environment fact.

min_wal_size · max_wal_size · wal_keep_size · checkpoint_timeout · checkpoint_completion_target · wal_keep_segments