Wiki / Configuration Parameters

The amount of shared memory used for WAL data that has not yet been written to disk. The default setting of -1 selects a size equal to 1/32nd (about 3%) of shared_buffers, but not less than 64kB nor more than the size of one WAL segment, typically 16MB. This value can be set manually if the automatic choice is too large or too small, but any positive value less than 32kB will be treated as 32kB. If this value is specified without units, it is taken as WAL blocks, that is XLOG_BLCKSZ bytes, typically 8kB. This parameter can only be set at server start. The contents of the WAL buffers are written out to disk at every transaction commit, so extremely large values are unlikely to provide a significant benefit. However, setting this value to at least a few megabytes can improve write performance on a busy server where many clients are committing at once. The auto-tuning selected by the default setting of -1 should give reasonable results in most cases.

English manual coverage begins with PostgreSQL 7.4. Source history and runtime observations have their own recorded version boundaries.

boot val

-1

category

Write-Ahead Log / Settings

context

postmaster

documented

true

enumvals

Unknown

extra desc

-1 means use a fraction of "shared_buffers".

lang

en

max val

262143

metadata version

18

min val

-1

name

wal_buffers

short desc

Sets the number of disk-page buffers in shared memory for WAL.

source

pg-settings-source-snapshot

unit

8kB

vartype

integer