Wiki / Configuration Parameters

When this parameter is on, the PostgreSQL server writes the entire content of each disk page to WAL during the first modification of that page after a checkpoint. This is needed because a page write that is in process during an operating system crash might be only partially completed, leading to an on-disk page that contains a mix of old and new data. The row-level change data normally stored in WAL will not be enough to completely restore such a page during post-crash recovery. Storing the full page image guarantees that the page can be correctly restored, but at the price of increasing the amount of data that must be written to WAL. (Because WAL replay always starts from a checkpoint, it is sufficient to do this during the first change of each page after a checkpoint. Therefore, one way to reduce the cost of full-page writes is to increase the checkpoint interval parameters.) Turning this parameter off speeds normal operation, but might lead to either unrecoverable data corruption, or silent data corruption, after a system failure. The risks are similar to turning off fsync, though smaller, and it should be turned off only based on the same circumstances recommended for that parameter. Turning off this parameter does not affect use of WAL archiving for point-in-time recovery (PITR) (see Section 25.3). This parameter can only be set in the postgresql.conf file or on the server command line. The default is on.

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

boot val

on

category

Write-Ahead Log / Settings

context

sighup

documented

true

enumvals

Unknown

lang

en

max val

Unknown

metadata version

18

min val

Unknown

name

full_page_writes

short desc

Writes full pages to WAL when first modified after a checkpoint.

source

pg-settings-source-snapshot

unit

Unknown

vartype

bool

A page write in process during an operating system crash might be only partially written to disk.  During recovery, the row changes stored in WAL are not enough to recover.  This option writes pages when first modified after a checkpoint to WAL so full recovery is possible.