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doc: Improve description of wal_compression

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The description of this GUC provides a list of the situations where
full-page writes are generated.  However, it is not completely exact,
mentioning only the cases where full_page_writes=on or base backups.  It
is possible to generate full-page writes in more situations than these
two, making the description confusing as it implies that no other cases
exist.

The description is slightly reworded to take into account that other
cases are possible, without mentioning them directly to minimize the
maintenance burden should FPWs be generated in more contexts in the
future.

Author: Jingtang Zhang <mrdrivingduck@gmail.com>
Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru>
Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
Discussion: https://postgr.es/m/CAPsk3_CtAYa_fy4p6=x7qtoutrdKvg1kGk46D5fsE=sMt2546g@mail.gmail.com
Backpatch-through: 13
This commit is contained in:
Michael Paquier
2025-08-21 13:25:03 +09:00
parent a67d4847a4
commit b5d87a823f
1 changed files with 3 additions and 2 deletions
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doc/src/sgml/config.sgml
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@@ -3399,8 +3399,9 @@ include_dir 'conf.d'
This parameter enables compression of WAL using the specified This parameter enables compression of WAL using the specified
compression method. compression method.
When enabled, the <productname>PostgreSQL</productname> When enabled, the <productname>PostgreSQL</productname>
server compresses full page images written to WAL when server compresses full page images written to WAL (e.g. when
<xref linkend="guc-full-page-writes"/> is on or during a base backup. <xref linkend="guc-full-page-writes"/> is on, during a base backup,
etc.).
A compressed page image will be decompressed during WAL replay. A compressed page image will be decompressed during WAL replay.
The supported methods are <literal>pglz</literal>, The supported methods are <literal>pglz</literal>,
<literal>lz4</literal> (if <productname>PostgreSQL</productname> <literal>lz4</literal> (if <productname>PostgreSQL</productname>