From: John Naylor <john.naylor@postgresql.org>
Date: Wed, 1 Jul 2026 01:50:08 +0000 (+0700)
Subject: Document wal_compression=on
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=8db58ac8eec7402af1a746621fb2910f1673db0a;p=thirdparty%2Fpostgresql.git

Document wal_compression=on

Commit 4035cd5d4 added LZ4 compression for full-page writes in WAL, and
retained "on" as a backward-compatible way to specify the builtin PGLZ
method. Document this meaning of "on" and update postgresql.conf.sample
to make the equivalence clear.

Author: Christoph Berg <myon@debian.org>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/akJDHRtXwGLTppsQ@msg.df7cb.de
Backpatch-through: 15
---

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 6a0bb6d1344..c691f055b68 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3671,6 +3671,7 @@ include_dir 'conf.d'
         was compiled with <option>--with-lz4</option>) and
         <literal>zstd</literal> (if <productname>PostgreSQL</productname>
         was compiled with <option>--with-zstd</option>).
+        The value <literal>on</literal> is a historical spelling of <literal>pglz</literal>.
         The default value is <literal>off</literal>.
         Only superusers and users with the appropriate <literal>SET</literal>
         privilege can change this setting.
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index ac38cddaaf9..86f2e16eba0 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -262,7 +262,7 @@
 #wal_log_hints = off                    # also do full page writes of non-critical updates
                                         # (change requires restart)
 #wal_compression = off                  # enables compression of full-page writes;
-                                        # off, pglz, lz4, zstd, or on
+                                        # off, pglz (or "on"), lz4, or zstd
 #wal_init_zero = on                     # zero-fill new WAL files
 #wal_recycle = on                       # recycle WAL files
 #wal_buffers = -1                       # min 32kB, -1 sets based on shared_buffers