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Date: Tue, 30 Jun 2026 12:19:21 +0200
From: Christoph Berg <myon@debian.org>
To: John Naylor <johncnaylorls@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>,
	Michael Paquier <michael@paquier.xyz>
Subject: Re: [PATCH] Document wal_compression=on
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Re: To John Naylor
> Or perhaps leave the door open for picking a better default in the future?
> 
>      The value <literal>on</literal> is currently an alias for <literal>pglz</literal>.

> Maybe we should also update the postgresql.conf.sample:

I'm attaching v2 that implements this (without the "currently").

Christoph

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	filename=v2-0001-Document-wal_compression-on.patch

From 7aefb8d5d2d650710a4462fdad2e926035344bd0 Mon Sep 17 00:00:00 2001
From: Christoph Berg <myon@debian.org>
Date: Mon, 29 Jun 2026 11:58:44 +0200
Subject: [PATCH v2] Document wal_compression=on

This was not included when lz4 support was added in
4035cd5d4eee4dae797bfc77ab07f8dcd8781b41, but since the value is still
legal and even mentioned in postgresql.conf.sample, it should be
documented.

Update postgresql.conf.sample to say "on" is the same as pglz.
---
 doc/src/sgml/config.sgml                      | 1 +
 src/backend/utils/misc/postgresql.conf.sample | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 569fc0e7dba..7bdc85539ce 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 an alias for <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
-- 
2.53.0


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