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 03421b94e589e3d294259ab9b7afac7e29238152..bda239e08055c65f204def7647a70cbb2819a772 100644 (file)
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3187,6 +3187,7 @@ 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 df65dfc76d13c7fb9afb472be209eb5002470e3a..7705dbc181e7a0698265e2f456e2cd083e918051 100644 (file)
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -220,7 +220,7 @@
 #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