From 89084e17df13823077bad2f6ad4c1cb0e095ccc4 Mon Sep 17 00:00:00 2001
From: Euler Taveira <euler@eulerto.com>
Date: Wed, 26 Nov 2025 12:40:43 -0300
Subject: [PATCH v1] Change default_toast_compression to lz4

The default value for default_toast_compression was pglz. The main
reason is that this option is always available. However, it is known
that pglz uses more CPU than lz4. The default value will be lz4 if lz4
support is built, otherwise, pglz.
---
 doc/src/sgml/config.sgml                      | 3 ++-
 src/backend/access/common/toast_compression.c | 2 +-
 src/backend/utils/misc/guc_parameters.dat     | 2 +-
 src/bin/initdb/initdb.c                       | 5 +++++
 src/include/access/toast_compression.h        | 9 +++++++++
 5 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 737b90736bf..c063f013e2f 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -9910,7 +9910,8 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         The supported compression methods are <literal>pglz</literal> and
         (if <productname>PostgreSQL</productname> was compiled with
         <option>--with-lz4</option>) <literal>lz4</literal>.
-        The default is <literal>pglz</literal>.
+        The default is <literal>lz4</literal> (if available); otherwise,
+        <literal>pglz</literal>.
        </para>
       </listitem>
      </varlistentry>
diff --git a/src/backend/access/common/toast_compression.c b/src/backend/access/common/toast_compression.c
index 926f1e4008a..4bb29665eab 100644
--- a/src/backend/access/common/toast_compression.c
+++ b/src/backend/access/common/toast_compression.c
@@ -23,7 +23,7 @@
 #include "varatt.h"
 
 /* GUC */
-int			default_toast_compression = TOAST_PGLZ_COMPRESSION;
+int			default_toast_compression = DEFAULT_TOAST_COMPRESSION;
 
 #define NO_COMPRESSION_SUPPORT(method) \
 	ereport(ERROR, \
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index 3b9d8349078..cbe9bf055b3 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -735,7 +735,7 @@
 { name => 'default_toast_compression', type => 'enum', context => 'PGC_USERSET', group => 'CLIENT_CONN_STATEMENT',
   short_desc => 'Sets the default compression method for compressible values.',
   variable => 'default_toast_compression',
-  boot_val => 'TOAST_PGLZ_COMPRESSION',
+  boot_val => 'DEFAULT_TOAST_COMPRESSION',
   options => 'default_toast_compression_options',
 },
 
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 92fe2f531f7..92b120d8ab8 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -1424,6 +1424,11 @@ setup_config(void)
 									  "0640", false);
 	}
 
+#if USE_LZ4
+	conflines = replace_guc_value(conflines, "default_toast_compression",
+								  "lz4", true);
+#endif
+
 	/*
 	 * Now replace anything that's overridden via -c switches.
 	 */
diff --git a/src/include/access/toast_compression.h b/src/include/access/toast_compression.h
index 13c4612ceed..7526ea50c5a 100644
--- a/src/include/access/toast_compression.h
+++ b/src/include/access/toast_compression.h
@@ -52,6 +52,15 @@ typedef enum ToastCompressionId
 
 #define CompressionMethodIsValid(cm)  ((cm) != InvalidCompressionMethod)
 
+/*
+ * Choose an appropriate default toast compression method. If lz4 is
+ * compiled-in, use it, otherwise, use pglz.
+ */
+#ifdef USE_LZ4
+#define DEFAULT_TOAST_COMPRESSION	TOAST_LZ4_COMPRESSION
+#else
+#define DEFAULT_TOAST_COMPRESSION	TOAST_PGLZ_COMPRESSION
+#endif
 
 /* pglz compression/decompression routines */
 extern struct varlena *pglz_compress_datum(const struct varlena *value);
-- 
2.39.5