Change default value of default_toast_compression to "lz4", when available

The default value for default_toast_compression was "pglz".  The main
reason for this choice is that this option is always available, pglz
code being embedded in Postgres.  However, it is known that LZ4 is more
efficient than pglz: less CPU required, more compression on average.  As
of this commit, the default value of default_toast_compression becomes
"lz4", if available.  By switching to LZ4 as the default, users should
see natural speedups on TOAST data reads and/or writes.

Support for LZ4 in TOAST compression was added in Postgres v14, or 5
releases ago.  This should be long enough to consider this feature as
stable.

--with-lz4 is removed, replaced by a --without-lz4 to disable LZ4 in the
builds on an option-basis, following a practice similar to readline or
ICU.  References to --with-lz4 are removed from the documentation.

While at it, quotes are removed from default_toast_compression in
postgresql.conf.sample.  Quotes are not required in this case.  The
in-place value replacement done by initdb if the build supports LZ4
would not use them in the postgresql.conf file added to a
freshly-initialized cluster.

For the reference, a similar switch has been done with ICU in
fcb21b3acd.  Some of the changes done in this commit are consistent
with that.

Note: this is going to create some disturbance in the buildfarm, in
environments where lz4 is not installed.

Author: Euler Taveira <euler@eulerto.com>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Aleksander Alekseev <aleksander@tigerdata.com>
Discussion: https://posgr.es/m/435df33a-129e-4f0c-a803-f3935c5a5ecb@eisentraut.org

.cirrus.tasks.yml

@@ -984,6 +984,7 @@ task:
         --host=x86_64-w64-mingw32ucrt \
         --enable-cassert \
         --without-icu \
+        --without-lz4 \
         CC="ccache x86_64-w64-mingw32ucrt-gcc" \
         CXX="ccache x86_64-w64-mingw32ucrt-g++"
       make -s -j${BUILD_JOBS} clean

configure

@@ -1603,7 +1603,7 @@ Optional Packages:
   --with-system-tzdata=DIR
                           use system time zone data in DIR
   --without-zlib          do not use Zlib
-  --with-lz4              build with LZ4 support
+  --without-lz4           build without LZ4 support
   --with-zstd             build with ZSTD support
   --with-ssl=LIB          use LIB for SSL/TLS support (openssl)
   --with-openssl          obsolete spelling of --with-ssl=openssl
@@ -9570,7 +9570,9 @@ $as_echo "#define USE_LZ4 1" >>confdefs.h
   esac
 
 else
-  with_lz4=no
+  with_lz4=yes
+
+$as_echo "#define USE_LZ4 1" >>confdefs.h
 
 fi
 

configure.ac

@@ -1188,7 +1188,7 @@ AC_SUBST(with_zlib)
 # LZ4
 #
 AC_MSG_CHECKING([whether to build with LZ4 support])
-PGAC_ARG_BOOL(with, lz4, no, [build with LZ4 support],
+PGAC_ARG_BOOL(with, lz4, yes, [build without LZ4 support],
               [AC_DEFINE([USE_LZ4], 1, [Define to 1 to build with LZ4 support. (--with-lz4)])])
 AC_MSG_RESULT([$with_lz4])
 AC_SUBST(with_lz4)

doc/src/sgml/config.sgml

@@ -3498,10 +3498,9 @@ include_dir 'conf.d'
         etc.).
         A compressed page image will be decompressed during WAL replay.
         The supported methods are <literal>pglz</literal>,
-        <literal>lz4</literal> (if <productname>PostgreSQL</productname>
-        was compiled with <option>--with-lz4</option>) and
-        <literal>zstd</literal> (if <productname>PostgreSQL</productname>
-        was compiled with <option>--with-zstd</option>).
+        <literal>lz4</literal> and <literal>zstd</literal> (if
+        <productname>PostgreSQL</productname> was compiled with
+        <option>--with-zstd</option>).
         The default value is <literal>off</literal>.
         Only superusers and users with the appropriate <literal>SET</literal>
         privilege can change this setting.
@@ -10018,9 +10017,9 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         <command>CREATE TABLE</command> or
         <command>ALTER TABLE</command>.)
         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>.
+        <literal>lz4</literal>.
+        The default is <literal>lz4</literal> (if available); otherwise,
+        <literal>pglz</literal>.
        </para>
       </listitem>
      </varlistentry>

doc/src/sgml/installation.sgml

@@ -975,15 +975,6 @@ build-postgresql:
        </listitem>
       </varlistentry>
 
-      <varlistentry id="configure-option-with-lz4">
-       <term><option>--with-lz4</option></term>
-       <listitem>
-        <para>
-         Build with <productname>LZ4</productname> compression support.
-        </para>
-       </listitem>
-      </varlistentry>
-
       <varlistentry id="configure-option-with-zstd">
        <term><option>--with-zstd</option></term>
        <listitem>
@@ -1315,6 +1306,18 @@ build-postgresql:
        </listitem>
       </varlistentry>
 
+      <varlistentry id="configure-option-without-lz4">
+       <term><option>--without-lz4</option></term>
+       <listitem>
+        <para>
+         <indexterm>
+          <primary>lz4</primary>
+         </indexterm>
+         Prevents use of the <application>LZ4</application> library.
+        </para>
+       </listitem>
+      </varlistentry>
+
      </variablelist>
 
    </sect3>

doc/src/sgml/ref/alter_table.sgml

@@ -462,9 +462,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       its existing compression method, rather than being recompressed with the
       compression method of the target column.
       The supported compression
-      methods are <literal>pglz</literal> and <literal>lz4</literal>.
-      (<literal>lz4</literal> is available only if <option>--with-lz4</option>
-      was used when building <productname>PostgreSQL</productname>.)  In
+      methods are <literal>pglz</literal> and <literal>lz4</literal>.  In
       addition, <replaceable class="parameter">compression_method</replaceable>
       can be <literal>default</literal>, which selects the default behavior of
       consulting the <xref linkend="guc-default-toast-compression"/> setting

doc/src/sgml/ref/create_table.sgml

@@ -344,9 +344,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       has no direct effect, because such tables have no storage of their own,
       but the configured value will be inherited by newly-created partitions.
       The supported compression methods are <literal>pglz</literal> and
-      <literal>lz4</literal>.  (<literal>lz4</literal> is available only if
-      <option>--with-lz4</option> was used when building
-      <productname>PostgreSQL</productname>.)  In addition,
+      <literal>lz4</literal>.  In addition,
       <replaceable class="parameter">compression_method</replaceable>
       can be <literal>default</literal> to explicitly specify the default
       behavior, which is to consult the

doc/src/sgml/ref/pg_receivewal.sgml

@@ -275,9 +275,7 @@ PostgreSQL documentation
        </para>
        <para>
         The compression method can be set to <literal>gzip</literal>,
-        <literal>lz4</literal> (if <productname>PostgreSQL</productname>
-        was compiled with <option>--with-lz4</option>) or
-        <literal>none</literal> for no compression.
+        <literal>lz4</literal> or <literal>none</literal> for no compression.
         A compression detail string can optionally be specified.  If the
         detail string is an integer, it specifies the compression level.
         Otherwise, it should be a comma-separated list of items, each of the

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, \

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',
 },
 

src/backend/utils/misc/postgresql.conf.sample

@@ -779,7 +779,7 @@
 #row_security = on
 #default_table_access_method = 'heap'
 #default_tablespace = ''                # a tablespace name, '' uses the default
-#default_toast_compression = 'pglz'     # 'pglz' or 'lz4'
+#default_toast_compression = pglz       # pglz or lz4
 #temp_tablespaces = ''                  # a list of tablespace names, '' uses
                                         # only default tablespace
 #check_function_bodies = on

src/bin/initdb/initdb.c

@@ -1426,6 +1426,11 @@ 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.
 	 */

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 varlena *pglz_compress_datum(const varlena *value);