doc: Improve documentation discoverability for pgoutput.

Previously, the documentation for pgoutput was located in the section on
the logical streaming replication protocol, and there was no index entry
for it. As a result, users had difficulty finding information about pgoutput.

This commit moves the pgoutput documentation under the logical decoding
section and adds an index entry, making it easier for users to locate and
access this information.

Discussion: https://postgr.es/m/CAHGQGwFJTbygdhhjR_iP4Oem=Lo1xsptWWOq825uoW+hG_Lfnw@mail.gmail.com

Author: MasaoFujii

doc/src/sgml/logical-replication.sgml

@@ -542,8 +542,8 @@
     it manually before the subscription can be activated. The steps to create
     the slot and activate the subscription are shown in the following examples.
     These examples specify the standard logical decoding output plugin
-    (<literal>pgoutput</literal>), which is what the built-in logical
-    replication uses.
+    (<xref linkend="logicaldecoding-pgoutput"/>),
+    which is what the built-in logical replication uses.
    </para>
    <para>
     First, create a publication for the examples to use.
@@ -2173,8 +2173,8 @@ CONTEXT:  processing remote data for replication origin "pg_16395" during "INSER
    implemented by <literal>walsender</literal> and <literal>apply</literal>
    processes.  The walsender process starts logical decoding (described
    in <xref linkend="logicaldecoding"/>) of the WAL and loads the standard
-   logical decoding output plugin (<literal>pgoutput</literal>).  The plugin
-   transforms the changes read
+   logical decoding output plugin (<xref linkend="logicaldecoding-pgoutput"/>).
+   The plugin transforms the changes read
    from WAL to the logical replication protocol
    (see <xref linkend="protocol-logical-replication"/>) and filters the data
    according to the publication specification.  The data is then continuously

doc/src/sgml/logicaldecoding.sgml

@@ -574,6 +574,152 @@ DETAIL:  Synchronization could lead to data loss, because the remote slot needs
 
   <sect1 id="logicaldecoding-output-plugin">
    <title>Logical Decoding Output Plugins</title>
+
+   <para>
+    <productname>PostgreSQL</productname> provides two logical decoding
+    output plugins, <xref linkend="logicaldecoding-pgoutput"/> and
+    <xref linkend="test-decoding"/>.  You can also develop custom output plugins
+    (see <xref linkend="logicaldecoding-output-plugin-writing"/> for details).
+   </para>
+
+   <sect2 id="logicaldecoding-pgoutput" xreflabel="pgoutput">
+    <title>pgoutput &mdash; Standard Logical Decoding Output Plugin</title>
+
+    <indexterm zone="logicaldecoding-pgoutput">
+     <primary>pgoutput</primary>
+    </indexterm>
+
+    <para>
+     <filename>pgoutput</filename> is the standard logical decoding output
+     plugin provided by <productname>PostgreSQL</productname>.
+     It's used for the built-in <link linkend="logical-replication">
+     logical replication</link>.
+    </para>
+
+    <sect3 id="logicaldecoding-pgoutput-options">
+     <title>Options</title>
+
+     <variablelist>
+      <varlistentry>
+       <term>
+        proto_version
+       </term>
+       <listitem>
+        <para>
+         Protocol version. Currently versions <literal>1</literal>, <literal>2</literal>,
+         <literal>3</literal>, and <literal>4</literal> are supported.  A valid
+         version is required.
+        </para>
+        <para>
+         Version <literal>2</literal> is supported only for server version 14
+         and above, and it allows streaming of large in-progress transactions.
+        </para>
+        <para>
+         Version <literal>3</literal> is supported only for server version 15
+         and above, and it allows streaming of two-phase commits.
+        </para>
+        <para>
+         Version <literal>4</literal> is supported only for server version 16
+         and above, and it allows streams of large in-progress transactions to
+         be applied in parallel.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+        publication_names
+       </term>
+       <listitem>
+        <para>
+         Comma-separated list of publication names for which to subscribe
+         (receive changes). The individual publication names are treated
+         as standard objects names and can be quoted the same as needed.
+         At least one publication name is required.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+        binary
+       </term>
+       <listitem>
+        <para>
+         Boolean option to use binary transfer mode.  Binary mode is faster
+         than the text mode but slightly less robust.
+         The default is <literal>off</literal>.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+        messages
+       </term>
+       <listitem>
+        <para>
+         Boolean option to enable sending the messages that are written
+         by <function>pg_logical_emit_message</function>.
+         The default is <literal>off</literal>.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+        streaming
+       </term>
+       <listitem>
+        <para>
+         Option to enable streaming of in-progress transactions. Valid values are
+         <literal>off</literal> (the default), <literal>on</literal> and
+         <literal>parallel</literal>. The setting <literal>parallel</literal>
+         enables sending extra information with some messages to be used for
+         parallelization. Minimum protocol version 2 is required to turn it
+         <literal>on</literal>.  Minimum protocol version 4 is required for the
+         <literal>parallel</literal> value.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+        two_phase
+       </term>
+       <listitem>
+        <para>
+         Boolean option to enable two-phase transactions.   Minimum protocol
+         version 3 is required to turn it on.
+         The default is <literal>off</literal>.
+        </para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+        origin
+       </term>
+       <listitem>
+        <para>
+         Option to send changes by their origin.  Possible values are
+         <literal>none</literal> to only send the changes that have no origin
+         associated, or <literal>any</literal>
+         to send the changes regardless of their origin.  This can be used
+         to avoid loops (infinite replication of the same data) among
+         replication nodes.
+         The default is <literal>any</literal>.
+        </para>
+       </listitem>
+      </varlistentry>
+     </variablelist>
+
+    </sect3>
+   </sect2>
+  </sect1>
+
+  <sect1 id="logicaldecoding-output-plugin-writing">
+   <title>Writing Logical Decoding Output Plugins</title>
    <para>
     An example output plugin can be found in the
     <link linkend="test-decoding">

doc/src/sgml/protocol.sgml

@@ -2955,7 +2955,7 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
         <listitem>
          <para>
           The name of an option passed to the slot's logical decoding output
-          plugin.  See <xref linkend="protocol-logical-replication"/> for
+          plugin.  See <xref linkend="logicaldecoding-pgoutput-options"/> for
           options that are accepted by the standard (<literal>pgoutput</literal>)
           plugin.
          </para>
@@ -3523,134 +3523,15 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
   the physical streaming replication protocol.
  </para>
 
- <para>
-  <productname>PostgreSQL</productname> logical decoding supports output
-  plugins.  <literal>pgoutput</literal> is the standard one used for
-  the built-in logical replication.
- </para>
-
  <sect2 id="protocol-logical-replication-params">
   <title>Logical Streaming Replication Parameters</title>
 
   <para>
-   Using the <literal>START_REPLICATION</literal> command,
-   <literal>pgoutput</literal> accepts the following options:
-
-   <variablelist>
-    <varlistentry>
-     <term>
-      proto_version
-     </term>
-     <listitem>
-      <para>
-       Protocol version. Currently versions <literal>1</literal>, <literal>2</literal>,
-       <literal>3</literal>, and <literal>4</literal> are supported.  A valid
-       version is required.
-      </para>
-      <para>
-       Version <literal>2</literal> is supported only for server version 14
-       and above, and it allows streaming of large in-progress transactions.
-      </para>
-      <para>
-       Version <literal>3</literal> is supported only for server version 15
-       and above, and it allows streaming of two-phase commits.
-      </para>
-      <para>
-       Version <literal>4</literal> is supported only for server version 16
-       and above, and it allows streams of large in-progress transactions to
-       be applied in parallel.
-      </para>
-     </listitem>
-    </varlistentry>
-
-    <varlistentry>
-     <term>
-      publication_names
-     </term>
-     <listitem>
-      <para>
-       Comma-separated list of publication names for which to subscribe
-       (receive changes). The individual publication names are treated
-       as standard objects names and can be quoted the same as needed.
-       At least one publication name is required.
-      </para>
-     </listitem>
-    </varlistentry>
-
-    <varlistentry>
-     <term>
-      binary
-     </term>
-     <listitem>
-      <para>
-       Boolean option to use binary transfer mode.  Binary mode is faster
-       than the text mode but slightly less robust.
-       The default is <literal>off</literal>.
-      </para>
-     </listitem>
-    </varlistentry>
-
-    <varlistentry>
-     <term>
-      messages
-     </term>
-     <listitem>
-      <para>
-       Boolean option to enable sending the messages that are written
-       by <function>pg_logical_emit_message</function>.
-       The default is <literal>off</literal>.
-      </para>
-     </listitem>
-    </varlistentry>
-
-    <varlistentry>
-     <term>
-      streaming
-     </term>
-     <listitem>
-      <para>
-       Option to enable streaming of in-progress transactions. Valid values are
-       <literal>off</literal> (the default), <literal>on</literal> and
-       <literal>parallel</literal>. The setting <literal>parallel</literal>
-       enables sending extra information with some messages to be used for
-       parallelization. Minimum protocol version 2 is required to turn it
-       <literal>on</literal>.  Minimum protocol version 4 is required for the
-       <literal>parallel</literal> value.
-      </para>
-     </listitem>
-    </varlistentry>
-
-    <varlistentry>
-     <term>
-      two_phase
-     </term>
-     <listitem>
-      <para>
-       Boolean option to enable two-phase transactions.   Minimum protocol
-       version 3 is required to turn it on.
-       The default is <literal>off</literal>.
-      </para>
-     </listitem>
-    </varlistentry>
-
-    <varlistentry>
-     <term>
-      origin
-     </term>
-     <listitem>
-      <para>
-       Option to send changes by their origin.  Possible values are
-       <literal>none</literal> to only send the changes that have no origin
-       associated, or <literal>any</literal>
-       to send the changes regardless of their origin.  This can be used
-       to avoid loops (infinite replication of the same data) among
-       replication nodes.
-       The default is <literal>any</literal>.
-      </para>
-     </listitem>
-    </varlistentry>
-   </variablelist>
-
+   The <literal>START_REPLICATION</literal> command can pass
+   options to the logical decoding output plugin associated
+   with the specified replication slot.
+   See <xref linkend="logicaldecoding-pgoutput-options"/> for options
+   that are accepted by the standard (<literal>pgoutput</literal>) plugin.
   </para>
  </sect2>