PostgreSQL 13: support "wal_keep_size"

Renamed from "wal_keep_segments" in core commit f5dff459.

doc/cloning-standbys.xml

@@ -46,6 +46,7 @@
       <para>
        WAL management on the primary becomes much easier as there's no need
        to use replication slots, and <varname>wal_keep_segments</varname>
+       (PostgreSQL 13 and later: <varname>wal_keep_size</varname>)
        does not need to be set.
      </para>
     </listitem>
@@ -234,7 +235,8 @@ description = "Main cluster"
     that any standby connected to the primary using a replication slot will always
     be able to retrieve the required WAL files. This removes the need to manually
     manage WAL file retention by estimating the number of WAL files that need to
-    be maintained on the primary using <varname>wal_keep_segments</varname>.
+    be maintained on the primary using <varname>wal_keep_segments</varname>
+    (PostgreSQL 13 and later: <varname>wal_keep_size</varname>).
     Do however be aware that if a standby is disconnected, WAL will continue to
     accumulate on the primary until either the standby reconnects or the replication
     slot is dropped.

doc/configuration.xml

@@ -270,7 +270,7 @@
 
       <varlistentry>
 
-        <term><option>wal_keep_segments</option></term>
+        <term><option>wal_keep_segments</option> / <option>wal_keep_size</option></term>
 
         <listitem>
 
@@ -279,25 +279,36 @@
             <secondary>PostgreSQL configuration</secondary>
           </indexterm>
 
+
+          <indexterm>
+            <primary>wal_keep_size</primary>
+            <secondary>PostgreSQL configuration</secondary>
+          </indexterm>
+
           <para>
-            Normally there is no need to set <option>wal_keep_segments</option> (default: <literal>0</literal>), as it
-            is <emphasis>not</emphasis> a reliable way of ensuring that all required WAL segments are available to standbys.
-            Replication slots and/or an archiving solution such as Barman are recommended to ensure standbys have a reliable
+            Normally there is no need to set <option>wal_keep_segments</option>
+            (PostgreSQL 13 and later: <varname>wal_keep_size</varname>; default: <literal>0</literal>),
+            as it is <emphasis>not</emphasis> a reliable way of ensuring that all required WAL
+            segments are available to standbys. Replication slots and/or an archiving solution
+            such as Barman are recommended to ensure standbys have a reliable
             source of WAL segments at all times.
           </para>
           <para>
-            The only reason ever to set  <option>wal_keep_segments</option> is you have
-            you have configured <option>pg_basebackup_options</option>
+            The only reason ever to set  <option>wal_keep_segments</option> / <option>wal_keep_size</option>
+            is you have you have configured <option>pg_basebackup_options</option>
             in <filename>repmgr.conf</filename> to include the setting <literal>--wal-method=fetch</literal>
             (PostgreSQL 9.6 and earlier: <literal>--xlog-method=fetch</literal>)
             <emphasis>and</emphasis> you have <emphasis>not</emphasis> set <option>restore_command</option>
             in <filename>repmgr.conf</filename> to fetch WAL files from a reliable source such as Barman,
             in which case you'll need to set <option>wal_keep_segments</option>
             to a sufficiently high number to ensure that all WAL files required by the standby
-            are retained. However we do not recommend managing replication in this way.
+            are retained. However we do not recommend WAL retention in this way.
           </para>
           <para>
             PostgreSQL documentation: <ulink url="https://www.postgresql.org/docs/current/runtime-config-replication.html#GUC-WAL-KEEP-SEGMENTS">wal_keep_segments</ulink>.
+            <!--
+             PostgreSQL documentation: <ulink url="https://www.postgresql.org/docs/current/runtime-config-replication.html#GUC-WAL-KEEP-SIZE">wal_keep_size</ulink>.
+              -->
           </para>
         </listitem>
       </varlistentry>

doc/repmgr-standby-clone.xml

@@ -175,7 +175,10 @@
     <programlisting>
       pg_basebackup_options='--wal-method=fetch'</programlisting>
 
-    and ensure that <literal>wal_keep_segments</literal> is set to an appropriately high value.
+    and ensure that <literal>wal_keep_segments</literal> (PostgreSQL 13 and later:
+    <literal>wal_keep_size</literal>) is set to an appropriately high value. Note
+    however that this is not a particularly reliable way of ensuring sufficient
+    WAL is retained and is not recommended.
     See the <ulink url="https://www.postgresql.org/docs/current/app-pgbasebackup.html">
     pg_basebackup</ulink> documentation for details.
    </para>