Change hot_standby default value to 'on'

This goes together with the changes made to enable replication on the
sending side by default (wal_level, max_wal_senders etc) by making the
receiving stadby node also enable it by default.

Huong Dangminh

doc/src/sgml/config.sgml

@@ -3227,7 +3227,7 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
        <para>
         Specifies whether or not you can connect and run queries during
         recovery, as described in <xref linkend="hot-standby">.
-        The default value is <literal>off</literal>.
+        The default value is <literal>on</literal>.
         This parameter can only be set at server start. It only has effect
         during archive recovery or in standby mode.
        </para>

doc/src/sgml/high-availability.sgml

@@ -2057,8 +2057,8 @@ if (!triggered)
    <title>Administrator's Overview</title>
 
    <para>
-    If <varname>hot_standby</> is turned <literal>on</> in
-    <filename>postgresql.conf</> and there is a <filename>recovery.conf</>
+    If <varname>hot_standby</> is <literal>on</> in <filename>postgresql.conf</>
+    (the default value) and there is a <filename>recovery.conf</>
     file present, the server will run in Hot Standby mode.
     However, it may take some time for Hot Standby connections to be allowed,
     because the server will not accept connections until it has completed

src/backend/utils/misc/guc.c

@@ -1571,7 +1571,7 @@ static struct config_bool ConfigureNamesBool[] =
 			NULL
 		},
 		&EnableHotStandby,
-		false,
+		true,
 		NULL, NULL, NULL
 	},
 

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

@@ -254,7 +254,7 @@
 
 # These settings are ignored on a master server.
 
-#hot_standby = off			# "on" allows queries during recovery
+#hot_standby = on			# "off" disallows queries during recovery
 					# (change requires restart)
 #max_standby_archive_delay = 30s	# max delay before canceling queries
 					# when reading WAL from archive;