Change default of recovery_target_timeline to 'latest'

This is what one usually wants for recovery and almost always wants
for a standby.

Discussion: https://www.postgresql.org/message-id/flat/6dd2c23a-4162-8469-410f-bfe146e28c0c@2ndquadrant.com/Reviewed-by: David Steele <david@pgmasters.net>
Reviewed-by: Michael Paquier <michael@paquier.xyz>

doc/src/sgml/config.sgml

@@ -3353,10 +3353,14 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
         Specifies recovering into a particular timeline.  The value can be a
         numeric timeline ID or a special value.  The value
         <literal>current</literal> recovers along the same timeline that was
-        current when the base backup was taken.  That is the default.  The
+        current when the base backup was taken.  The
         value <literal>latest</literal> recovers
         to the latest timeline found in the archive, which is useful in
-        a standby server. Other than that you only need to set this parameter
+        a standby server.  <literal>latest</literal> is the default.
+       </para>
+
+       <para>
+        You usually only need to set this parameter
         in complex re-recovery situations, where you need to return to
         a state that itself was reached after a point-in-time recovery.
         See <xref linkend="backup-timelines"/> for discussion.

doc/src/sgml/high-availability.sgml

@@ -690,8 +690,8 @@ protocol to make nodes agree on a serializable transactional order.
     <filename>standby.signal</filename> in the standby's cluster data
     directory. Set <xref linkend="guc-restore-command"/> to a simple command to copy files from
     the WAL archive. If you plan to have multiple standby servers for high
-    availability purposes, set <varname>recovery_target_timeline</varname> to
-    <literal>latest</literal>, to make the standby server follow the timeline change
+    availability purposes, make sure that <varname>recovery_target_timeline</varname> is set to
+    <literal>latest</literal> (the default), to make the standby server follow the timeline change
     that occurs at failover to another standby.
    </para>
 
@@ -1024,7 +1024,7 @@ primary_slot_name = 'node_a_slot'
    <para>
     If an upstream standby server is promoted to become new master, downstream
     servers will continue to stream from the new master if
-    <varname>recovery_target_timeline</varname> is set to <literal>'latest'</literal>.
+    <varname>recovery_target_timeline</varname> is set to <literal>'latest'</literal> (the default).
    </para>
 
    <para>

src/backend/access/transam/xlog.c

@@ -324,7 +324,7 @@ static bool recoveryStopAfter;
  * file was created.)  During a sequential scan we do not allow this value
  * to decrease.
  */
-RecoveryTargetTimeLineGoal recoveryTargetTimeLineGoal = RECOVERY_TARGET_TIMELINE_CONTROLFILE;
+RecoveryTargetTimeLineGoal recoveryTargetTimeLineGoal = RECOVERY_TARGET_TIMELINE_LATEST;
 TimeLineID	recoveryTargetTLIRequested = 0;
 TimeLineID	recoveryTargetTLI = 0;
 static List *expectedTLEs;

src/backend/utils/misc/guc.c

@@ -3387,7 +3387,7 @@ static struct config_string ConfigureNamesString[] =
 			NULL
 		},
 		&recovery_target_timeline_string,
-		"current",
+		"latest",
 		check_recovery_target_timeline, assign_recovery_target_timeline, NULL
 	},
 
@@ -11028,7 +11028,7 @@ show_data_directory_mode(void)
 static bool
 check_recovery_target_timeline(char **newval, void **extra, GucSource source)
 {
-	RecoveryTargetTimeLineGoal rttg = RECOVERY_TARGET_TIMELINE_CONTROLFILE;
+	RecoveryTargetTimeLineGoal rttg;
 	RecoveryTargetTimeLineGoal *myextra;
 
 	if (strcmp(*newval, "current") == 0)
@@ -11037,6 +11037,8 @@ check_recovery_target_timeline(char **newval, void **extra, GucSource source)
 		rttg = RECOVERY_TARGET_TIMELINE_LATEST;
 	else
 	{
+		rttg = RECOVERY_TARGET_TIMELINE_NUMERIC;
+
 		errno = 0;
 		strtoul(*newval, NULL, 0);
 		if (errno == EINVAL || errno == ERANGE)
@@ -11044,7 +11046,6 @@ check_recovery_target_timeline(char **newval, void **extra, GucSource source)
 			GUC_check_errdetail("recovery_target_timeline is not a valid number.");
 			return false;
 		}
-		rttg = RECOVERY_TARGET_TIMELINE_NUMERIC;
 	}
 
 	myextra = (RecoveryTargetTimeLineGoal *) guc_malloc(ERROR, sizeof(RecoveryTargetTimeLineGoal));

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

@@ -261,7 +261,7 @@
 				# just after the specified recovery target (on)
 				# just before the recovery target (off)
 				# (change requires restart)
-#recovery_target_timeline = 'current'	# 'current', 'latest', or timeline ID
+#recovery_target_timeline = 'latest'	# 'current', 'latest', or timeline ID
 				# (change requires restart)
 #recovery_target_action = 'pause'	# 'pause', 'promote', 'shutdown'
 				# (change requires restart)

src/bin/pg_rewind/RewindTest.pm

@@ -161,7 +161,6 @@ sub create_standby
 	$node_standby->append_conf(
 		"postgresql.conf", qq(
 primary_conninfo='$connstr_master application_name=rewind_standby'
-recovery_target_timeline='latest'
 ));
 
 	$node_standby->set_standby_mode();
@@ -273,7 +272,6 @@ sub run_pg_rewind
 	$node_master->append_conf(
 		'postgresql.conf', qq(
 primary_conninfo='port=$port_standby'
-recovery_target_timeline='latest'
 ));
 
 	$node_master->set_standby_mode();

src/test/recovery/t/004_timeline_switch.pl

@@ -51,7 +51,6 @@ my $connstr_1 = $node_standby_1->connstr;
 $node_standby_2->append_conf(
 	'postgresql.conf', qq(
 primary_conninfo='$connstr_1 application_name=@{[$node_standby_2->name]}'
-recovery_target_timeline='latest'
 ));
 $node_standby_2->restart;
 

src/test/recovery/t/009_twophase.pl

@@ -229,10 +229,6 @@ is($psql_rc, '0', "Restore of prepared transaction on promoted standby");
 
 # restart old master as new standby
 $cur_standby->enable_streaming($cur_master);
-$cur_standby->append_conf(
-	'postgresql.conf', qq(
-recovery_target_timeline='latest'
-));
 $cur_standby->start;
 
 ###############################################################################
@@ -267,10 +263,6 @@ is($psql_out, '1',
 
 # restart old master as new standby
 $cur_standby->enable_streaming($cur_master);
-$cur_standby->append_conf(
-	'postgresql.conf', qq(
-recovery_target_timeline='latest'
-));
 $cur_standby->start;
 
 $cur_master->psql('postgres', "COMMIT PREPARED 'xact_009_11'");
@@ -307,10 +299,6 @@ is($psql_out, '1',
 
 # restart old master as new standby
 $cur_standby->enable_streaming($cur_master);
-$cur_standby->append_conf(
-	'postgresql.conf', qq(
-recovery_target_timeline='latest'
-));
 $cur_standby->start;
 
 $cur_master->psql('postgres', "COMMIT PREPARED 'xact_009_12'");

src/test/recovery/t/012_subtransactions.pl

@@ -119,10 +119,6 @@ is($psql_out, '8128', "Visible");
 # restore state
 ($node_master, $node_standby) = ($node_standby, $node_master);
 $node_standby->enable_streaming($node_master);
-$node_standby->append_conf(
-	'postgresql.conf', qq(
-recovery_target_timeline='latest'
-));
 $node_standby->start;
 $node_standby->psql(
 	'postgres',
@@ -170,10 +166,6 @@ is($psql_out, '-1', "Not visible");
 # restore state
 ($node_master, $node_standby) = ($node_standby, $node_master);
 $node_standby->enable_streaming($node_master);
-$node_standby->append_conf(
-	'postgresql.conf', qq(
-recovery_target_timeline='latest'
-));
 $node_standby->start;
 $psql_rc = $node_master->psql('postgres', "COMMIT PREPARED 'xact_012_1'");
 is($psql_rc, '0',
@@ -211,10 +203,6 @@ is($psql_out, '-1', "Not visible");
 # restore state
 ($node_master, $node_standby) = ($node_standby, $node_master);
 $node_standby->enable_streaming($node_master);
-$node_standby->append_conf(
-	'postgresql.conf', qq(
-recovery_target_timeline='latest'
-));
 $node_standby->start;
 $psql_rc = $node_master->psql('postgres', "ROLLBACK PREPARED 'xact_012_1'");
 is($psql_rc, '0',