Subject: Re: could recovery_target_timeline=latest be the default in standby
 mode?
To: Michael Paquier <michael@paquier.xyz>, Sergei Kornilov <sk@zsrv.org>
References: <6dd2c23a-4162-8469-410f-bfe146e28c0c@2ndquadrant.com>
 <7495701545389660@sas1-87f9feb8d943.qloud-c.yandex.net>
 <20181221233819.GE1948@paquier.xyz>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
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Organization: 2ndQuadrant
Message-ID: <249bd41d-0385-3038-4394-a42f00e1a045@2ndquadrant.com>
Date: Thu, 27 Dec 2018 12:02:34 +0100
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On 22/12/2018 00:38, Michael Paquier wrote:
> On Fri, Dec 21, 2018 at 01:54:20PM +0300, Sergei Kornilov wrote:
>> I am +1 for recovery_target_timeline=latest by default. This is
>> common case in my opinion.
> 
> I agree also that switching to the latest timeline should be the
> default.  People get confused because of the current default.

How about this patch then?

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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From 5fd266a61c63104d8f3f4cd3e19bfc99fd22ba21 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter_e@gmx.net>
Date: Thu, 27 Dec 2018 11:49:47 +0100
Subject: [PATCH] Always use latest timeline in standby mode

In standby mode, ignore the setting of recovery_target_timeline and
always behave as if 'latest' was specified.
---
 doc/src/sgml/config.sgml                   | 15 ++++++++++++---
 doc/src/sgml/high-availability.sgml        |  8 ++------
 src/backend/access/transam/xlog.c          |  7 +++++++
 src/bin/pg_rewind/RewindTest.pm            |  2 --
 src/test/recovery/t/004_timeline_switch.pl |  1 -
 src/test/recovery/t/009_twophase.pl        | 12 ------------
 src/test/recovery/t/012_subtransactions.pl | 12 ------------
 7 files changed, 21 insertions(+), 36 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index e94b305add..76a83246ee 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -3352,13 +3352,22 @@ <title>Recovery Target</title>
        <para>
         Specifies recovering into a particular timeline.  The default is
         to recover along the same timeline that was current when the
-        base backup was taken. Setting this to <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
+        base backup was taken.  Setting this to <literal>latest</literal> recovers
+        to the latest timeline found in the archive.
+       </para>
+
+       <para>
+        You 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.
        </para>
+
+       <para>
+        In standby mode, this parameter is ignored and the latest timeline is
+        always used.  This allows a standby to follow timeline changes in
+        upstream servers.
+       </para>
       </listitem>
      </varlistentry>
 
diff --git a/doc/src/sgml/high-availability.sgml b/doc/src/sgml/high-availability.sgml
index d8fd195da0..47a93aef5b 100644
--- a/doc/src/sgml/high-availability.sgml
+++ b/doc/src/sgml/high-availability.sgml
@@ -689,10 +689,7 @@ <title>Setting Up a Standby Server</title>
     server (see <xref linkend="backup-pitr-recovery"/>). Create a file
     <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
-    that occurs at failover to another standby.
+    the WAL archive.
    </para>
 
    <note>
@@ -1023,8 +1020,7 @@ <title>Cascading Replication</title>
 
    <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>.
+    servers will continue to stream from the new master.
    </para>
 
    <para>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 5729867879..315fff48c7 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -5420,6 +5420,13 @@ validateRecoveryParameters(void)
 		!EnableHotStandby)
 		recoveryTargetAction = RECOVERY_TARGET_ACTION_SHUTDOWN;
 
+	/*
+	 * In standby mode, always use latest timeline, ignoring
+	 * recovery_target_timeline setting.
+	 */
+	if (StandbyModeRequested)
+		recoveryTargetTimeLineGoal = RECOVERY_TARGET_TIMELINE_LATEST;
+
 	/*
 	 * If user specified recovery_target_timeline, validate it or compute the
 	 * "latest" value.  We can't do this until after we've gotten the restore
diff --git a/src/bin/pg_rewind/RewindTest.pm b/src/bin/pg_rewind/RewindTest.pm
index 3d07da5d94..85cae7e47b 100644
--- a/src/bin/pg_rewind/RewindTest.pm
+++ b/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();
diff --git a/src/test/recovery/t/004_timeline_switch.pl b/src/test/recovery/t/004_timeline_switch.pl
index 79cbffb827..2b315854bc 100644
--- a/src/test/recovery/t/004_timeline_switch.pl
+++ b/src/test/recovery/t/004_timeline_switch.pl
@@ -51,7 +51,6 @@
 $node_standby_2->append_conf(
 	'postgresql.conf', qq(
 primary_conninfo='$connstr_1 application_name=@{[$node_standby_2->name]}'
-recovery_target_timeline='latest'
 ));
 $node_standby_2->restart;
 
diff --git a/src/test/recovery/t/009_twophase.pl b/src/test/recovery/t/009_twophase.pl
index dac2d4ec0d..2be1afcd8b 100644
--- a/src/test/recovery/t/009_twophase.pl
+++ b/src/test/recovery/t/009_twophase.pl
@@ -229,10 +229,6 @@ sub configure_and_reload
 
 # 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 @@ sub configure_and_reload
 
 # 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 @@ sub configure_and_reload
 
 # 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;
 
 $cur_master->psql('postgres', "COMMIT PREPARED 'xact_009_12'");
diff --git a/src/test/recovery/t/012_subtransactions.pl b/src/test/recovery/t/012_subtransactions.pl
index e26cc9c2ce..c184553694 100644
--- a/src/test/recovery/t/012_subtransactions.pl
+++ b/src/test/recovery/t/012_subtransactions.pl
@@ -119,10 +119,6 @@
 # restore state
 ($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;
 $node_standby->psql(
 	'postgres',
@@ -170,10 +166,6 @@
 # restore state
 ($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 @@
 # 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',
-- 
2.20.1


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