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Commit8d28bf5

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Rework activation of commit timestamps during recovery
The activation and deactivation of commit timestamp tracking has notbeen handled consistently for a primary or standbys at recovery. Thefacility can be activated at three different moments of recovery:- The beginning, where a primary would use the GUC value for thedecision-making, and where a standby relies on the contents of thecontrol file.- When replaying a XLOG_PARAMETER_CHANGE record at redo.- The end, where both primary and standby rely on the GUC value.Using the GUC value for a primary at the beginning of recovery causesproblems with commit timestamp access when doing crash recovery.Particularly, when replaying transaction commits, it could be possiblethat an attempt to read commit timestamps is done for a transactionwhich committed at a moment when track_commit_timestamp was disabled.A test case is added to reproduce the failure. The test works down tov11 as it takes advantage of transaction commits within procedures.Reported-by: Hailong LiAuthor: Masahiko Sawasa, Michael PaquierReviewed-by: Kyotaro HoriguchiDiscussion:https://postgr.es/m/11224478-a782-203b-1f17-e4797b39bdf0@qunar.comBackpatch-through: 9.5, where commit timestamps have been introduced.
1 parent1076335 commit8d28bf5

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3 files changed

+40
-14
lines changed

3 files changed

+40
-14
lines changed

‎src/backend/access/transam/commit_ts.c

Lines changed: 4 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -573,10 +573,9 @@ CompleteCommitTsInitialization(void)
573573
* any leftover data.
574574
*
575575
* Conversely, we activate the module if the feature is enabled. This is
576-
* not necessary in a master system because we already did it earlier, but
577-
* if we're in a standby server that got promoted which had the feature
578-
* enabled and was following a master that had the feature disabled, this
579-
* is where we turn it on locally.
576+
* necessary for primary and standby as the activation depends on the
577+
* control file contents at the beginning of recovery or when a
578+
* XLOG_PARAMETER_CHANGE is replayed.
580579
*/
581580
if (!track_commit_timestamp)
582581
DeactivateCommitTs();
@@ -586,7 +585,7 @@ CompleteCommitTsInitialization(void)
586585

587586
/*
588587
* Activate or deactivate CommitTs' upon reception of a XLOG_PARAMETER_CHANGE
589-
* XLog recordin a standby.
588+
* XLog recordduring recovery.
590589
*/
591590
void
592591
CommitTsParameterChange(boolnewvalue,boololdvalue)

‎src/backend/access/transam/xlog.c

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -6833,11 +6833,12 @@ StartupXLOG(void)
68336833
StartupMultiXact();
68346834

68356835
/*
6836-
* Ditto commit timestamps. In a standby, we do it if setting is enabled
6837-
* in ControlFile; in a master we base the decision on the GUC itself.
6836+
* Ditto for commit timestamps. Activate the facility if the setting is
6837+
* enabled in the control file, as there should be no tracking of commit
6838+
* timestamps done when the setting was disabled. This facility can be
6839+
* started or stopped when replaying a XLOG_PARAMETER_CHANGE record.
68386840
*/
6839-
if (ArchiveRecoveryRequested ?
6840-
ControlFile->track_commit_timestamp :track_commit_timestamp)
6841+
if (ControlFile->track_commit_timestamp)
68416842
StartupCommitTs();
68426843

68436844
/*

‎src/test/modules/commit_ts/t/004_restart.pl

Lines changed: 31 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
# Testing of commit timestamps preservation acrosscleanrestarts
1+
# Testing of commit timestamps preservation across restarts
22
use strict;
33
use warnings;
44
use PostgresNode;
@@ -71,12 +71,36 @@
7171
'timestamps before and after restart are equal');
7272

7373
# Now disable commit timestamps
74-
7574
$node_master->append_conf('postgresql.conf','track_commit_timestamp = off');
76-
7775
$node_master->stop('fast');
76+
77+
# Start the server, which generates a XLOG_PARAMETER_CHANGE record where
78+
# the parameter change is registered.
7879
$node_master->start;
7980

81+
# Now restart again the server so as no XLOG_PARAMETER_CHANGE record are
82+
# replayed with the follow-up immediate shutdown.
83+
$node_master->restart;
84+
85+
# Move commit timestamps across page boundaries. Things should still
86+
# be able to work across restarts with those transactions committed while
87+
# track_commit_timestamp is disabled.
88+
$node_master->safe_psql('postgres',
89+
qq(CREATE PROCEDURE consume_xid(cnt int)
90+
AS\$\$
91+
DECLARE
92+
i int;
93+
BEGIN
94+
FOR i in 1..cnt LOOP
95+
EXECUTE 'SELECT txid_current()';
96+
COMMIT;
97+
END LOOP;
98+
END;
99+
\$\$
100+
LANGUAGE plpgsql;
101+
));
102+
$node_master->safe_psql('postgres','CALL consume_xid(2000)');
103+
80104
($ret,$stdout,$stderr) =$node_master->psql('postgres',
81105
qq[SELECT pg_xact_commit_timestamp('$xid');]);
82106
is($ret, 3,'no commit timestamp from enable tx when cts disabled');
@@ -106,10 +130,12 @@
106130
# Re-enable, restart and ensure we can still get the old timestamps
107131
$node_master->append_conf('postgresql.conf','track_commit_timestamp = on');
108132

109-
$node_master->stop('fast');
133+
# An immediate shutdown is used here. At next startup recovery will
134+
# replay transactions which committed when track_commit_timestamp was
135+
# disabled, and the facility should be able to work properly.
136+
$node_master->stop('immediate');
110137
$node_master->start;
111138

112-
113139
my$after_enable_ts =$node_master->safe_psql('postgres',
114140
qq[SELECT pg_xact_commit_timestamp('$xid');]);
115141
is($after_enable_ts,'','timestamp of enabled tx null after re-enable');

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