Rework activation of commit timestamps during recovery

michaelpq · michaelpq · commit e513a3d854a1 · 2018-09-26T10:29:49.000+09:00
The activation and deactivation of commit timestamp tracking has not been handled consistently for a primary or standbys at recovery. The facility can be activated at three different moments of recovery: - The beginning, where a primary would use the GUC value for the decision-making, and where a standby relies on the contents of the control 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 causes problems with commit timestamp access when doing crash recovery. Particularly, when replaying transaction commits, it could be possible that an attempt to read commit timestamps is done for a transaction which committed at a moment when track_commit_timestamp was disabled. A test case is added to reproduce the failure. The test works down to v11 as it takes advantage of transaction commits within procedures. Reported-by: Hailong Li Author: Masahiko Sawasa, Michael Paquier Reviewed-by: Kyotaro Horiguchi Discussion: https://postgr.es/m/11224478-a782-203b-1f17-e4797b39bdf0@qunar.com Backpatch-through: 9.5, where commit timestamps have been introduced.
diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.c
@@ -572,10 +572,9 @@ CompleteCommitTsInitialization(void)
 	 * any leftover data.
 	 *
 	 * Conversely, we activate the module if the feature is enabled.  This is
-	 * not necessary in a master system because we already did it earlier, but
-	 * if we're in a standby server that got promoted which had the feature
-	 * enabled and was following a master that had the feature disabled, this
-	 * is where we turn it on locally.
+	 * necessary for primary and standby as the activation depends on the
+	 * control file contents at the beginning of recovery or when a
+	 * XLOG_PARAMETER_CHANGE is replayed.
 	 */
 	if (!track_commit_timestamp)
 		DeactivateCommitTs();
@@ -585,7 +584,7 @@ CompleteCommitTsInitialization(void)
 
 /*
  * Activate or deactivate CommitTs' upon reception of a XLOG_PARAMETER_CHANGE
- * XLog record in a standby.
+ * XLog record during recovery.
  */
 void
 CommitTsParameterChange(bool newvalue, bool oldvalue)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -6467,11 +6467,12 @@ StartupXLOG(void)
 	StartupMultiXact();
 
 	/*
-	 * Ditto commit timestamps.  In a standby, we do it if setting is enabled
-	 * in ControlFile; in a master we base the decision on the GUC itself.
+	 * Ditto for commit timestamps.  Activate the facility if the setting is
+	 * enabled in the control file, as there should be no tracking of commit
+	 * timestamps done when the setting was disabled.  This facility can be
+	 * started or stopped when replaying a XLOG_PARAMETER_CHANGE record.
 	 */
-	if (ArchiveRecoveryRequested ?
-		ControlFile->track_commit_timestamp : track_commit_timestamp)
+	if (ControlFile->track_commit_timestamp)
 		StartupCommitTs();
 
 	/*
