3 files changed, 40 insertions, 23 deletions

diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.c
index 834010ff716..8f09dc83ae7 100644
--- a/src/backend/access/transam/commit_ts.c
+++ b/src/backend/access/transam/commit_ts.c
@@ -545,19 +545,11 @@ ZeroCommitTsPage(int pageno, bool writeXlog)
 /*
  * This must be called ONCE during postmaster or standalone-backend startup,
  * after StartupXLOG has initialized ShmemVariableCache->nextXid.
- *
- * Caller may choose to enable the feature even when it is turned off in the
- * configuration.
  */
 void
-StartupCommitTs(bool enabled)
+StartupCommitTs(void)
 {
-	/*
-	 * If the module is not enabled, there's nothing to do here.  The module
-	 * could still be activated from elsewhere.
-	 */
-	if (enabled)
-		ActivateCommitTs();
+	ActivateCommitTs();
 }
 
 /*
@@ -570,9 +562,17 @@ CompleteCommitTsInitialization(void)
 	/*
 	 * If the feature is not enabled, turn it off for good.  This also removes
 	 * 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.
 	 */
 	if (!track_commit_timestamp)
 		DeactivateCommitTs();
+	else
+		ActivateCommitTs();
 }
 
 /*
@@ -591,6 +591,9 @@ CommitTsParameterChange(bool newvalue, bool oldvalue)
 	 *
 	 * If the module is disabled in the master, disable it here too, unless
 	 * the module is enabled locally.
+	 *
+	 * Note this only runs in the recovery process, so an unlocked read is
+	 * fine.
 	 */
 	if (newvalue)
 	{
@@ -620,8 +623,20 @@ CommitTsParameterChange(bool newvalue, bool oldvalue)
 static void
 ActivateCommitTs(void)
 {
-	TransactionId xid = ShmemVariableCache->nextXid;
-	int			pageno = TransactionIdToCTsPage(xid);
+	TransactionId xid;
+	int			pageno;
+
+	/* If we've done this already, there's nothing to do */
+	LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
+	if (commitTsShared->commitTsActive)
+	{
+		LWLockRelease(CommitTsLock);
+		return;
+	}
+	LWLockRelease(CommitTsLock);
+
+	xid = ShmemVariableCache->nextXid;
+	pageno = TransactionIdToCTsPage(xid);
 
 	/*
 	 * Re-Initialize our idea of the latest page number.
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 86debf44123..71fc8ffa272 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -6339,6 +6339,14 @@ 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.
+	 */
+	if (ArchiveRecoveryRequested ?
+		ControlFile->track_commit_timestamp : track_commit_timestamp)
+		StartupCommitTs();
+
+	/*
 	 * Recover knowledge about replay progress of known replication partners.
 	 */
 	StartupReplicationOrigin();
@@ -6565,16 +6573,11 @@ StartupXLOG(void)
 			ProcArrayInitRecovery(ShmemVariableCache->nextXid);
 
 			/*
-			 * Startup commit log, commit timestamp and subtrans only.
-			 * MultiXact has already been started up and other SLRUs are not
+			 * Startup commit log and subtrans only.  MultiXact and commit
+			 * timestamp have already been started up and other SLRUs are not
 			 * maintained during recovery and need not be started yet.
-			 *
-			 * For commit timestamps, we do this based on the control file
-			 * info: in a standby, we want to drive it off the state of the
-			 * master, not local configuration.
 			 */
 			StartupCLOG();
-			StartupCommitTs(ControlFile->track_commit_timestamp);
 			StartupSUBTRANS(oldestActiveXID);
 
 			/*
@@ -7337,13 +7340,12 @@ StartupXLOG(void)
 	LWLockRelease(ProcArrayLock);
 
 	/*
-	 * Start up the commit log, commit timestamp and subtrans, if not already
-	 * done for hot standby.
+	 * Start up the commit log and subtrans, if not already done for hot
+	 * standby.  (commit timestamps are started below, if necessary.)
 	 */
 	if (standbyState == STANDBY_DISABLED)
 	{
 		StartupCLOG();
-		StartupCommitTs(track_commit_timestamp);
 		StartupSUBTRANS(oldestActiveXID);
 	}
 
diff --git a/src/include/access/commit_ts.h b/src/include/access/commit_ts.h
index f5b39691e71..425f25870fd 100644
--- a/src/include/access/commit_ts.h
+++ b/src/include/access/commit_ts.h
@@ -34,7 +34,7 @@ extern Size CommitTsShmemBuffers(void);
 extern Size CommitTsShmemSize(void);
 extern void CommitTsShmemInit(void);
 extern void BootStrapCommitTs(void);
-extern void StartupCommitTs(bool enabled);
+extern void StartupCommitTs(void);
 extern void CommitTsParameterChange(bool xlrecvalue, bool pgcontrolvalue);
 extern void CompleteCommitTsInitialization(void);
 extern void ShutdownCommitTs(void);