3 files changed, 43 insertions, 16 deletions

diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c
index 82da9261566..5e0d1d067e5 100644
--- a/src/backend/storage/ipc/standby.c
+++ b/src/backend/storage/ipc/standby.c
@@ -953,14 +953,6 @@ LogAccessExclusiveLock(Oid dbOid, Oid relOid)
 {
 	xl_standby_lock xlrec;
 
-	/*
-	 * Ensure that a TransactionId has been assigned to this transaction. We
-	 * don't actually need the xid yet but if we don't do this then
-	 * RecordTransactionCommit() and RecordTransactionAbort() will optimise
-	 * away the transaction completion record which recovery relies upon to
-	 * release locks. It's a hack, but for a corner case not worth adding code
-	 * for into the main commit path.
-	 */
 	xlrec.xid = GetTopTransactionId();
 
 	/*
@@ -973,3 +965,24 @@ LogAccessExclusiveLock(Oid dbOid, Oid relOid)
 
 	LogAccessExclusiveLocks(1, &xlrec);
 }
+
+/*
+ * Prepare to log an AccessExclusiveLock, for use during LockAcquire()
+ */
+void
+LogAccessExclusiveLockPrepare(void)
+{
+	/*
+	 * Ensure that a TransactionId has been assigned to this transaction,
+	 * for two reasons, both related to lock release on the standby.
+	 * First, we must assign an xid so that RecordTransactionCommit() and
+	 * RecordTransactionAbort() do not optimise away the transaction
+	 * completion record which recovery relies upon to release locks. It's
+	 * a hack, but for a corner case not worth adding code for into the
+	 * main commit path. Second, must must assign an xid before the lock
+	 * is recorded in shared memory, otherwise a concurrently executing
+	 * GetRunningTransactionLocks() might see a lock associated with an
+	 * InvalidTransactionId which we later assert cannot happen.
+	 */
+	(void) GetTopTransactionId();
+}
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index 45cfbc07102..e7cf1cd7ad0 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -499,6 +499,7 @@ LockAcquireExtended(const LOCKTAG *locktag,
 	int			partition;
 	LWLockId	partitionLock;
 	int			status;
+	bool		log_lock = false;
 
 	if (lockmethodid <= 0 || lockmethodid >= lengthof(LockMethods))
 		elog(ERROR, "unrecognized lock method: %d", lockmethodid);
@@ -580,6 +581,24 @@ LockAcquireExtended(const LOCKTAG *locktag,
 	}
 
 	/*
+	 * Emit a WAL record if acquisition of this lock needs to be replayed in a
+	 * standby server. Only AccessExclusiveLocks can conflict with lock types
+	 * that read-only transactions can acquire in a standby server.
+	 *
+	 * Make sure this definition matches the one in GetRunningTransactionLocks().
+	 *
+	 * First we prepare to log, then after lock acquired we issue log record.
+	 */
+	if (lockmode >= AccessExclusiveLock &&
+		locktag->locktag_type == LOCKTAG_RELATION &&
+		!RecoveryInProgress() &&
+		XLogStandbyInfoActive())
+	{
+		LogAccessExclusiveLockPrepare();
+		log_lock = true;
+	}
+
+	/*
 	 * Otherwise we've got to mess with the shared lock table.
 	 */
 	hashcode = locallock->hashcode;
@@ -868,15 +887,9 @@ LockAcquireExtended(const LOCKTAG *locktag,
 
 	/*
 	 * Emit a WAL record if acquisition of this lock need to be replayed in a
-	 * standby server. Only AccessExclusiveLocks can conflict with lock types
-	 * that read-only transactions can acquire in a standby server.
-	 *
-	 * Make sure this definition matches the one GetRunningTransactionLocks().
+	 * standby server.
 	 */
-	if (lockmode >= AccessExclusiveLock &&
-		locktag->locktag_type == LOCKTAG_RELATION &&
-		!RecoveryInProgress() &&
-		XLogStandbyInfoActive())
+	if (log_lock)
 	{
 		/*
 		 * Decode the locktag back to the original values, to avoid sending
diff --git a/src/include/storage/standby.h b/src/include/storage/standby.h
index 553415c2d3a..dec1d713233 100644
--- a/src/include/storage/standby.h
+++ b/src/include/storage/standby.h
@@ -109,6 +109,7 @@ typedef struct RunningTransactionsData
 typedef RunningTransactionsData *RunningTransactions;
 
 extern void LogAccessExclusiveLock(Oid dbOid, Oid relOid);
+extern void LogAccessExclusiveLockPrepare(void);
 
 extern void LogStandbySnapshot(TransactionId *oldestActiveXid, TransactionId *nextXid);