4 files changed, 26 insertions, 1 deletions
diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c
index f8c5df08e69..59060b6080f 100644
--- a/src/backend/storage/lmgr/deadlock.c
+++ b/src/backend/storage/lmgr/deadlock.c
@@ -555,6 +555,14 @@ FindLockCycleRecurseMember(PGPROC *checkProc,
 	int			numLockModes,
 				lm;
 
+	/*
+	 * The relation extension lock can never participate in actual deadlock
+	 * cycle.  See Assert in LockAcquireExtended.  So, there is no advantage
+	 * in checking wait edges from it.
+	 */
+	if (LOCK_LOCKTAG(*lock) == LOCKTAG_RELATION_EXTEND)
+		return false;
+
 	lockMethodTable = GetLocksMethodTable(lock);
 	numLockModes = lockMethodTable->numLockModes;
 	conflictMask = lockMethodTable->conflictTab[checkProc->waitLockMode];
diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c
index be44913e2a0..5f326173429 100644
--- a/src/backend/storage/lmgr/lock.c
+++ b/src/backend/storage/lmgr/lock.c
@@ -1470,6 +1470,16 @@ LockCheckConflicts(LockMethod lockMethodTable,
 	}
 
 	/*
+	 * The relation extension lock conflict even between the group members.
+	 */
+	if (LOCK_LOCKTAG(*lock) == LOCKTAG_RELATION_EXTEND)
+	{
+		PROCLOCK_PRINT("LockCheckConflicts: conflicting (group)",
+					   proclock);
+		return true;
+	}
+
+	/*
 	 * Locks held in conflicting modes by members of our own lock group are
 	 * not real conflicts; we can subtract those out and see if we still have
 	 * a conflict.  This is O(N) in the number of processes holding or
diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index eb321f72ea4..fa07ddf4f75 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -1077,7 +1077,13 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
 
 	/*
 	 * If group locking is in use, locks held by members of my locking group
-	 * need to be included in myHeldLocks.
+	 * need to be included in myHeldLocks.  This is not required for relation
+	 * extension lock which conflict among group members. However, including
+	 * them in myHeldLocks will give group members the priority to get those
+	 * locks as compared to other backends which are also trying to acquire
+	 * those locks.  OTOH, we can avoid giving priority to group members for
+	 * that kind of locks, but there doesn't appear to be a clear advantage of
+	 * the same.
 	 */
 	if (leader != NULL)
 	{
diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h
index fc0a7128807..a89e54dbb09 100644
--- a/src/include/storage/lock.h
+++ b/src/include/storage/lock.h
@@ -301,6 +301,7 @@ typedef struct LOCK
 } LOCK;
 
 #define LOCK_LOCKMETHOD(lock) ((LOCKMETHODID) (lock).tag.locktag_lockmethodid)
+#define LOCK_LOCKTAG(lock) ((LockTagType) (lock).tag.locktag_type)
 
 
 /*