postgrespro
diff --git a/‎src/backend/postmaster/autovacuum.c
Lines changed: 20 additions & 1 deletion b/‎src/backend/postmaster/autovacuum.c
Lines changed: 20 additions & 1 deletion
diff --git a/‎src/backend/storage/lmgr/lmgr.c
Lines changed: 38 additions & 0 deletions b/‎src/backend/storage/lmgr/lmgr.c
Lines changed: 38 additions & 0 deletions
diff --git a/‎src/include/storage/lmgr.h
Lines changed: 2 additions & 0 deletions b/‎src/include/storage/lmgr.h
Lines changed: 2 additions & 0 deletions
@@ -76,6 +76,7 @@
 #include "catalog/dependency.h"
 #include "catalog/namespace.h"
 #include "catalog/pg_database.h"
+#include "catalog/pg_namespace.h"
 #include "commands/dbcommands.h"
 #include "commands/vacuum.h"
 #include "common/int.h"
@@ -2175,6 +2176,24 @@ do_autovacuum(void)
 			continue;
 		}
 
+		/*
+		 * Try to lock the temp namespace, too.  Even though we have lock on
+		 * the table itself, there's a risk of deadlock against an incoming
+		 * backend trying to clean out the temp namespace, in case this table
+		 * has dependencies (such as sequences) that the backend's
+		 * performDeletion call might visit in a different order.  If we can
+		 * get AccessShareLock on the namespace, that's sufficient to ensure
+		 * we're not running concurrently with RemoveTempRelations.  If we
+		 * can't, back off and let RemoveTempRelations do its thing.
+		 */
+		if (!ConditionalLockDatabaseObject(NamespaceRelationId,
+										   classForm->relnamespace, 0,
+										   AccessShareLock))
+		{
+			UnlockRelationOid(relid, AccessExclusiveLock);
+			continue;
+		}
+
 		/* OK, let's delete it */
 		ereport(LOG,
 				(errmsg("autovacuum: dropping orphan temp table \"%s.%s.%s\"",
@@ -2192,7 +2211,7 @@ do_autovacuum(void)
 
 		/*
 		 * To commit the deletion, end current transaction and start a new
-		 * one.  Note this also releases the lock we took.
+		 * one.  Note this also releases the locks we took.
 		 */
 		CommitTransactionCommand();
 		StartTransactionCommand();
 
@@ -1018,6 +1018,44 @@ LockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
 	AcceptInvalidationMessages();
 }
 
+/*
+ *		ConditionalLockDatabaseObject
+ *
+ * As above, but only lock if we can get the lock without blocking.
+ * Returns true iff the lock was acquired.
+ */
+bool
+ConditionalLockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
+							  LOCKMODE lockmode)
+{
+	LOCKTAG		tag;
+	LOCALLOCK  *locallock;
+	LockAcquireResult res;
+
+	SET_LOCKTAG_OBJECT(tag,
+					   MyDatabaseId,
+					   classid,
+					   objid,
+					   objsubid);
+
+	res = LockAcquireExtended(&tag, lockmode, false, true, true, &locallock);
+
+	if (res == LOCKACQUIRE_NOT_AVAIL)
+		return false;
+
+	/*
+	 * Now that we have the lock, check for invalidation messages; see notes
+	 * in LockRelationOid.
+	 */
+	if (res != LOCKACQUIRE_ALREADY_CLEAR)
+	{
+		AcceptInvalidationMessages();
+		MarkLockClear(locallock);
+	}
+
+	return true;
+}
+
 /*
  *		UnlockDatabaseObject
  */
 
@@ -93,6 +93,8 @@ extern void SpeculativeInsertionWait(TransactionId xid, uint32 token);
 /* Lock a general object (other than a relation) of the current database */
 extern void LockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
 							   LOCKMODE lockmode);
+extern bool ConditionalLockDatabaseObject(Oid classid, Oid objid,
+										  uint16 objsubid, LOCKMODE lockmode);
 extern void UnlockDatabaseObject(Oid classid, Oid objid, uint16 objsubid,
 								 LOCKMODE lockmode);