[PGPRO-6538] Changed lock order

The parent table is locked first and then are locked the partitions.

Author: kovdb75

src/pl_range_funcs.c

@@ -683,9 +683,6 @@ merge_range_partitions(PG_FUNCTION_ARGS)
 		/* Extract partition Oids from array */
 		parts[i] = DatumGetObjectId(datums[i]);
 
-		/* Prevent modification of partitions */
-		LockRelationOid(parts[i], AccessExclusiveLock);
-
 		/* Check if all partitions are from the same parent */
 		cur_parent = get_parent_of_partition(parts[i]);
 
@@ -708,6 +705,10 @@ merge_range_partitions(PG_FUNCTION_ARGS)
 	/* Prevent changes in partitioning scheme */
 	LockRelationOid(parent, ShareUpdateExclusiveLock);
 
+	/* Prevent modification of partitions */
+	for (i = 0; i < nparts; i++)
+		LockRelationOid(parts[i], AccessExclusiveLock);
+
 	/* Emit an error if it is not partitioned by RANGE */
 	prel = get_pathman_relation_info(parent);
 	shout_if_prel_is_invalid(parent, prel, PT_RANGE);