From 32b7e152a3518e199d965a2744cc7cd787bb3a3e Mon Sep 17 00:00:00 2001
From: metdos <metin@citusdata.com>
Date: Thu, 21 Dec 2017 12:53:48 +0200
Subject: [PATCH] Get shard resource locks for only DMLs

---
 .../distributed/executor/multi_router_executor.c      | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/src/backend/distributed/executor/multi_router_executor.c b/src/backend/distributed/executor/multi_router_executor.c
index 6ac238d88..04b4beb15 100644
--- a/src/backend/distributed/executor/multi_router_executor.c
+++ b/src/backend/distributed/executor/multi_router_executor.c
@@ -1063,8 +1063,15 @@ ExecuteModifyTasks(List *taskList, bool expectResults, ParamListInfo paramListIn
 		LockPartitionRelations(firstShardInterval->relationId, RowExclusiveLock);
 	}
 
-	/* ensure that there are no concurrent modifications on the same shards */
-	AcquireExecutorMultiShardLocks(taskList);
+	/*
+	 * Ensure that there are no concurrent modifications on the same
+	 * shards. For DDL commands, we already obtained the appropriate
+	 * locks in ProcessUtility.
+	 */
+	if (firstTask->taskType == MODIFY_TASK)
+	{
+		AcquireExecutorMultiShardLocks(taskList);
+	}
 
 	BeginOrContinueCoordinatedTransaction();