temp commit for multi task router

src/backend/distributed/executor/multi_server_executor.c

@@ -127,18 +127,32 @@ RouterExecutablePlan(MultiPlan *multiPlan, MultiExecutorType executorType)
 	List *workerDependentTaskList = NIL;
 	bool masterQueryHasAggregates = false;
 
-	/* TODO: this is a hacky solution to allow 0 shard INSERT ... SELECT */
+	if (executorType == MULTI_EXECUTOR_TASK_TRACKER)
-	if (masterQuery == NULL)
-	{
-		return true;
-	}
-
-	/* router executor cannot execute queries that hit zero shards */
-	if (taskCount == 0)
 	{
 		return false;
 	}
 
+	/* router executor cannot execute repartition jobs */
+	if (dependedJobCount > 0)
+	{
+		return false;
+	}
+
+	/* router executor cannot execute plans when master query is present */
+	if (masterQuery != NULL)
+	{
+		return false;
+	}
+
+	/*
+	 * Multi task router executor can execute plans with zero task. This is currently
+	 * here for INSERT ... SELECT queries with zero shards.
+	 */
+	if (taskCount == 0)
+	{
+		return true;
+	}
+
 	/* check if the first task is a modify or a router task, short-circuit if so */
 	workerTask = (Task *) linitial(workerTaskList);
 	taskType = workerTask->taskType;
@@ -148,18 +162,7 @@ RouterExecutablePlan(MultiPlan *multiPlan, MultiExecutorType executorType)
 	}
 
 	/* router executor cannot execute SELECT queries that hit more than one shard */
-	if (taskCount != 1)
+	if (taskCount != 1 && taskType == ROUTER_TASK)
-	{
-		return false;
-	}
-
-	if (executorType == MULTI_EXECUTOR_TASK_TRACKER)
-	{
-		return false;
-	}
-
-	/* router executor cannot execute repartition jobs */
-	if (dependedJobCount > 0)
 	{
 		return false;
 	}

src/test/regress/sql/multi_insert_select.sql

@@ -101,6 +101,14 @@ FROM
 WHERE
    0 != 0;
 
+INSERT INTO raw_events_second (value_2, value_1, value_3, value_4, user_id, time)
+SELECT
+   value_2, value_1, value_3, value_4, user_id, time
+FROM
+   raw_events_first
+WHERE
+   user_id = 15 AND user_id = 16;
+
 -- add one more row
 SET client_min_messages TO INFO;
 INSERT INTO raw_events_first (user_id, time, value_1, value_2, value_3, value_4) VALUES