Subquery pushdown planner uses original query

With this commit, we change the input to the logical planner for
subquery pushdown. Before this commit, the planner was relying
on the query tree that is transformed by the postgresql planner.
After this commit, the planner uses the original query. The main
motivation behind this change is the simplify deparsing of
subqueries.

src/backend/distributed/planner/multi_logical_planner.c

@@ -104,28 +104,35 @@ static MultiNode * ApplyCartesianProduct(MultiNode *leftNode, MultiNode *rightNo
  * Local functions forward declarations for subquery pushdown. Note that these
  * functions will be removed with upcoming subqery changes.
  */
-static MultiNode * SubqueryPushdownMultiPlanTree(Query *queryTree,
+static MultiNode * SubqueryPushdownMultiPlanTree(Query *queryTree);
-												 List *subqueryEntryList);
 static void ErrorIfSubqueryJoin(Query *queryTree);
 static MultiTable * MultiSubqueryPushdownTable(RangeTblEntry *subqueryRangeTableEntry);
 
 
 /*
- * MultiLogicalPlanCreate takes in a parsed query tree, uses helper functions to
+ * MultiLogicalPlanCreate takes in both the original query and its corresponding modified
- * create logical plan and adds a root node to top of it.
+ * query tree yield by the standard planner. It uses helper functions to create logical
+ * plan and adds a root node to top of it. The  original query is only used for subquery
+ * pushdown planning.
  */
 MultiTreeRoot *
-MultiLogicalPlanCreate(Query *queryTree)
+MultiLogicalPlanCreate(Query *originalQuery, Query *queryTree)
 {
 	MultiNode *multiQueryNode = NULL;
 	MultiTreeRoot *rootNode = NULL;
+	List *subqueryEntryList = NULL;
 
-	List *subqueryEntryList = SubqueryEntryList(queryTree);
+	/*
+	 * We check the existence of subqueries in the modified query given that
+	 * if postgres already flattened the subqueries, MultiPlanTree() can plan
+	 * corresponding distributed plan.
+	 */
+	subqueryEntryList = SubqueryEntryList(queryTree);
 	if (subqueryEntryList != NIL)
 	{
 		if (SubqueryPushdown)
 		{
-			multiQueryNode = SubqueryPushdownMultiPlanTree(queryTree, subqueryEntryList);
+			multiQueryNode = SubqueryPushdownMultiPlanTree(originalQuery);
 		}
 		else
 		{
@@ -1982,7 +1989,7 @@ ApplyCartesianProduct(MultiNode *leftNode, MultiNode *rightNode,
  * from other parts of code although it causes some code duplication.
  */
 static MultiNode *
-SubqueryPushdownMultiPlanTree(Query *queryTree, List *subqueryEntryList)
+SubqueryPushdownMultiPlanTree(Query *queryTree)
 {
 	List *targetEntryList = queryTree->targetList;
 	List *qualifierList = NIL;
@@ -1997,6 +2004,7 @@ SubqueryPushdownMultiPlanTree(Query *queryTree, List *subqueryEntryList)
 	MultiExtendedOp *extendedOpNode = NULL;
 	MultiNode *currentTopNode = NULL;
 	RangeTblEntry *subqueryRangeTableEntry = NULL;
+	List *subqueryEntryList = SubqueryEntryList(queryTree);
 
 	/* verify we can perform distributed planning on this query */
 	ErrorIfQueryNotSupported(queryTree);

src/backend/distributed/planner/multi_planner.c

@@ -311,7 +311,7 @@ CreateDistributedPlan(PlannedStmt *localPlan, Query *originalQuery, Query *query
 		if ((!distributedPlan || distributedPlan->planningError) && !hasUnresolvedParams)
 		{
 			/* Create and optimize logical plan */
-			MultiTreeRoot *logicalPlan = MultiLogicalPlanCreate(query);
+			MultiTreeRoot *logicalPlan = MultiLogicalPlanCreate(originalQuery, query);
 			MultiLogicalPlanOptimize(logicalPlan, plannerRestrictionContext);
 
 			/*

src/include/distributed/multi_logical_planner.h

@@ -180,7 +180,7 @@ extern bool SubqueryPushdown;
 
 
 /* Function declarations for building logical plans */
-extern MultiTreeRoot * MultiLogicalPlanCreate(Query *queryTree);
+extern MultiTreeRoot * MultiLogicalPlanCreate(Query *originalQuery, Query *queryTree);
 extern bool NeedsDistributedPlanning(Query *queryTree);
 extern MultiNode * ParentNode(MultiNode *multiNode);
 extern MultiNode * ChildNode(MultiUnaryNode *multiNode);

src/test/regress/output/multi_subquery.source

@@ -178,7 +178,8 @@ SELECT count(*) FROM
    (SELECT l_orderkey FROM lineitem_subquery) UNION ALL
    (SELECT 1::bigint)
 ) b;
-ERROR:  could not run distributed query with complex table expressions
+ERROR:  cannot push down this subquery
+DETAIL:  Union All clauses are currently unsupported
 ---
 -- TEMPORARLY DISABLE UNIONS WITHOUT JOINS
 ---

src/test/regress/output/multi_subquery_0.source

@@ -178,7 +178,8 @@ SELECT count(*) FROM
    (SELECT l_orderkey FROM lineitem_subquery) UNION ALL
    (SELECT 1::bigint)
 ) b;
-ERROR:  could not run distributed query with complex table expressions
+ERROR:  cannot push down this subquery
+DETAIL:  Union All clauses are currently unsupported
 ---
 -- TEMPORARLY DISABLE UNIONS WITHOUT JOINS
 ---