Merge pull request #3722 from citusdata/optimistic-duplicate-grouping

Duplicate grouping on worker whenever possible

src/backend/distributed/planner/multi_logical_optimizer.c

@@ -328,9 +328,6 @@ static bool HasOrderByAggregate(List *sortClauseList, List *targetList);
 static bool HasOrderByNonCommutativeAggregate(List *sortClauseList, List *targetList);
 static bool HasOrderByComplexExpression(List *sortClauseList, List *targetList);
 static bool HasOrderByHllType(List *sortClauseList, List *targetList);
-static bool ShouldPushDownGroupingToWorker(MultiExtendedOp *opNode,
-										   ExtendedOpNodeProperties *
-										   extendedOpNodeProperties);
 static bool ShouldProcessDistinctOrderAndLimitForWorker(
 	ExtendedOpNodeProperties *extendedOpNodeProperties,
 	bool pushingDownOriginalGrouping,
@@ -2223,7 +2220,7 @@ WorkerExtendedOpNode(MultiExtendedOp *originalOpNode,
 	/* targetProjectionNumber starts from 1 */
 	queryTargetList.targetProjectionNumber = 1;
 
-	if (ShouldPushDownGroupingToWorker(originalOpNode, extendedOpNodeProperties))
+	if (!extendedOpNodeProperties->pullUpIntermediateRows)
 	{
 		queryGroupClause.groupClauseList = copyObject(originalGroupClauseList);
 	}
@@ -4717,46 +4714,6 @@ HasOrderByHllType(List *sortClauseList, List *targetList)
 }
 
 
-/*
- * ShouldPushDownGroupingToWorker returns whether we push down GROUP BY.
- * This may return true even when GROUP BY is necessary on master.
- */
-static bool
-ShouldPushDownGroupingToWorker(MultiExtendedOp *opNode,
-							   ExtendedOpNodeProperties *extendedOpNodeProperties)
-{
-	if (extendedOpNodeProperties->pushDownGroupingAndHaving)
-	{
-		return true;
-	}
-
-	if (extendedOpNodeProperties->pullUpIntermediateRows)
-	{
-		return false;
-	}
-
-	/*
-	 * Duplicate grouping if we have LIMIT without HAVING, as this can
-	 * often result in LIMIT being pushed down.
-	 */
-	if (opNode->havingQual == NULL && opNode->limitCount != NULL)
-	{
-		return true;
-	}
-
-	/*
-	 * If aggregates are being split across worker & master, so must grouping.
-	 */
-	if (contain_aggs_of_level(opNode->havingQual, 0) ||
-		contain_aggs_of_level((Node *) opNode->targetList, 0))
-	{
-		return true;
-	}
-
-	return false;
-}
-
-
 /*
  * ShouldProcessDistinctOrderAndLimitForWorker returns whether
  * ProcessDistinctClauseForWorkerQuery should be called. If not,

src/test/regress/expected/multi_explain.out

@@ -453,8 +453,11 @@ HashAggregate
         Tasks Shown: One of 2
         ->  Task
               Node: host=localhost port=xxxxx dbname=regression
-              ->  Seq Scan on public.lineitem_290000 lineitem
+              ->  HashAggregate
                     Output: l_quantity, l_quantity
+                    Group Key: lineitem.l_quantity
+                    ->  Seq Scan on public.lineitem_290000 lineitem
+                          Output: l_orderkey, l_partkey, l_suppkey, l_linenumber, l_quantity, l_extendedprice, l_discount, l_tax, l_returnflag, l_linestatus, l_shipdate, l_commitdate, l_receiptdate, l_shipinstruct, l_shipmode, l_comment
 -- Subquery pushdown tests with explain
 EXPLAIN (COSTS OFF)
 SELECT

src/test/regress/expected/multi_view.out

@@ -747,7 +747,7 @@ RESET citus.subquery_pushdown;
 VACUUM ANALYZE users_table;
 -- explain tests
 EXPLAIN (COSTS FALSE) SELECT user_id FROM recent_selected_users GROUP BY 1 ORDER BY 1;
-                                                              QUERY PLAN
+                                                                 QUERY PLAN
 ---------------------------------------------------------------------
  Sort
    Sort Key: remote_scan.user_id
@@ -758,17 +758,19 @@ EXPLAIN (COSTS FALSE) SELECT user_id FROM recent_selected_users GROUP BY 1 ORDER
                Tasks Shown: One of 4
                ->  Task
                      Node: host=localhost port=xxxxx dbname=regression
-                     ->  Nested Loop
+                     ->  HashAggregate
-                           Join Filter: (users_table.user_id = users_table_1.user_id)
+                           Group Key: users_table.user_id
-                           ->  Sort
+                           ->  Nested Loop
-                                 Sort Key: (max(users_table_1."time")) DESC
+                                 Join Filter: (users_table.user_id = users_table_1.user_id)
-                                 ->  HashAggregate
+                                 ->  Sort
-                                       Group Key: users_table_1.user_id
+                                       Sort Key: (max(users_table_1."time")) DESC
-                                       Filter: (max(users_table_1."time") > '2017-11-23 16:20:33.264457'::timestamp without time zone)
+                                       ->  HashAggregate
-                                       ->  Seq Scan on users_table_1400256 users_table_1
+                                             Group Key: users_table_1.user_id
-                           ->  Seq Scan on users_table_1400256 users_table
+                                             Filter: (max(users_table_1."time") > '2017-11-23 16:20:33.264457'::timestamp without time zone)
-                                 Filter: ((value_1 >= 1) AND (value_1 < 3))
+                                             ->  Seq Scan on users_table_1400256 users_table_1
-(19 rows)
+                                 ->  Seq Scan on users_table_1400256 users_table
+                                       Filter: ((value_1 >= 1) AND (value_1 < 3))
+(21 rows)
 
 EXPLAIN (COSTS FALSE) SELECT *
 	FROM (