Merge pull request #4253 from citusdata/improve_perf_for_queries

Improve the relation restriction counters

src/backend/distributed/planner/relation_restriction_equivalence.c

@@ -534,9 +534,8 @@ ContainsMultipleDistributedRelations(PlannerRestrictionContext *
 	RelationRestrictionContext *restrictionContext =
 		plannerRestrictionContext->relationRestrictionContext;
 
-	uint32 referenceRelationCount = ReferenceRelationCount(restrictionContext);
-	uint32 totalRelationCount = list_length(restrictionContext->relationRestrictionList);
-	uint32 nonReferenceRelationCount = totalRelationCount - referenceRelationCount;
+	uint32 distributedRelationCount =
+		UniqueRelationCount(restrictionContext, DISTRIBUTED_TABLE);
 
 	/*
 	 * If the query includes a single relation which is not a reference table,
@@ -551,7 +550,7 @@ ContainsMultipleDistributedRelations(PlannerRestrictionContext *
 	 * tasks that are going to be created should not need data from other tasks. In both
 	 * cases mentioned above, the necessary data per task would be on available.
 	 */
-	if (nonReferenceRelationCount <= 1)
+	if (distributedRelationCount <= 1)
 	{
 		return false;
 	}
@@ -591,29 +590,39 @@ GenerateAllAttributeEquivalences(PlannerRestrictionContext *plannerRestrictionCo
 
 
 /*
- * ReferenceRelationCount iterates over the relations and returns the reference table
- * relation count.
+ * UniqueRelationCount iterates over the relations and returns the
+ * unique relation count. We use RTEIdentity as the identifiers, so if
+ * the same relation appears twice in the restrictionContext, we count
+ * it as a single item.
  */
 uint32
-ReferenceRelationCount(RelationRestrictionContext *restrictionContext)
+UniqueRelationCount(RelationRestrictionContext *restrictionContext, CitusTableType
+					tableType)
 {
 	ListCell *relationRestrictionCell = NULL;
-	uint32 referenceRelationCount = 0;
+	List *rteIdentityList = NIL;
 
 	foreach(relationRestrictionCell, restrictionContext->relationRestrictionList)
 	{
 		RelationRestriction *relationRestriction =
 			(RelationRestriction *) lfirst(relationRestrictionCell);
-		CitusTableCacheEntry *cacheEntry = GetCitusTableCacheEntry(
-			relationRestriction->relationId);
+		Oid relationId = relationRestriction->relationId;
 
-		if (IsCitusTableTypeCacheEntry(cacheEntry, REFERENCE_TABLE))
+		CitusTableCacheEntry *cacheEntry = LookupCitusTableCacheEntry(relationId);
+		if (cacheEntry == NULL)
 		{
-			referenceRelationCount++;
+			/* we  don't expect non-distributed tables, still be no harm to skip */
+			continue;
+		}
+
+		if (IsCitusTableTypeCacheEntry(cacheEntry, tableType))
+		{
+			int rteIdentity = GetRTEIdentity(relationRestriction->rte);
+			rteIdentityList = list_append_unique_int(rteIdentityList, rteIdentity);
 		}
 	}
 
-	return referenceRelationCount;
+	return list_length(rteIdentityList);
 }
 
 
@@ -1805,10 +1814,10 @@ FilterPlannerRestrictionForQuery(PlannerRestrictionContext *plannerRestrictionCo
 	filteredPlannerRestrictionContext->memoryContext =
 		plannerRestrictionContext->memoryContext;
 
-	int totalRelationCount = list_length(
-		filteredRelationRestrictionContext->relationRestrictionList);
-	int referenceRelationCount = ReferenceRelationCount(
-		filteredRelationRestrictionContext);
+	int totalRelationCount = UniqueRelationCount(
+		filteredRelationRestrictionContext, ANY_CITUS_TABLE_TYPE);
+	int referenceRelationCount = UniqueRelationCount(
+		filteredRelationRestrictionContext, REFERENCE_TABLE);
 
 	filteredRelationRestrictionContext->allReferenceTables =
 		(totalRelationCount == referenceRelationCount);

src/include/distributed/relation_restriction_equivalence.h

@@ -13,7 +13,7 @@
 #define RELATION_RESTRICTION_EQUIVALENCE_H
 
 #include "distributed/distributed_planner.h"
-
+#include "distributed/metadata_cache.h"
 
 extern bool AllDistributionKeysInQueryAreEqual(Query *originalQuery,
 											   PlannerRestrictionContext *
@@ -29,7 +29,8 @@ bool RestrictionEquivalenceForPartitionKeysViaEquivalences(PlannerRestrictionCon
 														   allAttributeEquivalenceList);
 extern List * GenerateAllAttributeEquivalences(PlannerRestrictionContext *
 											   plannerRestrictionContext);
-extern uint32 ReferenceRelationCount(RelationRestrictionContext *restrictionContext);
+extern uint32 UniqueRelationCount(RelationRestrictionContext *restrictionContext,
+								  CitusTableType tableType);
 
 extern List * DistributedRelationIdList(Query *query);
 extern PlannerRestrictionContext * FilterPlannerRestrictionForQuery(

src/test/regress/expected/subquery_basics.out

@@ -2,6 +2,65 @@
 -- test recursive planning functionality
 -- ===================================================================
 SET client_min_messages TO DEBUG1;
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	user_id, value_1
+FROM
+	(SELECT user_id, value_1 FROM users_table) as foo
+ORDER BY 1 DESC, 2 DESC LIMIT 3;
+DEBUG:  push down of limit count: 3
+ user_id | value_1
+---------------------------------------------------------------------
+       6 |       5
+       6 |       5
+       6 |       3
+(3 rows)
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	sum(sel_val_1), sum(sel_val_2)
+FROM
+	(SELECT max(value_1) as  sel_val_1, min(value_2) as sel_val_2 FROM users_table GROUP BY user_id) as foo;
+ sum | sum
+---------------------------------------------------------------------
+  29 |   1
+(1 row)
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	min(user_id), max(value_1)
+FROM
+	(SELECT user_id, value_1 FROM users_table) as foo;
+ min | max
+---------------------------------------------------------------------
+   1 |   5
+(1 row)
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	min(user_id)
+FROM
+	(SELECT user_id, value_1 FROM users_table GROUP BY user_id, value_1) as bar;
+ min
+---------------------------------------------------------------------
+   1
+(1 row)
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	min(user_id), sum(max_value_1)
+FROM
+	(SELECT user_id, max(value_1) as max_value_1 FROM users_table GROUP BY user_id) as bar;
+ min | sum
+---------------------------------------------------------------------
+   1 |  29
+(1 row)
+
 -- subqueries in FROM clause with LIMIT should be recursively planned
 SELECT
    user_id

src/test/regress/sql/subquery_basics.sql

@@ -1,9 +1,44 @@
 -- ===================================================================
 -- test recursive planning functionality
 -- ===================================================================
-
 SET client_min_messages TO DEBUG1;
 
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	user_id, value_1
+FROM
+	(SELECT user_id, value_1 FROM users_table) as foo
+ORDER BY 1 DESC, 2 DESC LIMIT 3;
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	sum(sel_val_1), sum(sel_val_2)
+FROM
+	(SELECT max(value_1) as  sel_val_1, min(value_2) as sel_val_2 FROM users_table GROUP BY user_id) as foo;
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	min(user_id), max(value_1)
+FROM
+	(SELECT user_id, value_1 FROM users_table) as foo;
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	min(user_id)
+FROM
+	(SELECT user_id, value_1 FROM users_table GROUP BY user_id, value_1) as bar;
+
+-- the subquery is safe to pushdown, should not
+-- recursively plan
+SELECT
+	min(user_id), sum(max_value_1)
+FROM
+	(SELECT user_id, max(value_1) as max_value_1 FROM users_table GROUP BY user_id) as bar;
+
 -- subqueries in FROM clause with LIMIT should be recursively planned
 SELECT
    user_id