Save calculated transitionSpace in Agg node.

This will be useful in the upcoming Hash Aggregation work to improve
estimates for hash table sizing.

Discussion: https://postgr.es/m/37091115219dd522fd9ed67333ee8ed1b7e09443.camel%40j-davis.com

src/backend/optimizer/plan/createplan.c

@@ -1644,6 +1644,7 @@ create_unique_plan(PlannerInfo *root, UniquePath *best_path, int flags)
 								 NIL,
 								 NIL,
 								 best_path->path.rows,
+								 0,
 								 subplan);
 	}
 	else
@@ -2096,6 +2097,7 @@ create_agg_plan(PlannerInfo *root, AggPath *best_path)
 					NIL,
 					NIL,
 					best_path->numGroups,
+					best_path->transitionSpace,
 					subplan);
 
 	copy_generic_path_info(&plan->plan, (Path *) best_path);
@@ -2257,6 +2259,7 @@ create_groupingsets_plan(PlannerInfo *root, GroupingSetsPath *best_path)
 										 rollup->gsets,
 										 NIL,
 										 rollup->numGroups,
+										 best_path->transitionSpace,
 										 sort_plan);
 
 			/*
@@ -2295,6 +2298,7 @@ create_groupingsets_plan(PlannerInfo *root, GroupingSetsPath *best_path)
 						rollup->gsets,
 						chain,
 						rollup->numGroups,
+						best_path->transitionSpace,
 						subplan);
 
 		/* Copy cost data from Path to Plan */
@@ -6192,8 +6196,8 @@ Agg *
 make_agg(List *tlist, List *qual,
 		 AggStrategy aggstrategy, AggSplit aggsplit,
 		 int numGroupCols, AttrNumber *grpColIdx, Oid *grpOperators, Oid *grpCollations,
-		 List *groupingSets, List *chain,
-		 double dNumGroups, Plan *lefttree)
+		 List *groupingSets, List *chain, double dNumGroups,
+		 Size transitionSpace, Plan *lefttree)
 {
 	Agg		   *node = makeNode(Agg);
 	Plan	   *plan = &node->plan;
@@ -6209,6 +6213,7 @@ make_agg(List *tlist, List *qual,
 	node->grpOperators = grpOperators;
 	node->grpCollations = grpCollations;
 	node->numGroups = numGroups;
+	node->transitionSpace = transitionSpace;
 	node->aggParams = NULL;		/* SS_finalize_plan() will fill this */
 	node->groupingSets = groupingSets;
 	node->chain = chain;

src/backend/optimizer/util/pathnode.c

@@ -2949,6 +2949,7 @@ create_agg_path(PlannerInfo *root,
 	pathnode->aggstrategy = aggstrategy;
 	pathnode->aggsplit = aggsplit;
 	pathnode->numGroups = numGroups;
+	pathnode->transitionSpace = aggcosts ? aggcosts->transitionSpace : 0;
 	pathnode->groupClause = groupClause;
 	pathnode->qual = qual;
 
@@ -3036,6 +3037,7 @@ create_groupingsets_path(PlannerInfo *root,
 	pathnode->aggstrategy = aggstrategy;
 	pathnode->rollups = rollups;
 	pathnode->qual = having_qual;
+	pathnode->transitionSpace = agg_costs ? agg_costs->transitionSpace : 0;
 
 	Assert(rollups != NIL);
 	Assert(aggstrategy != AGG_PLAIN || list_length(rollups) == 1);

src/include/nodes/pathnodes.h

@@ -1663,6 +1663,7 @@ typedef struct AggPath
 	AggStrategy aggstrategy;	/* basic strategy, see nodes.h */
 	AggSplit	aggsplit;		/* agg-splitting mode, see nodes.h */
 	double		numGroups;		/* estimated number of groups in input */
+	Size		transitionSpace;	/* for pass-by-ref transition data */
 	List	   *groupClause;	/* a list of SortGroupClause's */
 	List	   *qual;			/* quals (HAVING quals), if any */
 } AggPath;
@@ -1700,6 +1701,7 @@ typedef struct GroupingSetsPath
 	AggStrategy aggstrategy;	/* basic strategy */
 	List	   *rollups;		/* list of RollupData */
 	List	   *qual;			/* quals (HAVING quals), if any */
+	Size		transitionSpace;	/* for pass-by-ref transition data */
 } GroupingSetsPath;
 
 /*

src/include/nodes/plannodes.h

@@ -813,6 +813,7 @@ typedef struct Agg
 	Oid		   *grpOperators;	/* equality operators to compare with */
 	Oid		   *grpCollations;
 	long		numGroups;		/* estimated number of groups in input */
+	Size		transitionSpace;	/* for pass-by-ref transition data */
 	Bitmapset  *aggParams;		/* IDs of Params used in Aggref inputs */
 	/* Note: planner provides numGroups & aggParams only in HASHED/MIXED case */
 	List	   *groupingSets;	/* grouping sets to use */

src/include/optimizer/planmain.h

@@ -54,8 +54,8 @@ extern Sort *make_sort_from_sortclauses(List *sortcls, Plan *lefttree);
 extern Agg *make_agg(List *tlist, List *qual,
 					 AggStrategy aggstrategy, AggSplit aggsplit,
 					 int numGroupCols, AttrNumber *grpColIdx, Oid *grpOperators, Oid *grpCollations,
-					 List *groupingSets, List *chain,
-					 double dNumGroups, Plan *lefttree);
+					 List *groupingSets, List *chain, double dNumGroups,
+					 Size transitionSpace, Plan *lefttree);
 extern Limit *make_limit(Plan *lefttree, Node *limitOffset, Node *limitCount);
 
 /*