Track sort direction in SortGroupClause

Functions make_pathkey_from_sortop() and transformWindowDefinitions(),
which receive a SortGroupClause, were determining the sort order
(ascending vs. descending) by comparing that structure's operator
strategy to BTLessStrategyNumber, but could just as easily have gotten
it from the SortGroupClause object, if it had such a field, so add
one.  This reduces the number of places that hardcode the assumption
that the strategy refers specifically to a btree strategy, rather than
some other index AM's operators.

Author: Mark Dilger <mark.dilger@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/E72EAA49-354D-4C2E-8EB9-255197F55330@enterprisedb.com

3 files changed, 10 insertions, 5 deletions

diff --git a/src/backend/optimizer/path/pathkeys.c b/src/backend/optimizer/path/pathkeys.c
index 035bbaa3856..7cf15e89b63 100644
--- a/src/backend/optimizer/path/pathkeys.c
+++ b/src/backend/optimizer/path/pathkeys.c
@@ -256,6 +256,7 @@ static PathKey *
 make_pathkey_from_sortop(PlannerInfo *root,
 						 Expr *expr,
 						 Oid ordering_op,
+						 bool reverse_sort,
 						 bool nulls_first,
 						 Index sortref,
 						 bool create_it)
@@ -279,7 +280,7 @@ make_pathkey_from_sortop(PlannerInfo *root,
 									  opfamily,
 									  opcintype,
 									  collation,
-									  (strategy == BTGreaterStrategyNumber),
+									  reverse_sort,
 									  nulls_first,
 									  sortref,
 									  NULL,
@@ -1411,6 +1412,7 @@ make_pathkeys_for_sortclauses_extended(PlannerInfo *root,
 		pathkey = make_pathkey_from_sortop(root,
 										   sortkey,
 										   sortcl->sortop,
+										   sortcl->reverse_sort,
 										   sortcl->nulls_first,
 										   sortcl->tleSortGroupRef,
 										   true);
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index c13586c537e..bd54a0d032d 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1896,6 +1896,7 @@ create_unique_plan(PlannerInfo *root, UniquePath *best_path, int flags)
 														 subplan->targetlist);
 			sortcl->eqop = eqop;
 			sortcl->sortop = sortop;
+			sortcl->reverse_sort = false;
 			sortcl->nulls_first = false;
 			sortcl->hashable = false;	/* no need to make this accurate */
 			sortList = lappend(sortList, sortcl);
diff --git a/src/backend/optimizer/plan/planagg.c b/src/backend/optimizer/plan/planagg.c
index afb5445b77b..dbcd3b9a0a0 100644
--- a/src/backend/optimizer/plan/planagg.c
+++ b/src/backend/optimizer/plan/planagg.c
@@ -48,7 +48,8 @@
 
 static bool can_minmax_aggs(PlannerInfo *root, List **context);
 static bool build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
-							  Oid eqop, Oid sortop, bool nulls_first);
+							  Oid eqop, Oid sortop, bool reverse_sort,
+							  bool nulls_first);
 static void minmax_qp_callback(PlannerInfo *root, void *extra);
 static Oid	fetch_agg_sort_op(Oid aggfnoid);
 
@@ -172,9 +173,9 @@ preprocess_minmax_aggregates(PlannerInfo *root)
 		 * FIRST is more likely to be available if the operator is a
 		 * reverse-sort operator, so try that first if reverse.
 		 */
-		if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, reverse))
+		if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, reverse, reverse))
 			continue;
-		if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, !reverse))
+		if (build_minmax_path(root, mminfo, eqop, mminfo->aggsortop, reverse, !reverse))
 			continue;
 
 		/* No indexable path for this aggregate, so fail */
@@ -314,7 +315,7 @@ can_minmax_aggs(PlannerInfo *root, List **context)
  */
 static bool
 build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
-				  Oid eqop, Oid sortop, bool nulls_first)
+				  Oid eqop, Oid sortop, bool reverse_sort, bool nulls_first)
 {
 	PlannerInfo *subroot;
 	Query	   *parse;
@@ -399,6 +400,7 @@ build_minmax_path(PlannerInfo *root, MinMaxAggInfo *mminfo,
 	sortcl->tleSortGroupRef = assignSortGroupRef(tle, subroot->processed_tlist);
 	sortcl->eqop = eqop;
 	sortcl->sortop = sortop;
+	sortcl->reverse_sort = reverse_sort;
 	sortcl->nulls_first = nulls_first;
 	sortcl->hashable = false;	/* no need to make this accurate */
 	parse->sortClause = list_make1(sortcl);