Re-fix wrong costing of Sort under Gather Merge.

robertmhaas · robertmhaas · commit 38fc54703ea4 · 2017-12-19T10:42:17.000-05:00
Commit dc02c7b changed this call to create_sort_path() to take -1 rather than limit_tuples because, at that time, there was no way for a Sort beneath a Gather Merge to become a top-N sort. Later, commit 3452dc5 provided a way for a Sort beneath a Gather Merge to become a top-N sort, but failed to revert the previous commit in the process. Do that. Report and analysis by Jeff Janes; patch by Thomas Munro; review by Amit Kapila and by me. Discussion: http://postgr.es/m/CAEepm=1BWtC34vUroA0Uqjw02MaqdUrW+d6WD85_k8SLyPiKHQ@mail.gmail.com
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
@@ -5059,7 +5059,7 @@ create_ordered_paths(PlannerInfo *root,
 											 ordered_rel,
 											 cheapest_partial_path,
 											 root->sort_pathkeys,
-											 -1.0);
+											 limit_tuples);
 
 			total_groups = cheapest_partial_path->rows *
 				cheapest_partial_path->parallel_workers;
