Trim ORDER BY/DISTINCT aggregate pathkeys in gather_grouping_paths

david-rowley · david-rowley · commit 4169850f0b6f · 2024-03-15T11:54:36.000+13:00
Similar to d8a2953, trim off any PathKeys which are for ORDER BY / DISTINCT aggregate functions from the PathKey List for the Gather Merge paths created by gather_grouping_paths(). These additional PathKeys are not valid to use after grouping has taken place as these PathKeys belong to columns which are inputs to an aggregate function and, therefore are unavailable after aggregation. Reported-by: Alexander Lakhin Discussion: https://postgr.es/m/cf63174c-8c89-3953-cb49-48f41f74941a@gmail.com Backpatch-through: 16, where 1349d27 was added
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
@@ -7320,6 +7320,17 @@ gather_grouping_paths(PlannerInfo *root, RelOptInfo *rel)
 {
 	ListCell   *lc;
 	Path	   *cheapest_partial_path;
+	List	   *groupby_pathkeys;
+
+	/*
+	 * This occurs after any partial aggregation has taken place, so trim off
+	 * any pathkeys added for ORDER BY / DISTINCT aggregates.
+	 */
+	if (list_length(root->group_pathkeys) > root->num_groupby_pathkeys)
+		groupby_pathkeys = list_copy_head(root->group_pathkeys,
+										  root->num_groupby_pathkeys);
+	else
+		groupby_pathkeys = root->group_pathkeys;
 
 	/* Try Gather for unordered paths and Gather Merge for ordered ones. */
 	generate_useful_gather_paths(root, rel, true);
@@ -7334,7 +7345,7 @@ gather_grouping_paths(PlannerInfo *root, RelOptInfo *rel)
 		int			presorted_keys;
 		double		total_groups;
 
-		is_sorted = pathkeys_count_contained_in(root->group_pathkeys,
+		is_sorted = pathkeys_count_contained_in(groupby_pathkeys,
 												path->pathkeys,
 												&presorted_keys);
 
@@ -7360,13 +7371,13 @@ gather_grouping_paths(PlannerInfo *root, RelOptInfo *rel)
 		 */
 		if (presorted_keys == 0 || !enable_incremental_sort)
 			path = (Path *) create_sort_path(root, rel, path,
-											 root->group_pathkeys,
+											 groupby_pathkeys,
 											 -1.0);
 		else
 			path = (Path *) create_incremental_sort_path(root,
 														 rel,
 														 path,
-														 root->group_pathkeys,
+														 groupby_pathkeys,
 														 presorted_keys,
 														 -1.0);
 
@@ -7375,7 +7386,7 @@ gather_grouping_paths(PlannerInfo *root, RelOptInfo *rel)
 									 rel,
 									 path,
 									 rel->reltarget,
-									 root->group_pathkeys,
+									 groupby_pathkeys,
 									 NULL,
 									 &total_groups);
 
