parallel-incremental-sort.patch

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index b7723481b0..15c45202f9 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2719,6 +2719,8 @@ generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
 	{
 		Path	   *subpath = (Path *) lfirst(lc);
 		GatherMergePath *path;
+		bool		is_sorted;
+		int			presorted_keys;
 
 		if (subpath->pathkeys == NIL)
 			continue;
@@ -2727,6 +2729,33 @@ generate_gather_paths(PlannerInfo *root, RelOptInfo *rel, bool override_rows)
 		path = create_gather_merge_path(root, rel, subpath, rel->reltarget,
 										subpath->pathkeys, NULL, rowsp);
 		add_path(rel, &path->path);
+
+		/* consider incremental sort */
+		is_sorted = pathkeys_common_contained_in(root->sort_pathkeys,
+												 subpath->pathkeys, &presorted_keys);
+
+		if (!is_sorted && (presorted_keys > 0))
+		{
+			elog(WARNING, "adding incremental sort + gather merge path");
+
+			/* Also consider incremental sort. */
+			subpath = (Path *) create_incremental_sort_path(root,
+															rel,
+															subpath,
+															root->sort_pathkeys,
+															presorted_keys,
+															-1);
+
+			subpath->total_cost = 100.0;
+
+			path = create_gather_merge_path(root, rel, subpath, rel->reltarget,
+											subpath->pathkeys, NULL, rowsp);
+
+			path->path.total_cost = 120.0;
+
+			add_path(rel, &path->path);
+		}
+
 	}
 }