Save a few cycles in simple cases: no need to call cost_sort() when there

is no presorted path to compare with.

diff --git a/src/backend/optimizer/plan/planmain.c b/src/backend/optimizer/plan/planmain.c
index acc4eb5d9384dd6f5cad948dd51b5a038f1b5c79..4377359ddcc0ce50bbb73804cd15897d220be637 100644 (file)
--- a/src/backend/optimizer/plan/planmain.c
+++ b/src/backend/optimizer/plan/planmain.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planmain.c,v 1.53 2000/03/21 05:11:58 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/optimizer/plan/planmain.c,v 1.54 2000/03/24 21:40:43 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -174,7 +174,6 @@ subplanner(Query *root,
 {
        RelOptInfo *final_rel;
        Path       *cheapestpath;
-       Path            sort_path;              /* dummy for result of cost_sort */
        Path       *presortedpath;
 
        /*
@@ -288,21 +287,22 @@ subplanner(Query *root,
         * cheaper than doing an explicit sort on the cheapest-total-cost path.
         */
        cheapestpath = final_rel->cheapest_total_path;
-       cost_sort(&sort_path, root->query_pathkeys,
-                         final_rel->rows, final_rel->width);
-       sort_path.startup_cost += cheapestpath->total_cost;
-       sort_path.total_cost += cheapestpath->total_cost;
-
        presortedpath =
                get_cheapest_fractional_path_for_pathkeys(final_rel->pathlist,
                                                                                                  root->query_pathkeys,
                                                                                                  tuple_fraction);
        if (presortedpath)
        {
+               Path            sort_path;      /* dummy for result of cost_sort */
+
+               cost_sort(&sort_path, root->query_pathkeys,
+                                 final_rel->rows, final_rel->width);
+               sort_path.startup_cost += cheapestpath->total_cost;
+               sort_path.total_cost += cheapestpath->total_cost;
                if (compare_fractional_path_costs(presortedpath, &sort_path,
                                                                                  tuple_fraction) <= 0)
                {
-                       /* Found a better presorted path, use it */
+                       /* Presorted path is cheaper, use it */
                        root->query_pathkeys = presortedpath->pathkeys;
                        return create_plan(root, presortedpath);
                }