Minor adjustments to WindowAgg startup cost code

This is a follow-on of 3900a02c9 containing some changes which I forgot
to commit locally before forming a patch with git format-patch.

Discussion: https://postgr.es/m/CAApHDvrB0S5BMv+0-wTTqWFE-BJ0noWqTnDu9QQfjZ2VSpLv_g@mail.gmail.com

diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 8b797e3b4621d32efb29f0e5b0bd3713d8efb648..d6ceafd51c5cdb499704adfab046830c4286338f 100644 (file)
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -2933,8 +2933,8 @@ get_windowclause_startup_tuples(PlannerInfo *root, WindowClause *wc,
                                 * NULLs are not allowed, but currently, there's no code to
                                 * error out if there's a NULL Const.  We'll only discover
                                 * this during execution.  For now, just pretend everything is
-                                * fine and assume that just the current row/range/group will
-                                * be needed.
+                                * fine and assume that just the first row/range/group will be
+                                * needed.
                                 */
                                end_offset_value = 1.0;
                        }
@@ -3055,15 +3055,6 @@ cost_windowagg(Path *path, PlannerInfo *root,
        startup_cost = input_startup_cost;
        total_cost = input_total_cost;
 
-       /*
-        * Estimate how many tuples we'll need to read from the subnode before we
-        * can output the first WindowAgg row.
-        */
-       startup_tuples = get_windowclause_startup_tuples(root, winclause,
-                                                                                                        input_tuples);
-
-       elog(DEBUG1, "startup_tuples = %g", startup_tuples);    /* XXX not for commit */
-
        /*
         * Window functions are assumed to cost their stated execution cost, plus
         * the cost of evaluating their input expressions, per tuple.  Since they
@@ -3124,6 +3115,9 @@ cost_windowagg(Path *path, PlannerInfo *root,
         * cost of the subnode, so we only need to do this when the estimated
         * startup tuples is above 1.0.
         */
+       startup_tuples = get_windowclause_startup_tuples(root, winclause,
+                                                                                                        input_tuples);
+
        if (startup_tuples > 1.0)
                path->startup_cost += (total_cost - startup_cost) / input_tuples *
                        (startup_tuples - 1.0);