Set correct cost data in Gather node added by force_parallel_mode.

We were just leaving the cost fields zeroes, which produces obviously bogus
output with force_parallel_mode = on.  With force_parallel_mode = regress,
the zeroes are hidden, but I wonder if they wouldn't still confuse add-on
code such as auto_explain.

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index ddf1109de76f4a75601af0d2721f13aa3a8ee5c0..796f564e4f88e608c6bf86c60c389911a5a2078e 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -343,7 +343,22 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
        gather->num_workers = 1;
        gather->single_copy = true;
        gather->invisible = (force_parallel_mode == FORCE_PARALLEL_REGRESS);
+
+       /*
+        * Ideally we'd use cost_gather here, but setting up dummy path data
+        * to satisfy it doesn't seem much cleaner than knowing what it does.
+        */
+       gather->plan.startup_cost = top_plan->startup_cost +
+           parallel_setup_cost;
+       gather->plan.total_cost = top_plan->total_cost +
+           parallel_setup_cost + parallel_tuple_cost * top_plan->plan_rows;
+       gather->plan.plan_rows = top_plan->plan_rows;
+       gather->plan.plan_width = top_plan->plan_width;
+       gather->plan.parallel_aware = false;
+
+       /* use parallel mode for parallel plans. */
        root->glob->parallelModeNeeded = true;
+
        top_plan = &gather->plan;
    }