From 945cb596cc0e62780994bd084eaea5355af85554 Mon Sep 17 00:00:00 2001 From: James Coleman Date: Fri, 30 Oct 2020 19:27:13 -0400 Subject: [PATCH v6 2/3] Add comments explaining where projections aren't necessary --- src/backend/optimizer/plan/planner.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c index 986d7a52e3..6989c5c0e3 100644 --- a/src/backend/optimizer/plan/planner.c +++ b/src/backend/optimizer/plan/planner.c @@ -7414,7 +7414,9 @@ apply_scanjoin_target_to_paths(PlannerInfo *root, * current reltarget is. We don't do this in the case where the * target is parallel-safe, since we will be able to generate superior * paths by doing it after the final scan/join target has been - * applied. + * applied. Since the target isn't parallel safe, we don't need to + * apply projections to the partial paths before building gather + * paths. */ generate_useful_gather_paths(root, rel, false); @@ -7567,7 +7569,10 @@ apply_scanjoin_target_to_paths(PlannerInfo *root, * if the relation is parallel safe, and we don't do it for child rels to * avoid creating multiple Gather nodes within the same plan. We must do * this after all paths have been generated and before set_cheapest, since - * one of the generated paths may turn out to be the cheapest one. + * one of the generated paths may turn out to be the cheapest one. We've + * already applied any necessary projections to the partial paths above so + * any Gather Merge paths will be able to make use of path keys in + * requested target. */ if (rel->consider_parallel && !IS_OTHER_REL(rel)) generate_useful_gather_paths(root, rel, false); -- 2.17.1