postgres.git / summary / log / commit / refs

commit    af7d270dd3c7523dad023f5761f630daa7fb2730
Author:   David Rowley <drowley@postgresql.org>
Date:     Wed Aug 17 23:32:55 2022 +0000

    Fix hypothetical problem passing the wrong GROUP BY pathkeys
    
    1349d2790 changed things to make the planner request that the
    query_pathkeys contain pathkeys for any ORDER BY / DISTINCT aggregates.
    Some code added prior to that commit in db0d67db2 made it so the order
    that the pathkeys appear in the group_pathkeys could be changed so that
    the GROUP BY could be executed in a more optimal order which minimized
    sort comparisons.  1349d2790 had to make sure that the pathkeys for any
    ORDER BY / DISTINCT aggregates remained at the end of the groupby_pathkeys
    and wasn't reordered, so some code was added to
    add_paths_to_grouping_rel() to first strip off any pathkeys belonging to
    ORDER BY / DISTINCT aggregates before passing to the function to optimize
    the order of the group_pathkeys.
    
    It seems I dropped the ball in 1349d2790 and mistakenly used the untouched
    PlannerInfo.group_pathkeys to pass to get_useful_group_keys_orderings()
    instead of the version that had the aggregate pathkeys removed.  It was
    only the code path that was handling creating paths for
    partially_grouped_rel which made this mistake.  In practice, we'll never
    have any extra pathkeys to strip off when processing
    partially_grouped_rel as that's only used when considering partial
    paths, which we never do when there are ORDER BY / DISTINCT aggregates.
    So this is just a hypothetical bug, not a live bug.  We already have the
    correct pathkeys determined, so it's of no extra cost to pass the
    correct variable.
    
    Reported-by: Justin Pryzby
    Discussion: https://postgr.es/m/20220817015755.GB26426@telsasoft.com


 src/backend/optimizer/plan/planner.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index bf45b498ba3..b781080dbac 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -6637,10 +6637,7 @@ add_paths_to_grouping_rel(PlannerInfo *root, RelOptInfo *input_rel,
 				ListCell   *lc2;
 				Path	   *path = (Path *) lfirst(lc);
 				Path	   *path_original = path;
-
 				List	   *pathkey_orderings = NIL;
-
-				List	   *group_pathkeys = root->group_pathkeys;
 				List	   *group_clauses = parse->groupClause;
 
 				/* generate alternative group orderings that might be useful */


[parent: a340359a4f9b]