On Wed, 13 Jul 2022 at 15:37, David Rowley <dgrowle...@gmail.com> wrote: > I'm just in this general area of the code again today and wondered > about the header comment for the preprocess_groupclause() function. > > It says: > > * In principle it might be interesting to consider other orderings of the > * GROUP BY elements, which could match the sort ordering of other > * possible plans (eg an indexscan) and thereby reduce cost. We don't > * bother with that, though. Hashed grouping will frequently win anyway. > > I'd say this commit makes that paragraph mostly obsolete. It's only > true now in the sense that we don't try orders that suit some index > that would provide pre-sorted results for a GroupAggregate path. The > comment leads me to believe that we don't do anything at all to find a > better order, and that's not true now.
I've just pushed a fix for this. David
