On Wed, Jul 27, 2022 at 6:46 AM David Rowley <dgrowle...@gmail.com> wrote:
> On Tue, 26 Jul 2022 at 19:39, Richard Guo <guofengli...@gmail.com> wrote: > > Also I'm wondering if it's possible to take into consideration the > > ordering indicated by existing indexes when determining the pathkeys. So > > that for the query below we can avoid the Incremental Sort node if we > > consider that there is an index on t(a, c): > > > > # explain (costs off) select max(b order by b), max(c order by c) from t > group by a; > > QUERY PLAN > > --------------------------------------------- > > GroupAggregate > > Group Key: a > > -> Incremental Sort > > Sort Key: a, b > > Presorted Key: a > > -> Index Scan using t_a_c_idx on t > > (6 rows) > > That would be nice but I'm not going to add anything to this patch > which does anything like that. I think the patch, as it is, is a good > meaningful step forward to improve the performance of ordered > aggregates. Concur with that. > There are other things in the planner that could gain from what you > talk about. For example, choosing the evaluation order of WindowFuncs. > Perhaps it would be better to try to tackle those two problems > together rather than try to sneak something half-baked along with this > patch. That makes sense. The patch looks in a good shape to me in this part. Thanks Richard
