On 4/12/24 06:44, Tom Lane wrote:
Let me show current cases where users have a profit with this tiny improvement (see queries and execution results in query.sql): 1. 'Not optimised query text' — when we didn't consider group-by ordering during database development. 2. 'Accidental pathkeys' - we didn't see any explicit orderings, but accidentally, the planner used merge join that caused some orderings and we can utilise it. 3. 'Uncertain scan path' — We have options regarding which index to use, and because of that, we can't predict the optimal group-by ordering before the start of query planning. 4. 'HashAgg V/S GroupAgg' — sometimes, the GroupAgg strategy outperforms HashAgg just because we don't need any ordering procedure at all.If this patch were producing better results I'd be more excited about putting more work into it. But on the basis of what I'm seeing right now, I think maybe we ought to give up on it.
And the last thing here — this code introduces the basics needed to add more sophisticated strategies, like ordering according to uniqueness or preferring to set constant-width columns first in grouping.
-- regards, Andrei Lepikhov Postgres Professional
query.sql
Description: application/sql
