Re: POC: GROUP BY optimization

On 3/15/22 13:26, Tomas Vondra wrote:
> Thanks for the rebase. The two proposed changes (tweaked costing and
> simplified fake_var handling) seem fine to me. I think the last thing
> that needs to be done is cleanup of the debug GUCs, which I added to
> allow easier experimentation with the patch.
Thanks, I'm waiting for the last step.
>
> I probably won't remove the GUCs entirely, though. I plan to add a
> single GUC that would enable/disable this optimization. I'm not a huge
> fan of adding more and more GUCs, but in this case it's probably the
> right thing to do given the complexity of estimating cost with
> correlated columns etc.
Agree. Because it is a kind of automation we should allow user to switch
it off in the case of problems or manual tuning.

Also, I looked through this patch. It has some minor problems:
1. Multiple typos in the patch comment.
2. The term 'cardinality of a key' - may be replace with 'number of
duplicates'?

--
regards,
Andrey Lepikhov
Postgres Professional