Re: POC: GROUP BY optimization

On 06/28/2018 06:52 PM, Teodor Sigaev wrote:
>> I'm afraid that's a misunderstanding - my objections did not really go
>> away. I'm just saying my claim that we're not messing with order of
>> grouping keys is not entirely accurate, because we do that in one
>> particular case.
>>
>> I still think we need to be careful when introducing new optimizations
>> in this area - reordering the grouping keys by ndistinct, ORDER BY or
>> whatever. In particular I don't think we should commit these patches
>> that may quite easily cause regressions, and then hope some hypothetical
>> future patch fixes the costing. Those objections still stand.
>
> Pls, have a look at https://commitfest.postgresql.org/18/1706/
> I tried to attack the cost_sort() issues and hope on that basis we can
> solve problems with 0002 patch and improve incremental sort patch.
>

OK, will do. Thanks for working on this!

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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