Re: POC: GROUP BY optimization - Mailing list pgsql-hackers

From Teodor Sigaev
Subject Re: POC: GROUP BY optimization
Date
Msg-id a645a819-c0ab-243a-f903-ca9e0f1f5245@sigaev.ru
Whole thread Raw
In response to Re: POC: GROUP BY optimization  (Claudio Freire <klaussfreire@gmail.com>)
List pgsql-hackers
>> I don't see why not to generate all possible orderings (keeping only the
>> cheapest path for each pathkey variant) and let the optimizer to sort it
>> out.
> 
> I'm assuming costing the full N! possible orderings would be
> prohibitively expensive.

That's true, but for the first step we need to improve cost_sort and only then 
try to find the best pathkeys order by optimal way.

> - If the user requested that order, we assume it "somewhat
> subjectively better" (by giving it a slightly reduced cost).
I don't think so. It's not a SQL way - DB should define the optimal way to 
execute query.


-- 
Teodor Sigaev                                   E-mail: teodor@sigaev.ru
                                                    WWW: http://www.sigaev.ru/


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