| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Cc: | pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Optimizing aggregates |
| Date: | 2016-08-31 16:10:50 |
| Message-ID: | 20160831161050.zgwx7f46ul3gu3xn@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2016-08-31 19:07:00 +0300, Heikki Linnakangas wrote:
> On 08/31/2016 06:51 PM, Andres Freund wrote:
> > I've first combined the projection for all the aggregates, ordered set,
> > or not, into one projetion. That got rid of a fair amount of overhead
> > when you have multiple aggregates. I attached an, probably out of date,
> > WIP version of that patch.
>
> A-ha, I also considered doing just that! I also considered a variant where
> we call ExecProject once for all non-ordered aggregates, and a separate
> ExecProject() for each ordered one. But just switching back to straight
> ExecEvalExprs seemed easier.
The issue is that might, I think, end up iteratively deforming the
underlying tuple. The projection machinery takes care of that, if we do
it in one go.
Greetings,
Andres Freund
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