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List:       postgresql-general
Subject:    Re: [HACKERS] Optimizing aggregates
From:       Andres Freund <andres () anarazel ! de>
Date:       2016-08-31 16:10:50
Message-ID: 20160831161050.zgwx7f46ul3gu3xn () alap3 ! anarazel ! de
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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  I attached an, probably out of date,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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