Re: hashagg slowdown due to spill changes

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tv(at)fuzzy(dot)cz>
Cc: pgsql-hackers(at)lists(dot)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org, Melanie Plageman <melanieplageman(at)gmail(dot)com>
Subject: Re: hashagg slowdown due to spill changes
Date: 2020-06-12 22:29:08
Message-ID: 15822bc5cf4324068bb4230631130f6522ed9c21.camel@j-davis.com
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On Fri, 2020-06-12 at 14:37 -0700, Andres Freund wrote:
> I don't see why it's ok to force an additional projection in the very
> common case of hashaggs over a few rows. So I think we need to
> rethink
> 4cad2534da6.

One possibility is to project only spilled tuples, more similar to
Melanie's patch from a while ago:

https://www.postgresql.org/message-id/CAAKRu_aefEsv+UkQWqu+ioEnoiL2LJu9Diuh9BR8MbyXuZ0j4A@mail.gmail.com

Which makes sense, but it's also more code.

Regards,
Jeff Davis

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