|From:||Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>|
|To:||Jeff Davis <pgsql(at)j-davis(dot)com>|
|Cc:||Andres Freund <andres(at)anarazel(dot)de>, Tomas Vondra <tv(at)fuzzy(dot)cz>, pgsql-hackers(at)lists(dot)postgresql(dot)org, pgsql-hackers(at)postgresql(dot)org, Melanie Plageman <melanieplageman(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>|
|Subject:||Re: hashagg slowdown due to spill changes|
|Views:||Raw Message | Whole Thread | Download mbox | Resend email|
On Sat, Jun 13, 2020 at 11:48:09AM -0700, Jeff Davis wrote:
>On Fri, 2020-06-12 at 17:12 -0700, Andres Freund wrote:
>> Do you think we should tackle this for 13? To me 4cad2534da seems
>> like a
>> somewhat independent improvement to spillable hashaggs.
>We've gone back and forth on this issue a few times, so let's try to
>get some agreement before we revert 4cad2534da. I added Robert because
>he also seemed to think it was a reasonable idea.
I can't speak for Robert, but I haven't expected the extra projection
would be this high. And I agree with Andres it's not very nice we have
to do this even for aggregates with just a handful of groups that don't
need to spill.
In any case, I think we need to address this somehow for v13 - either we
keep the 4cad2534da patch in, or we tweak the cost model to reflect the
extra I/O costs, or we project only when spilling.
I'm not in a position to whip up a patch soon, though :-(
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
|Next Message||Tom Lane||2020-06-13 20:33:26||Re: Infinities in type numeric|
|Previous Message||Andrew Dunstan||2020-06-13 20:16:51||Re: jacana vs -Wimplicit-fallthrough|