| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Peter Geoghegan <pg(at)bowt(dot)ie>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Andres Freund <andres(at)anarazel(dot)de>, Bruce Momjian <bruce(at)momjian(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Default setting for enable_hashagg_disk |
| Date: | 2020-07-19 01:15:33 |
| Message-ID: | 32871.1595121333@sss.pgh.pa.us |
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Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> What is your opinion about pessimizing the HashAgg disk costs (not
> affecting HashAgg plans expected to stay in memory)? Tomas Vondra
> presented some evidence that Sort had some better IO patterns in some
> cases that weren't easily reflected in a principled way in the cost
> model.
Hm, was that in some other thread? I didn't find any such info
in a quick look through this one.
> That would lessen the number of changed plans, but we could easily
> remove the pessimization without controversy later if it turned out to
> be unnecessary, or if we further optimize HashAgg IO.
Trying to improve our cost models under-the-hood seems like a
perfectly reasonable activity to me.
regards, tom lane
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