| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | David Rowley <dgrowleyml(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Jeff Davis <pgsql(at)j-davis(dot)com>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, 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: | 2020-07-12 02:46:10 |
| Message-ID: | CA+hUKGKTeLS+q6rbbH=LMgEN9jJG425_6ow+_-fQ1gjOcO6tyg@mail.gmail.com |
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| Lists: | pgsql-docs pgsql-hackers |
On Sun, Jul 12, 2020 at 2:27 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> David Rowley <dgrowleyml(at)gmail(dot)com> writes:
> > hmm yeah. It's unfortunate, but I'm not sure how I'd have implemented
> > it differently. The problem is made worse by the fact that we'll only
> > release the memory for the hash table during ExecEndHashJoin(). If the
> > planner had some ability to provide the executor with knowledge that
> > the node would never be rescanned, then the executor could release the
> > memory for the hash table after the join is complete.
>
> EXEC_FLAG_REWIND seems to fit the bill already?
FWIW I have a patch that does exactly that, which I was planning to
submit for CF2 along with some other patches that estimate and measure
peak executor memory usage.
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