From: Tom Lane <tgl@sss.pgh.pa.us>
To: David Rowley <dgrowleyml@gmail.com>
cc: Peter Geoghegan <pg@bowt.ie>,
        "David G. Johnston" <david.g.johnston@gmail.com>,
        Stephen Frost <sfrost@snowman.net>, Jeff Davis <pgsql@j-davis.com>,
        Alvaro Herrera <alvherre@2ndquadrant.com>,
        Andres Freund <andres@anarazel.de>, Bruce Momjian <bruce@momjian.us>,
        Robert Haas <robertmhaas@gmail.com>,
        Justin Pryzby <pryzby@telsasoft.com>,
        Melanie Plageman <melanieplageman@gmail.com>,
        Tomas Vondra <tomas.vondra@2ndquadrant.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Default setting for enable_hashagg_disk
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Comments: In-reply-to David Rowley <dgrowleyml@gmail.com>
	message dated "Sat, 11 Jul 2020 17:00:22 +1200"
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Date: Sat, 11 Jul 2020 10:27:02 -0400
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David Rowley <dgrowleyml@gmail.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?

			regards, tom lane