| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
| Cc: | Jeff Davis <pgsql(at)j-davis(dot)com>, David Rowley <dgrowleyml(at)gmail(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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: | 2020-07-27 20:01:11 |
| Message-ID: | CAH2-WzmWPEjvko_6NJm+wvPXT6NS2FtLb=anH2AEkedYEDecCA@mail.gmail.com |
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| Lists: | pgsql-docs pgsql-hackers |
On Mon, Jul 27, 2020 at 12:52 PM Alvaro Herrera
<alvherre(at)2ndquadrant(dot)com> wrote:
> On 2020-Jul-27, Peter Geoghegan wrote:
> > The v4-0001-Remove-hashagg_avoid_disk_plan-GUC.patch changes are
> > surprisingly complicated. It would be nice if you could take a look at
> > that aspect (or confirm that it's included in your review).
>
> I think you mean "it replaces surprisingly complicated code with
> straightforward code". Right? Because in the previous code, there was
> a lot of effort going into deciding whether the path needed to be
> generated; the new code just generates the path always.
Yes, that's what I meant.
It's a bit tricky. For example, I have removed a redundant
"cheapest_total_path != NULL" test in create_partial_grouping_paths()
(two, actually). But these two tests were always redundant. I have to
wonder if I missed the point. Though it seems likely that that was
just an accident. Accretions of code over time made the code work like
that; nothing more.
--
Peter Geoghegan
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