| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jeff Davis <pgsql(at)j-davis(dot)com>, 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>, Justin Pryzby <pryzby(at)telsasoft(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Default setting for enable_hashagg_disk |
| Date: | 2020-07-25 17:07:37 |
| Message-ID: | CAH2-Wzm=RGSP7aa36_X_zvyx6oeAmbuoNJ8jnn-yF219RK0uoA@mail.gmail.com |
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| Lists: | pgsql-docs pgsql-hackers |
On Sat, Jul 25, 2020 at 9:39 AM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> "Peak Memory Usage: 1605334kB"
>
> Hash agg avoids spilling entirely (so the planner gets it right this
> time around). It even uses notably less memory.
I guess that this is because the reported memory usage doesn't reflect
the space used for transition state, which is presumably most of the
total -- array_agg() is used in the query.
--
Peter Geoghegan
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