| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Jeff Davis <pgsql(at)j-davis(dot)com> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, 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>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Default setting for enable_hashagg_disk |
| Date: | 2020-07-26 00:52:11 |
| Message-ID: | CAH2-Wznr3ntBOCktHqsBdniCLfhYZ48zj46uJ=VJQU8TP+k88A@mail.gmail.com |
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On Sat, Jul 25, 2020 at 5:31 PM Peter Geoghegan <pg(at)bowt(dot)ie> wrote:
> I'm glad that this better principled approach is possible. It's hard
> to judge how much of a problem this really is, though. We'll need to
> think about this aspect some more.
BTW, your HLL patch ameliorates the problem with my extreme "sorted vs
random input" test case from this morning [1] (the thing that I just
discussed with Tomas). Without the HLL patch the sorted case had 2424
batches. With the HLL patch it has 20. That at least seems like a
notable improvement.
[1] https://postgr.es/m/CAH2-Wz=ur7MQKpaUZJP=Adtg0TPMx5M_WoNE=ke2vUU=amdjPQ@mail.gmail.com
--
Peter Geoghegan
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