From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Peter Geoghegan <pg(at)bowt(dot)ie> |
Cc: | Andres Freund <andres(at)anarazel(dot)de>, Jeff Davis <pgsql(at)j-davis(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, David Rowley <dgrowleyml(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: | 2020-06-26 23:56:22 |
Message-ID: | 20200626235622.GE3337@momjian.us |
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Lists: | pgsql-docs pgsql-hackers |
On Fri, Jun 26, 2020 at 01:53:05PM -0700, Peter Geoghegan wrote:
> On Thu, Jun 25, 2020 at 1:36 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > 12 28164.865 ms
> >
> > fast ssd:
> > HEAD 92520.680 ms
> >
> > magnetic:
> > HEAD 183968.538 ms
> >
> > (no reads, there's plenty enough memory. Just writes because the age /
> > amount thresholds for dirty data are reached)
> >
> > In the magnetic case we're IO bottlenecked nearly the whole time.
>
> I agree with almost everything you've said on this thread, but at the
> same time I question the emphasis on I/O here. You've shown that
> spinning rust is about twice as slow as a fast SSD here. Fair enough,
> but to me the real story is that spilling is clearly a lot slower in
> general, regardless of how fast the storage subsystem happens to be (I
> wonder how fast it is with a ramdisk). To me, it makes more sense to
This blog entry shows ORDER BY using ram disk, SSD, and magnetic:
https://momjian.us/main/blogs/pgblog/2012.html#February_2_2012
It is from 2012, but I can re-run the test if you want.
--
Bruce Momjian <bruce(at)momjian(dot)us> https://momjian.us
EnterpriseDB https://enterprisedb.com
The usefulness of a cup is in its emptiness, Bruce Lee
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