| From: | Curt Sampson <cjs(at)cynic(dot)net> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | nickf(at)ontko(dot)com, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Ray Ontko <rayo(at)ontko(dot)com> |
| Subject: | Re: Script to compute random page cost |
| Date: | 2002-09-10 02:54:07 |
| Message-ID: | Pine.NEB.4.44.0209101153230.13186-100000@angelic.cynic.net |
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| Thread: | |
| Lists: | pgsql-hackers |
On Mon, 9 Sep 2002, Tom Lane wrote:
> Finally, I wouldn't believe the results for a moment if they were taken
> against databases that are not several times the size of physical RAM
> on the test machine, with a total I/O volume also much more than
> physical RAM. We are trying to measure the behavior when kernel
> caching is not helpful; if the database fits in RAM then you are just
> naturally going to get random_page_cost close to 1, because the kernel
> will avoid doing any I/O at all.
Um...yeah; another reason to use randread against a raw disk device.
(A little hard to use on linux systems, I bet, but works fine on
BSD systems.)
cjs
--
Curt Sampson <cjs(at)cynic(dot)net> +81 90 7737 2974 http://www.netbsd.org
Don't you know, in this new Dark Age, we're all light. --XTC
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