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Re: posix_fadvise v22

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Greg Smith <gsmith(at)gregsmith(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Gregory Stark <stark(at)enterprisedb(dot)com>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)oss(dot)ntt(dot)co(dot)jp>, Postgres <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: posix_fadvise v22
Date: 2009-01-02 20:43:41
Message-ID: 200901022043.n02Khfa03040@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Greg Smith wrote:
> On Fri, 2 Jan 2009, Tom Lane wrote:
> 
> > ISTM that you *should* be able to see an improvement on even
> > single-spindle systems, due to better overlapping of CPU and I/O effort.
> 
> The earlier synthetic tests I did:
> 
> http://archives.postgresql.org/pgsql-hackers/2008-09/msg01401.php
> 
> Showed a substantial speedup even in the single spindle case on a couple 
> of systems, but one didn't really seem to benefit.  So we could theorize 
> that Robert's test system is more like that one.  If someone can help out 
> with making a more formal test case showing this in action, I'll dig into 
> the details of what's different between that system and the others.

I think for an I/O-bound workload on a single drive system you would
need a drive that did some kind of tagged queuing (reordering/grouping)
of requests to see a benefit from the patch.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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