Re: posix_fadvise v22

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@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +