Message-ID: <4D7131FC.5030906@drivefaster.net>
Date: Fri, 04 Mar 2011 11:39:56 -0700
From: Dan Harris <fbsd@drivefaster.net>
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CC: pgsql-performance@postgresql.org
Subject: Re: Linux I/O schedulers - CFQ & random seeks
References: <536110.72154.qm@web26008.mail.ukl.yahoo.com>
	<4D712978.60504@databill.com>
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On 3/4/11 11:03 AM, Wayne Conrad wrote:
> On 03/04/11 10:34, Glyn Astill wrote:
> > I'm wondering (and this may be a can of worms) what peoples opinions 
> are on these schedulers?
>
> When testing our new DB box just last month, we saw a big improvement 
> in bonnie++ random I/O rates when using the noop scheduler instead of 
> cfq (or any other).  We've got RAID 10/12 on a 3ware card w/ 
> battery-backed cache; 7200rpm drives.  Our file system is XFS with 
> noatime,nobarrier,logbufs=8,logbsize=256k.  How much is "big?"  I 
> can't find my notes for it, but I recall that the difference was large 
> enough to surprise us.  We're running with noop in production right 
> now.  No complaints.
>
Just another anecdote, I found that the deadline scheduler performed the 
best for me.  I don't have the benchmarks anymore but deadline vs cfq 
was dramatically faster for my tests.  I posted this to the list years 
ago and others announced similar experiences.  Noop was a close 2nd to 
deadline.

XFS (noatime,nodiratime,nobarrier,logbufs=8)
391GB db cluster directory
BBU Caching RAID10 12-disk SAS
128GB RAM
Constant insert stream
OLAP-ish query patterns
Heavy random I/O