Skip site navigation (1) Skip section navigation (2)

Re: Linux I/O tuning: CFQ vs. deadline

From: Mark Wong <markwkm(at)gmail(dot)com>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: Greg Smith <greg(at)2ndquadrant(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, pgsql-performance(at)postgresql(dot)org, Albe Laurenz <laurenz(dot)albe(at)wien(dot)gv(dot)at>
Subject: Re: Linux I/O tuning: CFQ vs. deadline
Date: 2010-02-09 01:14:03
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Mon, Feb 8, 2010 at 9:49 AM, Josh Berkus <josh(at)agliodbs(dot)com> wrote:
>> That's basically what I've been trying to make clear all along:  people
>> should keep an open mind, watch what happens, and not make any
>> assumptions.  There's no clear cut preference for one scheduler or the
>> other in all situations.  I've seen CFQ do much better, you and Albe
>> report situations where the opposite is true.  I was just happy to see
>> another report of someone running into the same sort of issue I've been
>> seeing, because I didn't have very much data to offer about why the
>> standard advice of "always use deadline for a database app" might not
>> apply to everyone.
> Damn, you would have to make things complicated, eh?
> FWIW, back when deadline was first introduced Mark Wong did some tests
> and found Deadline to be the fastest of 4 on DBT2 ... but only by about
> 5%.  If the read vs. checkpoint analysis is correct, what was happening
> is the penalty for checkpoints on deadline was almost wiping out the
> advantage for reads, but not quite.
> Those tests were also done on attached storage.
> So, what this suggests is:
> reads:  deadline > CFQ
> writes: CFQ > deadline
> attached storage:  deadline > CFQ
> Man, we'd need a lot of testing to settle this.  I guess that's why
> Linux gives us the choice of 4 ...

I wonder what the impact is from the underlying RAID configuration.
Those DBT2 tests were also LVM striped volumes on top of single RAID0
LUNS (no jbod option).


In response to

pgsql-performance by date

Next:From: Scott CareyDate: 2010-02-09 03:50:06
Subject: Re: Linux I/O tuning: CFQ vs. deadline
Previous:From: Andres FreundDate: 2010-02-08 19:29:46
Subject: Re: [HACKERS] Re: Faster CREATE DATABASE by delaying fsync (was 8.4.1 ubuntu karmic slow createdb)

Privacy Policy | About PostgreSQL
Copyright © 1996-2018 The PostgreSQL Global Development Group