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

From: Jeff Davis <pgsql(at)j-davis(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: 2010-02-16 21:34:11
Message-ID: 1266356051.20221.8.camel@monkey-cat.sm.truviso.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, 2010-02-08 at 09:49 -0800, Josh Berkus wrote:
> 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.

I also did some tests when I was putting together my Synchronized Scan
benchmarks:

http://j-davis.com/postgresql/83v82_scans.html

CFQ was so slow that I didn't include it in the results at all.

The tests weren't intended to compare schedulers, so I did most of the
tests with anticipatory (at least the ones on linux; I also tested
freebsd). However, I have some raw data from the tests I did run with
CFQ:

http://j-davis.com/postgresql/results/

They will take some interpretation (again, not intended as scheduler
benchmarks). The server was modified to record a log message every N
page accesses.

Regards,
	Jeff Davis


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