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

From: "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at>
To: "Greg Smith *EXTERN*" <greg(at)2ndquadrant(dot)com>,<pgsql-performance(at)postgresql(dot)org>
Subject: Re: Linux I/O tuning: CFQ vs. deadline
Date: 2010-02-08 14:57:25
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Lists: pgsql-performance
Greg Smith wrote:
> Recently I've made a number of unsubstantiated claims that the deadline 
> scheduler on Linux does bad things compared to CFQ when running 
> real-world mixed I/O database tests.  Unfortunately every time I do one 
> of these I end up unable to release the results due to client 
> confidentiality issues.  However, I do keep an eye out for people who 
> run into the same issues in public benchmarks, and I just found one:  

That is interesting; particularly since I have made one quite different
experience in which deadline outperformed CFQ by a factor of approximately 4.

So I tried to look for differences, and I found two possible places:
- My test case was read-only, our production system is read-mostly.
- We did not have a RAID array, but a SAN box (with RAID inside).

The "noop" scheduler performed about as well as "deadline".
I wonder if the two differences above could explain the different

Laurenz Albe

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