From: | "Albe Laurenz" <laurenz(dot)albe(at)wien(dot)gv(dot)at> |
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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 |
Message-ID: | D960CB61B694CF459DCFB4B0128514C203938157@exadv11.host.magwien.gv.at |
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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:
> http://insights.oetiker.ch/linux/fsopbench/
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
result.
Yours,
Laurenz Albe
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