Re: Query plan looks OK, but slow I/O - settings advice?

From: Dan Harris
Subject: Re: Query plan looks OK, but slow I/O - settings advice?
Date: ,
Msg-id: E0CDF4BA-278D-4EFA-9438-A5BA4802C158@drivefaster.net
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In response to: Re: Query plan looks OK, but slow I/O - settings advice?  ("Jeffrey W. Baker")
Responses: Re: Query plan looks OK, but slow I/O - settings advice?  (Michael Stone)
List: pgsql-performance

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Query plan looks OK, but slow I/O - settings advice?  ("Roger Hand", )
 Re: Query plan looks OK, but slow I/O - settings advice?  ("Jeffrey W. Baker", )
  Re: Query plan looks OK, but slow I/O - settings advice?  (Dan Harris, )
   Re: Query plan looks OK, but slow I/O - settings advice?  (Michael Stone, )
 Re: Query plan looks OK, but slow I/O - settings advice?  (Gavin Sherry, )
 Re: Query plan looks OK, but slow I/O - settings advice?  ("Roger Hand", )

On Aug 19, 2005, at 12:55 AM, Jeffrey W. Baker wrote:

> On Tue, 2005-08-16 at 10:46 -0700, Roger Hand wrote:
>   Have you considered booting your
> machine with elevator=deadline?

Although I'm not the OP for this problem, I thought I'd try it out.
WOW.. this should be in a Pg tuning guide somewhere. I added this to
my server tonight just for kicks and saw a pronounced improvement in
IO performance.  Thank you very much for mentioning this on the list.

I didn't have a long enough maintenance window to do solid
benchmarking, but I can say for certain that the change was
noticeable, especially in VACUUM operations.

Specs for the server:

PG 8.0.1
Linux 2.6.12-3 kernel
4xOpteron 2.2
12GB RAM
16-drive RAID 10
XFS mounted with noatime
pg_xlog on separate RAID controller

-Dan



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