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

From: Jeffrey W. Baker
Subject: Re: Query plan looks OK, but slow I/O - settings advice?
Date: ,
Msg-id: 1124434535.3257.7.camel@noodles
(view: Whole thread, Raw)
In response to: Query plan looks OK, but slow I/O - settings advice?  ("Roger Hand")
Responses: Re: Query plan looks OK, but slow I/O - settings advice?  (Dan Harris)
List: pgsql-performance

Tree view

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 Tue, 2005-08-16 at 10:46 -0700, Roger Hand wrote:
> The disks are ext3 with journalling type of ordered, but this was later changed to writeback with no apparent change
inspeed. 
>
> They're on a Dell poweredge 6650 with LSI raid card, setup as follows:
> 4 disks raid 10 for indexes (145GB) - sdc1
> 6 disks raid 10 for data (220GB) - sdd1
> 2 mirrored disks for logs - sdb1
>
> stripe size is 32k
> cache policy: cached io (am told the controller has bbu)
> write policy: write-back
> read policy: readahead

I assume you are using Linux 2.6.  Have you considered booting your
machine with elevator=deadline?  You can also change this at runtime
using sysfs.

These read speeds are not too impressive.  Perhaps this is a slow
controller.  Alternately you might need bigger CPUs.

There's a lot of possibilities, obviously :)  I'd start with the
elevator, since that's easily tested.

-jwb



pgsql-performance by date:

From: Christopher Browne
Date:
Subject: Re: Need for speed
From: Tom Lane
Date:
Subject: Re: Finding bottleneck