RE: DBWR, Direct I/O and the Devil

  • From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx>
  • To: <don@xxxxxxxxx>, "Taylor, Chris David" <Chris.Taylor@xxxxxxxxxxxxxxx>
  • Date: Wed, 28 Nov 2007 16:07:40 -0500

Don,


I think you want both direct *and* async I/O configured, if your O/S and 
filesystem will support it.  In that case (with async i/o) you probably will 
only need 1 DBWR.  In addition to what Kevin has written in his blog, Steve 
Adams has some good stuff on his website:
http://www.ixora.com.au/tips/avoid_buffered_io.htm
http://www.ixora.com.au/tips/use_asynchronous_io.htm

And there are several others at:
http://www.ixora.com.au/tips/

It's old, but still relevant, I think.

-Mark

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Mark J. Bobak
Senior Database Administrator, System & Product Technologies
ProQuest
789 E. Eisenhower, Parkway, P.O. Box 1346
Ann Arbor MI 48106-1346
+1.734.997.4059  or +1.800.521.0600 x 4059
mark.bobak@xxxxxxxxxxxxxxx
www.proquest.com
www.csa.com

ProQuest...Start here. 


-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Don Seiler
Sent: Wednesday, November 28, 2007 2:39 PM
To: Taylor, Chris David
Cc: Oracle-L Freelists
Subject: Re: DBWR, Direct I/O and the Devil

On Nov 28, 2007 1:32 PM, Taylor, Chris David
<Chris.Taylor@xxxxxxxxxxxxxxx> wrote:
> Do you believe you have an I/O issue or are you just trying to "squeeze"
> more out of your I/O subsystem?

Right now I just want to know that I don't have some horribly obvious
(to everyone else) misconfiguration.  Obviously having a stable setup
is paramount, I'll worry about tuning again after that.  With my
recent rash of performance issues, I'm going through any and all
configuration changes that I made in the past 3 months and questioning
everything.

> Having played with db_writer_processes, I haven't really seen much
> improvement or negative impact from increasing/decreasing them.  But
> that is probably more due to the load (or lack thereof to notice any
> difference).

As I said, I'm all in favor of dropping down to 1, maybe back up to 2
if need be.  I just wanted to know if there's any concerns to be aware
of with the number of DBWR processes in direct vs. asynch I/O.

-- 
Don Seiler
http://seilerwerks.wordpress.com
ultimate: http://www.mufc.us
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