Re: DBWR Tuning

Giganews Newsgroups
Subject: Re: DBWR Tuning
Posted by:  Howard J. Rogers (h…@dizwell.com)
Date: Mon, 13 Dec 2004

wagen1…@yahoo.com wrote:
> Oracle9i 9.2.0.5 (64 bit)
> Solaris 2.9 (64 bit)
> RAID 0+1
> OLTP db
>
> Ref: Steve Adams - The Mysteries of DBWR Tuning
>
> We are trying to address the question "should we have multiple DBWR
> processes?"
>
> My understanding is that - If one does not see any wait events related
> to "free buffer waits" OR "write complete waits", DBWR tuning is not
> required and multiple DBWR processes is not required.
> Open to suggestions.
>
> Thanks
> wagen

Checkpoint incomplete messages in the alert log can indicate a sluggish
DBWR (it can also be a sluggish ARCH, as well... )

Same for redo retries and redo allocation waits. Could be silly sized
redo logs, could be too few log groups, could be poor ARCH performance.
Could be sluggish DBWR. Usually, you'd check other wait events to be
certain which of the possibles actually applies. So, for example, if I
have redo allocation problems, AND free buffer waits, I know faster hard
disks or more DBWRs could help. If I have checkpoint incomplete
messages, but no free buffer waits, then I'd suspect ARCH was mucking
around.

On the other hand, free buffer waits might not mean more DBWRs. It might
mean 'lose the RAID5'. Just as a for-example!

Regards
HJR

Replies

In response to

DBWR Tuning posted by wagen1…@yahoo.com on 12 Dec 2004