Re: DBWR Tuning

From: Denis Do <nospam.denisdo_at_yahoo.com>
Date: Mon, 13 Dec 2004 03:51:43 GMT
Message-ID: <slrncrq4gd.17k.nospam.denisdo@denisdo.news.google.com>

>> Ref: Steve Adams - The Mysteries of DBWR Tuning
>>
>> We are trying to address the question "should we have multiple DBWR
>> processes?"

In Ora DB Perf Guide:
"Multiple db writer processes are highly recommended for systems with multiple CPUs (at least one db writer for every 8 CPUs) or multiple processor groups (at least as many db writers as processor groups). Based upon the number of CPUs and the number of processor groups, Oracle either selects an appropriate default setting for DB_WRITER_PROCESSES or adjusts a user-specified setting."

So, I would suggest to set at least 2 of them for start and see what happens. You definitely need more than one.
Since your OS does have async IO, you should not use IO Slaves, so both scans the buffer cache LRU and IO of those blocks will be performed by DBWRs - that is why you need more than one.

Cheers! Received on Sun Dec 12 2004 - 21:51:43 CST