RE: log buffer size and log file syncs

From: CRISLER, JON A <JC1706_at_att.com>
Date: Tue, 1 May 2012 15:19:27 +0000
Message-ID: <9F15274DDC89C24387BE933E68BE3FD32551E4_at_MISOUT7MSGUSR9D.ITServices.sbc.com>

Red Hat Linux 5. We have async DG running but Real Time apply is also configured, and redo logs are mirrored. I believe LGWR is not starved for CPU given the overall conditions for the system, but I am finding some info that putting lgwr in a real-time OS priority would be a good thing. The default for _high_priority_processes is LMS*|VKTM but I have seen some Metalink notes about adding LGWR. I also saw a blog post that mentioned you discussed setting this parameter at a HOTSOS seminar, and this is something we are considering. Given all the CPU power in this server, and all the LMS processes, I don't this would pose a problem.

alter system set "_high_priority_processes"='LMS*|VKTM|LGWR' scope=spfile sid='*';

From: tanel_at_poderc.com [mailto:tanel_at_poderc.com] On Behalf Of Tanel Poder Sent: Monday, April 30, 2012 6:21 PM
To: CRISLER, JON A
Cc: oracle-l
Subject: Re: log buffer size and log file syncs

Which OS are you on? If it happens to be Solaris, then prstat -mLp PID would show the scheduling latency for LGWR. This would help to find out whether LGWR is CPU starved or not.... what load averages do you have?

Also, what does snapper say when ran on LGWR? If you have synchronous DG for example, then LGWR would wait for the LNS ack too in addition to the log file parallel write wait, before returning OK back to the committing session ...

Tanel.
On Mon, Apr 30, 2012 at 5:56 PM, CRISLER, JON A <JC1706_at_att.com<mailto:JC1706_at_att.com>> wrote: Interesting thoughts Tanel: in this case of this specific app, the majority of the work is made of up small commits to a handful of tables on a 6 node RAC cluster. I/O times are generally quite good, and with 32 cores per node the CPU and load average is very low. Its 11gR1 - I was wondering if some of the tweaks to put LGWR at "real time" priority that are mentioned for 10g also apply to 11g.

--
http://www.freelists.org/webpage/oracle-l

Received on Tue May 01 2012 - 10:19:27 CDT