Re: log buffer size and log file syncs

Hi Jon,
Increasing LGWR priority would only help if it was currently starving for
CPU / or waiting too long in the CPU runqueue... Unfortunately on Linux
there's no easy way to measure this directly. If your load is low (let's
say only 10 on a 32 CPU machine) then I'd expect that LGWR priority change
isn't going to help much.

However, I don't like to fix a problem first and then see whether the
problem existed in first place (trial and error), that's why I asked for
extra information / hard evidence in form of LGWR's snapper output ...

Tanel.

On Tue, May 1, 2012 at 6:19 PM, CRISLER, JON A <JC1706@xxxxxxx> wrote:

>  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@xxxxxxxxxx [mailto:tanel@xxxxxxxxxx] *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@xxxxxxx> 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.****
>
> ** **
>

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