Re: "LGWR any worker group" wait event

On 11/17/2017 04:27 PM, Jay.Miller_at_tdameritrade.com wrote:
>
> After upgrading one of our main transaction heavy RAC databases from
> 12.1 to 12.2 we had a small but noticeable decrease in overall
> performance. Looking at AWR reports I saw a new wait event popped up
> into the Top Timed Events which I had never seen before - "LGWR any
> worker group". Metalink isn't very helpful, just pointing to an
> IBM/AIX bug (we're on RedHat Linux running on x86).
>
> I can't find a definition of what the wait event signifies much less
> what might cause it.
>
> Anyone here familiar with it?
>
> Thanks!
>
> Jay Miller
>
> Sr. Oracle DBA
>

Hi Jay,

First, Metalink no longer exists. Nowadays, it's Your Oracle Support. And yes, it is becoming increasingly useless. They no longer publish any documents or papers about the inner workings of Oracle RDBMS. Since Oracle 12.1.0.1, Oracle is experimenting with multi-threaded log writer. They apparently cannot get it right. Since Oracle has now changed the system of versions, I would advise you to use single threaded LGWR, by setting "_use_single_log_writer=true". Oracle will probably get it right by the year 2525 and a support document which will document the behavior will be available few centuries after that. So, use patience my friend and don't use multi-threaded LGWR yet. There was a huge bug which would hang RAC databases every now and then and the cure provided by YOS was to revert back to single threaded LGWR. That killer bug is probably resolved by now, but  I doubt that the performance bugs have been resolved. For now, I would decline to be a beta tester for Oracle and revert back to the single threaded LGWR. Everything will be documented in the next book by Jonathan Lewis, should he decide to write one.

Regards

-- 
Mladen Gogala
Oracle DBA
http://mgogala.freehostia.com


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