Re: "LGWR any worker group" wait event
- From: Mladen Gogala <gogala.mladen@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 17 Nov 2017 16:53:00 -0500
On 11/17/2017 04:27 PM, Jay.Miller@xxxxxxxxxxxxxxxx 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
Other related posts:
