RE: Enterprise Manager warns of blocking on LGWR

There is no sensible way to bypass LGWR.  

LGWR writes redo buffer to the online logs (and to standby logs in some modes). Even if you don't archive your logs, an instance restart requires the online logs to clean up on deferred DBWR work recorded in the logs so that DBWR work is not the pacing activity.  

There are a few avenues of research to discover why LGWR might be identified as blocking.  

1. You could be wrapping logs with ARCH taking a long time to complete and make a log available to write in. A quick way to see if this is in the running is to look at your log history and see whether switches and last write times on logs correspond with the reported blocks.

I'd check that one first. IF it is add to the number of log groups in rotation (the default is tiny, I like 10 by pure preference unless I can prove I need more) and possibly increase the size of each log.  

In the old days some folks used to stash members of the online log groups in any nook or cranny they could find, and hilarity would ensue on multipurpose servers or disk farms when some batch process consumed near 100% of the i/o capability of the device that hosted some part of the online redo log. On slow devices, ARCH running could compete sufficiently with LGWR on a single device to slow LGWR down.  

mwf      

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Jeffrey Beckstrom
Sent: Thursday, December 07, 2017 3:52 PM To: oracle-l-freelists; oracle-db-l
Subject: Enterprise Manager warns of blocking on LGWR  

We are running EM 12.1.0.5. For the past several months, since upgrading our agent to 12.1.0.5, across various databases we have been receiving a blocking alert warning with the blocker being LGWR. By the time you log on the database directly or through Enterprise Manager, no blocking locks can be found. In fact, sometimes no active sessions are found or run quickly. After about 15+ minutes the alert clears.  

We do correctly receive the alert on user sessions that are causing a locking condition.  

Is there a way to bypass LGWR?

Jeffrey Beckstrom
Lead Database Administrator

Information Technology Department

Greater Cleveland Regional Transit Authority

1240 W. 6th Street
Cleveland, Ohio 44113  

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