LGWR consumes 100% CPU

(Doc ID 813473.1)

Last updated on DECEMBER 06, 2016

Applies to:

Oracle Database - Enterprise Edition - Version 10.1.0.2 to 10.2.0.5 [Release 10.1 to 10.2]
Information in this document applies to any platform.
***Checked for relevance on 30-Jul-2012***
***Checked for relevance on 15-Mar-2016***


Symptoms

Log Writer Consumes 100% CPU with the instance going for Hang and the system goes for a freeze .

You might see the following symptoms :

--> The existing logged in user cannot do anything. New users will not be able to get connected.
--> The CPU on the DB Tier where the LGWR process exist shoots to 100%
--> When the CPU comes down, and no blocks are there with respect to LGWR, the problem goes away.
--> When the LGWR blocks the user sessions, system is in a freeze state and no new logins are allowed.   

        The following messages apper in the alert log .

WARNING: inbound connection timed out (ORA-3136)

--> Querying v$sessoions shows that LGWR is blocking some of the sessions

SQL> SELECT sid, blocking_session, username, blocking_session_status FROM v$session ORDER BY blocking_session ;

<Bug:2656965> LGWR SPINS AND CONSUMES ALL CPU AND INSTANCE HANGS

The workaround '_lgwr_async_io=false' to prevent lgwr from spinning did not fixed the issue . The problem may manifest even after _lgwr_async_io = false has been set and instance bounced .

You can view the file systems (and the options) mounted with the mount command :

 
#device                      device        mount       FS      fsck   mount      mount
#to mount                  to fsck         point       type    pass    at boot    options
/dev/dsk/c2t2d0s0   /dev/rdsk/c2t2d0s0       /d16      ufs        2       yes         -
/dev/dsk/c2t3d0s0   /dev/rdsk/c2t3d0s0       /d17      ufs        2        yes        -
........
.......



Cause

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