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LGWR consumes 100% CPU (Doc ID 813473.1)

Last updated on FEBRUARY 02, 2022

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 10.1 to 10.2]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.


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 ;


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 :


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