[jboss-user] [Performance Tuning] - Re: jboss cpu spike - GC?

Nikhil Mone do-not-reply at jboss.com
Wed Nov 28 06:14:27 EST 2012

Nikhil Mone [https://community.jboss.org/people/nikhilmone] created the discussion

"Re: jboss cpu spike - GC?"

To view the discussion, visit: https://community.jboss.org/message/778836#778836

> jboden wrote:
> Hi,
> I have a jboss 5.1 app with sun jdk 1.7.something. At night, it runs a large job and gobbles memory. The process gets to 2.5GB and never goes down, but I hear that's normal with heap space? But after a few days of this, I begin to see the cpu spike to 100% of one cpu for a few seconds, then go down. This happens every 5 seconds or so, probably GC?
> Using mostly a default run.bat, I have the jvm args set to:
> -Xrs -Xms256M -Xmx2048M -XX:MaxPermSize=256m -XX:+CMSClassUnloadingEnabled -XX:+UseConcMarkSweepGC 
>  -Dsun.rmi.dgc.client.gcInterval=3600000 -Dsun.rmi.dgc.server.gcInterval=3600000
>  -Dorg.jboss.resolver.warning=true
> Should we be doing something more specific? And if the GC keeps running that often even after the thread to do the nightly job has ended, do I have a memory leak somewhere? We do sometimes run out of memory, but maybe it needs Xmx of 4gb just to finish the job. 
> I'm going to up the memory anyway, but what clues do we look for to determine if there is a leak and/or better GC settings?
> Thank you very much!
> Jim
You can try adding below JAVA options in your "run.bat" to analyse what's wrong with GC :

 -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:<location of log directory>\gc.log

"gc.log" will contain the information about the collections, if you see a lot of gc activity (mostly FULL GC) when the issue occurs, then you would need to tune your memory/gc settings.

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