[jboss-user] [Performance Tuning] - Re: Cpu 100% and GC is running

Peter Johnson do-not-reply at jboss.com
Fri Jan 6 11:13:03 EST 2012

Peter Johnson [http://community.jboss.org/people/peterj] created the discussion

"Re: Cpu 100% and GC is running"

To view the discussion, visit: http://community.jboss.org/message/645086#645086

Why are you assuming that the daemon thread increase has anything to do with GC? Based on the GC data you provided, GCs happen every 3 seconds and are very short. The thread graph from VisualVM shows something completely different - the thread count is steady for a long time until suddenly it grows and then once again is steady. I think that there is another explanation for the growth in threads. It is almost as if, for example, a new EJB was accessed and the app server instantiated a number of them, each on its own thread.

I suggest that you take a thread dump, one before the daemon thread increase and another after, and examine the thread dump looking threads labelled "daemon".

By the way, the GC threads are always running. Take a thread dump and you should see 4 or 5 of them (based on your settings). They are there even when GC is not running. I hope that you have at least 4 cores - you should never set the number of GC threads to a larger number than the number of cores.

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