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From "Greg Vilardi" <>
Subject RE: What do I do with a heap dump? (OOM Permgen)
Date Fri, 02 Nov 2007 17:03:30 GMT
On 2 Nov 2007 at 7:24, Caldarale, Charles R wrote:

> > From: Peter Crowther [] 
> > Subject: RE: What do I do with a heap dump? (OOM Permgen)
> > 
> > As far as I know, public enemy #1 for eating PermGen space is 
> > still developers using the Singleton pattern in their code 
> > and not having listeners to null out the singleton instance 
> > when the webapp is undeployed.
> Analagous use of ThreadLocal is also a subtle contributor to the
> problem.  The offending references must be cleared at the end of
> processing of each request, since listeners don't have ready access to
> the thread pool.

Thank you for the pointers Peter. We do not have any Singletons in the 
application nor do we use ThreadLocal. However, we do not seem to be 
cleaning up the JDBC classes on redeploy. I'll install the 
SessionListener code that is mentionned in the references in Peter's 
reply. I'm also using the eval version of yourkit now to see what 
exactly is attached to each of the 52 WebAppClassLoaders in the dump.

I'll be back if I get stuck again further down the road. Thank you to 
all of the people who replied for the pointers and the tool 

Gregory H. Vilardi    631-752-2701x240
Project Manager / Lead Software Engineer           Fax: (631)752-3397
Recurrent Software Solutions, Inc.
1 Huntington Quadrangle, Suite 1C02, Melville, NY 11747 

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