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From Filip Hanik - Dev Lists <>
Subject Re: What do I do with a heap dump? (OOM Permgen)
Date Fri, 02 Nov 2007 00:16:12 GMT works, and I'm sure there are others


Greg Vilardi wrote:
> Hello everyone. 
> My team and I are trying to develop a new web application and the 
> tomcat JVM is crashing every few days. We are deploying our separate 
> versions of the application several times per hour, and by looking at 
> jprobe, I see that each deployment of a webapp consumes 440kb of 
> PermGen space. This space does not seem to be released, although I've 
> only been monitoring this for 4 hours now. I have a heap dump from the 
> last crash, (courtesy of +XXHeapDumpOnOutOfMemoryError) and have taken 
> two memory dumps using jmap before and after a redeploy on an otherwise 
> quiescent JVM.
> Now, having done this, I've also looked at the dumps using jhat. There 
> seems to be a vast amount of data there, but I can't distill the 
> information I need out of it. I apologize if my Google-Fu is weak, but 
> I didn't find much real information on interpreting jhat data. 
> Preliminary examination of the jhat data does not show much of my 
> application or helper classes (mysql, jdbc).
> So, my questions are:
> How do I figure out what is in that 440kb per deployment?
> Is there an FM for me to R on how to interpret jhat data?
> What should I be looking for?
> How do I break this problem down further?
> The environment is:
> OS: Debian etch 2.6.21 kernel
> JVM: Sun Java 6 1.6.0-b105 Configured for use with jprobe and default 
> memory allocations. (This was done to try to make the problem easier to 
> reproduce/study.)
> Tomcat: 6.0.14 fronted via Apache 2.2.4 using mod_proxy_ajp.
> Database: MySQL 5.0.32 using the latest ConnectorJ.
> The application is a combination of JSP and servlets with some AJAX but 
> no Comet, Hibernate, &c. Apache and Tomcat were hand installed (not 
> from Debian packages).
> Any help that you can provide would be greatly appreciated.
> 	-Greg

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