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From "Greg Vilardi" <gvila...@recurrentsoft.com>
Subject What do I do with a heap dump? (OOM Permgen)
Date Thu, 01 Nov 2007 23:11:14 GMT
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
-- 
Gregory H. Vilardi    631-752-2701x240     gvilardi@recurrentsoft.com
Project Manager / Lead Software Engineer           Fax: (631)752-3397
Recurrent Software Solutions, Inc.       http://www.recurrentsoft.com
1 Huntington Quadrangle, Suite 1C02, Melville, NY 11747 


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