[jboss-user] [Performance Tuning] - Re: JBoss 4.05 don't release free memory - Out of Memory err

PeterJ do-not-reply at jboss.com
Thu Apr 17 10:39:38 EDT 2008

You mention monitoring JVM memory usage.  How are you doing that, using system tools? Unfortunately, that is not very helpful. You really need to monitory garbage collection data (e.g., -verbose:gc and similar JVM options) and examine that. That is the only thing that will tell you what is really going on.

Be aware that there will often be unused heap memory - the JVM will rarely use all of the memory that it asks for. For example, with a 1GB heap and a 200MB you generation, you will typically have at least 200MB of unused heap memory (unless you have a memory leak). The unused memory is a side0effect of the algorithm the JVM uses to determine when to do a full garbage collection.

See my presentation at http://www.cecmg.de/doc/tagung_2007/agenda07/24-mai/2b3-peter-johnson/index.html

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