Variation in Max Heap size - Java in HP UX

[Rohit M]

Hi ,


I am using JBoss 4.2.3.GA server on a HP UX machine. Recently, our organization planned to buy a tool for performance monitoring of the enterprise applications. We have received reports that the maximum value of the heap is varying at times. As a direct result, I can see the CPU utilization (4 core, 3GHz machine) going up to 70% from a 30%. The funny thing is : actual heap utilization is almost constant (at 750MB)

I have attached an image of the heap variation. (In the picture of GC Heap, the green line represents the max heap while the red one marks the current utilization. We can notice that about the same time, the CPU utilization also increased.)


In the run.conf file (configuration file for JVM parameters), we have the following JVM parameters :

JAVA_OPTS="-server -Xms2048m -Xmx2048m -XX:PermSize=256m -XX:MaxPermSize=256m -XX:NewSize=640m -X:MaxNewSize=640m -XX:SurvivorRatio=16 -Dsun.rmi.dgc.client.gcInterval=3600000 -Dsun.rmi.dgc.server.gcInterval=3600000 -XX:+UseParallelGC -XX:ParallelGCThreads=4"

As we can see, the whole point of making the min and max heap values to be same (2GB) was to avoid the dynamic heap memory allocation by the OS. I am unable to understand why the max heap is varying even though the actual utilization remains the same.

Please let me know if I miss something.

I have posted this query in JBoss forums, but I've been asked to check with HP UX team.