Questions[permgen](server)

I've been reading a lot about java memory management, garbage collecting et al and I'm trying to find the best settings for my limited memory (1.7g on a small ec2 instance) I'm wondering if there is a direct correlation between my code size and the permgen setting. According to sun:

The permanent generation is special because it holds data needed by the virtual machine to describe objects that do not have an equivalence at the Java language level. For example objects describing classes and methods are stored in the permanent generation.

To me this means that it's literally storing my class def'ns etc... Does this mean there is a direct correlation between my compiled code size and the permgen I should be setting? My whole app is about 40mb and i noticed we're using 256mb permgen. I'm thinking maybe we're using memory that could be better allocated to dynamic code like object instances etc...

i've a problem with our jmx monitoring. we monitor the perm gen of some jvms with jmx. but from time to time the name of the mbean changes from "PS Perm Gen" to "Perm Gen" or vice versa. it happens with a restart of the tomcat server, but not with every restart.

the jvm version is 1.5.0_16.

has anyone experienced this problem and perhaps has a solution?

I've run load against my web application for the past few days, and I've noticed that "Current Classes Loaded" viewed via JMX monitoring is continually increasing. It will go up and then back down, but the average amount of classes loaded is increasing linearly with time. At the beginning of load, "Current Classes Loaded" was only a few thousand. Now, however, "Current Classes Loaded" has reached 130,000+.

Is this normal? I know that classes will fill up PermGen memory, but it's not definitive whether or not PermGen memory is leaking.

Used: 
    65,124 kbytes
Committed: 
    65,536 kbytes
Max: 
    65,536 kbytes

The used number moves between 62k and 65k, but I haven't noticed any catastrophic failure yet on the server. My question, then, is twofold.

First, is this normal? If it isn't, will this eventually cause Tomcat to crash?

What is the underlying cause of a PermGen OutOfMemoryError in JBoss?

I am running JBoss AS 4.2.2 in my development environment, and this occurs after redeploying my web application a large number of times.

Christian Vest Hansen's blog gives JVM options that help a lot, but do not solve the problem completely:

-XX:+UseConcMarkSweepGC
-XX:+CMSPermGenSweepingEnabled
-XX:+CMSClassUnloadingEnabled
-XX:MaxPermSize=128m