[jboss-user] [Performance Tuning] - Re: JBoss Performance Tuning

[jerrynolan]

You can also use jmap with the -heap option to check your permgen.
It will give you a listing of different areas of the jvm memory footprint, permgen is at the bottom. It's a quick way to take a look.
You run it with jmap -heap <jboss jvm pid>
For instance:

/usr/jdk1.5/bin/jmap -heap 7302
  | ...
  | Perm Generation:
  |    capacity = 134217728 (128.0MB)
  |    used     = 79881104 (76.18055725097656MB)
  |    free     = 54336624 (51.81944274902344MB)
  |    59.51606035232544% used
  | 
On this box min and max permgen is set to 128M. If you don't have them both set to the same value (aka pre-allocated), jmap will tell you what value was being used when you ran the command - the value will be "capacity".

In my case, someone had set the box to 300M for permgen. Checking with jmap -heap over a weeks period made me realize that 128M was enough for this box.



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