Tomcat 6 Default Memory Allocation Settings

You need to provide a lot more information:

1) How much RAM is available on the box? Is Tomcat the only thing running?
2) Is this a 32bit or 64bit VM?
3) How many CPU's/cores are on this box?
4) What major version of the jdk are you running? 1.4, 5, or 6?

The answers to those questions will allow you to set boundaries for the heap.

Once you get past that, questions about the application may need to be answered - how many objects are long-lived (ie cache), and how many are short lived (less than 5 seconds before they go out of scope).

These questions will tell us what % of the heap can be used for Eden, and what percent needs to be used for the old generation.

Update

Well, if your Tomcat is long-running, then adding the '-server' flag would likely be beneficial. Given your constraints, unless you know your apps inside and out, it's probably best to leave it up to ergonomics to determine the best ratios and collector. Java tuning is much more an art than it is a science. Start here: http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html, then look for tools like GCHisto, and VisualGC to help you visualize what's going on inside the VM.

Phil,

You need to tune your JVM configuration. Take a look to the JMV configuration I'm using in my Tomcat server that is behaving very well under heavy traffic:

http://acevedoalberto.wordpress.com/2009/01/16/hello-world/

Alberto