Our rule is thumb is to not set the heap larger than the amount of RAM on the machine. Note that the Sun JVM will never use all of the heap allocated due to its algorithm for determining when to do a major collection, so even in a 1GB system setting the heap to 1GB still leaves enough free RAM available to run the OS and the basic services. Also, don't forget to set the young generation to 1/3 or 1/4 the size of the heap. Finally, don't allocate a larger heap than what you really need. If you have a 64bit machine with 32GB of RAM, setting the heap to 32GB might seem like a good thing to do, until you hit your first major collection and realize that it is taking several minutes. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4005003#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...