Get rid of the AggressiveHeap setting - that setting sets a whole set of options (possibly overwriting some of the options you set before it). This option was primarily used by Sun for running the SPECjbb benchmark and is often not appropriate within a production environment. It looks like your young gen is taking up over 1/3 of the heap (probably due to AggressiveHeap being set). Try setting -XX:NewSize=400M and -XX:MaxNewSize=400M. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4233765#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...