Do you really needs 16GB of heap? Have you done any performance testing to see what the actual memory requirements are? Cleaning up a 16GB heap, or even a 1GB young generation, will take time. And using the CMS collector will not reduce the young generation pauses. The CMS collector does pause the app twice for object marking; I have no idea how long it will take to mark a 16 GB heap. Ideally, you want the smallest heap possible that does not greatly negatively impact your performance. In this case I think you have run into the "more is not better" anti-pattern. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4235725#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...