No black magic at all - just a simple callback to tell you once a buddy has fully joined a buddy group. :-) Regarding your exceptions, they look like standard lock acquisition timeouts. Your access pattern is very write-heavy. Write-heavy patterns will always have a lot of contention on write locks, and you should either increase your lock acquisition timeout (and deal with the waiting!) or catch the occasional exception and retry. Remember, caches are not designed to be write-heavy. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4152646#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...