I asked jboss support, and they said: "Yes, if multiple threads hit the same data at the same time they would each get a null and read from the database. To prevent this, you\'d need to use SERIALIZABLE isolation. But it does not scale, so unless you do have nodes hitting the same data at the same time extremely frequently, you would see worse overall performance." View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4215832#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...