Oh, and I assume you have to durably record the mapping between the short-hand notation (long) and the real transaction id. Essentially keep a reference as to where your index (the long) has reached so that, upon failure and recovery, you can continue counting from where you left off (or you risk generating a new mapping using the same counter before half a million years is up ;-). This durable recording is going to impose some overhead: every time you increment the counter you have to record it to disk . Plus, it probably needs to be managed transactionally too. Or did I miss something? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3976998#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...