I'd watch the JIRA for more details. Right now it says: anonymous wrote : The main issue here is that most databases (including mysql and oracle) do not index null values (if you think about it, you'll see why). The appropriate workaround for your case is probably to replace the unique constraint with a standard index on (KEY_, PROCESSDEFINITION_). | | The permanent fix is under discussion. | View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4034184#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...