Thanks guys for the responses. Can I move the question a bit? As I said we're running a JBoss Cluster using MySQL 5.0.51 as the underlying JMS data store. I'm trying to send 5000 messages (20k each) through the system - with a sender and receiver client. Lets call the 2 JBoss instances Jboss1 and Jboss2 and the two MySQL data notes mysql1 and mysql2 Jboss1 has a datasource pointing to mysql1; Jboss2 points to mysql2. My sender app is connecting to the JNDI on Jboss1 and getting a ClusteredConnectionFactory, The receiver is doing the same, but on Jboss2. So, what I see is that for normal operation, messages go into the cluster via Jboss1/mysql2, but get pulled off via Jboss2/mysql2 But... when I sent 5000 messages in, I'm seeing 100-200 messages getting stuck and not being picked up by the receiver process. Any ideas? Thanks. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4207452#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...