JBM treated transactional messages like this: Each transaction has a in memory list to hold all its messages. When a transaction is being committed, it put those messages to the Queue for delivery. After the tx is committed, the associated list should be GCed. The queue has paging functionality to prevent its memory from being used up. The fullSize is used to limit the num of messages that are hold in memory. I think that will explain the situation you have. View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4255912#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...