JBoss uses a database to store JMS messages that are in transit and have not yet been delivered. By default, JMS is configured to use the Hypersonic database. I can't recall if there are other services that use this database also. If you are not using JMS, you can either remove the service, or ignore it. If you are using JMS, you will want to switch to another database. Other than that, a database would be used by an application deployed to JBoss. For example, I have a simple testing application that uses either MySQL or PostgreSQL as the database. Another example is the JBoss Portal, which is an application deployed to JBoss. It can use one of a variety of databases to store the portal information. Note that you can have multiple databases in use by the same instance of JBoss. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=3965595#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...