I know that IBM has been doing some testing with JMS messaging backended by http://www-306.ibm.com/software/data/soliddb/ and I'm fairly certain that the same is being done by Oracle with their TimesTen and Coherence products.
I'm curious is any work has been done with JBoss Messaging on this front and if there is a good open source DB alternative to use for this test? [/url]
All new work is being carried out on JBM 2 which has a super fast journal, we'll also support JDBC but we don't recommend it for high performance.
For in memory only, you can also configure a null persistence manager so we don't really see any need to look at any in memory databases such as times ten.