My database server (h2) does not reliably support clustering yet; but I need to insure data redundancy. Can I mess up with Hibernate connections in such a way that every database connection would in fact be two connections to two different databases on two computers, seamlessly for the rest of the application? I only care about writes; reads can go to one database as far as I am concerned.
Well you could use Hibernate Shards project possibly.
But with Hibernate a Connection factory is one to one to a SessionFactory. So to point to two different databases you need two different SessionFactories.