I don't know Postgres, and I just consider MySQL to be the leading best-in-class open source DB engine available. I realize that's debatable. But personally my

I don't know Postgres, and I just consider MySQL to be the leading best-in-class open source DB engine available. I realize that's debatable. But personally my mind is made up on that. I think relational-type queries are so common that any significant app will need them. For my own side project (meta64.com) I'm using JCR-SQL2, on Apache Oak jackrabbit, so I get to do lookups fairly easily, but it sure would be nice to have a full-blown ACID RDBMS engine sitting right there to use also, in the same engine.