The reason I don't like the internal-int-external-UUID strategy is that all of your queries now require an extra join. It's no longer "select microblog.* where userid = ?" now it's "select microblog.*,user.id from microblog,user where microblog.userid = user.id and user.uuid = ?".

This may be practical from a storage standpoint but string-based indexes on an SSD are pretty damned efficient.