Over at XAPRB blog there’s a great tutorial and discussion on using MySQL FEDERATED storage engine, which abstracts the data access layer among the different servers and allows you to access a table on a remote server as if you were using a local server with no explicit outbound connection to the remote MySQL server. There’s a pretty comprehensive article on using FEDERATED storage engine over on O’Reilly Network. There are quite a few findings about the FEDERATED tables over ay XARPB that will give you a better understanding of when the engine should be used and when it should not:
Rows retrieved from the remote storage don’t seem to be cached even for an instant. For example, if you issue a join against a remote table where the local table contains repeated data, the matching rows will be fetched over and over again from the remote table. One consequence is that if something updates the remote table while this is happening, you will see an inconsistent view of it, even within a single query.