MySQL and Postgres both have "replication" facilities, which probably do what you want to do, only they've been written and tested already, and are supported in a commercial capacity should you require it.

Further, if you're using BerkleyDB, you could very easily switch to an RDBMS by tying your data to SQL instead of a flat file. Your program will hardly notice the difference. There are several examples of this sort of thing floating around, one of which is in the MySQL and mSQL book from O'Reilly. You won't be able to use any of the fancy SQL features without rewriting parts, of course, but at least this is optional.