While I could use 2 servers machines with 2 identical structured databases and then presmably switch connection to use one DSN or the another, I am wandering if there is any other viable solution which would keep both databases on the same server, while application can safely switch between them.

It all depends what you mean by "database". With Oracle you have to be careful in your terminology, coming from SQL Server.

Um, you can have a single Oracle "database" (what SQL Server would call a "server") with many "schemas" (what SQL Server would call a "database") and connect to them from your application by connecting as a different user (because in Oracle "user" and "schema" are almost the same thing).

Does this correspond to your understanding?

I have not done any ODBC programming with Oracle so I won't speak to that.

- Colin