The second solution also has the benefit of not actually touching the existing codebase. But, as someone who's done this kind of work (GL -> OpenGL), it's not as easy as it sounds.
in reply to Changing Modules in Bad Code
Problems you will encounter:
You might find it easier to take the existing Postgres module and rewriting its calls to use DBI. That way you know you have every possible call to Postgres covered and you don't have to worry about state maintenance and the like. Remember - all you have to change is the communication with the DB - the external stuff. You do not (and should not) have to change how Postgres works, internally. In fact, keeping it the same will improve your success potential.
- There isn't a 1-1 mapping between functions in the old and functions in the new.
- You'll probably have to write a bunch of state maintenance.
- Testing this will be absolutely imperative.
We are the carpenters and bricklayers of the Information Age.
Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.
Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.