The abstracted module expose the underlying db object in `client` because the upgrade might need specific functionality that the interface doesn't have for example the `keys` method is not same between mongo and redis.

For example 

    RDB.keys('uid:*:notifications:flag',

`db.keys('uid:*:notifications:flag')` won't return the same thing when called on the mongo object. The keys method in mongo.js uses regex while redis uses glob patterns. If we can figure out how to implement the same functionality for keys I think we can remove it.