So basically what this does is avoid locking the database while migrating? Obviously (and the README mentions this) the two releases have to be backwards- and forwards-compatible, so with this backend you avoid locking for other processes while migrating.

Very useful, especially for long migrations, but I would like to see a bit more detail about how this library achieves this, what the caveats are, etc.

EDIT: Never mind, there's a comprehensive "how it works" section farther down, I just needed to scroll far enough. This is very useful.