I'm weighing in here on the comments about "Solving a problem that doesn't exist" - the database is quite loaded, and we have Redis in the stack anyway. The solution to this problem is any backend which creates unique numbers atomically; I happened to choose Redis because I'm interested in it technologically and I like the API.

It's worth mentioning that Rails doesn't encourage access to the underlying database features - and that stepping outside of the Rails/ActiveRecord results in features which are difficult to test and more difficult to maintain in the face of an ever changing API.

I don't care where the next atomic ID comes from, as long as it comes from a datastore that is fast, and that I can trust.