Volatile cache keys with Rails and Redis

[bricker]

Does Rails automatically set an EXPIRE attribute on keys when working with Redis, or will an old key sit there forever if it's never manually cleared out? This is mostly a concern when using ActiveModel's "cache_key":

<%= cache @post do %>

The cache-key will be something like views/posts/744-20120613070958 . When the post is updated, and therefore gets a new cache-key, what happens to the old one? Will it just sit there forever? Do I need to add an `expires_in` option to every cache call, just to make sure it gets cleaned up every once in a while?

<%= cache @post, expires_in: 1.month do %>

Thanks,

Bryan

[Jeffrey Jones]

The idea is that your cache system should expire the oldest items in the
cache automatically when it hits its pre-configured size limit.