Volatile cache keys with Rails and Redis

Rails
1

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

2

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