def set(msg_id, suffix, value)
      with_failover { redis.set(key(msg_id, suffix), value) }
    end
def set(msg_id, suffix, value)
      with_failover { redis.set(key(msg_id, suffix), value) }
    end
unconditionally store a (key,value) pair with given <tt>suffix</tt> for given <tt>msg_id</tt>.