Stale mids (message ids) in the :done key of queue

[frankitox]

Hello, maybe this is something someone already found while using workers.

The thing is, when I use queues sometimes I end up with stale mids (message ids) in the :done set of the queue. If I try to get the message status it returns nil. I suspect this happens when the worker processing the queue item crashes, but I'm not sure.

For now I have a little function to clean the stale mids.

(defn clean-done [conn-opts & qnames]
  (when (seq qnames)
    (doseq [qname qnames]
      (let [{:keys [done]} (car-mq/queue-status server-connection qname)]
        (doseq [mid done]
          (when-not (car/wcar conn-opts (car-mq/message-status qname mid))
            (car/wcar conn-opts (car/srem (car/key :carmine :mq qname :done) mid))))))))

From the library design perspective, there's any case where it makes sense to keep a mid with nil status in the :done set of the queue?

[ptaoussanis]

Hi there!

Yes, it's possible for items to temporarily sit the done state until GC'd (until the item is next picked up again for processing). More info in the message-queue ns docstring, and here.

Hope that helps!