How to dequeue messages that were enqueued when app was offline

Question

I have 2 question. The following is the scenario -
I have 2 different process. Process A and Process B.
Process A enqueue's the message in the message queue.
Process B dequeue's the message from the message queue.
1) Process B shuts down for some time but Process A continues to enqueue the message in the queue. When Process B comes back live how to dequeue the messages in the message queue that were posted by Process A when Process B was offline?
2) The queue that I am using is multiple consumer queue as there needs to be more than 1 Process B to dequeue the message. The logic behind the design is if one of the process B dies the other process B can still continue to process. At the same time if 1 instance of Process B has picked up a message it should notify other Process B to not process the message.
I coudn't find any samples. Any help is greatly appreciated.

Answer 1

Hello,
The messages that process A enqueues and are not consumed while process B is down will remain in the queue until process B restarts.
It sounds as though you don't need to use a multi-consumer queue as all you appear to want to do is consume the messages as quickly as possible. Is that correct? If it is you could have multiple process Bs consuming messages from the same single consumer queue. Messages that one process is consuming will not be available to another and this is handled internally.
You can also have multiple processes consuming messages associated with the same consumer on a multi-cosnumer queue and the same applied.
Or you could have multiple processes on a multi-consumer queue associated with different subscribers which are all interested in the same message.
What you use depends on what your design requires but each message will be consumed only once in the case of a single consumer queue and only once per subscriber/recipient in a multi-consumer queue.
Thanks
Peter