Is there any issue with resending a message back to the Azure queue

Question

I've got a scheduler and some workers in Azure. The scheduler puts messages into a queue and the workers pull those messages and work on them. I've now just come into a scenario where I will need to move some data from table storage to our database once a certain threshold has been reached. These items need to be processed in order, oldest first. Once that threshold is met all the other items are processed in order. The current message that triggered the transfer needs to be stuffed at the end of the line and be reprocessed.

So, to the meat of my question...

Is it fine to simply resend the message to the queue as is or is there a potential for that to cause problems?

queueProvider.SendMessage(message);

A co-worker mentioned that he "though he might have read something about needing to do something special." I haven't seen anything to confirm his suspicions yet however so I thought I would pose the question here just to be safe.

Answer 1

The short answer is that it is fine. If you have a CloudQueueMessage, you can just send it to any queue (it is just a REST request at the end of the day). Every time you AddMessage(), it creates a new ID (might be same pop receipt but that doesn't matter). That being said, there are some things you might want to take care of and or investigate:

1. If you push a message onto one queue, pop it, and push to another queue or same queue, you should probably delete the first message off the queue. Merely popping it means that you have set the invisibility time out, but that it will reappear soon (and you now have identical message content on each queue). So, if I pop a message and immediately push it again, I now have 2 messages in the queue with identical content.
2. You can now update messages. This might be appropriate for you if you need ordering. You can indicate on the message itself in metadata or content what stage of processing it is in and you get some ordering here with a thoughtful implementation.

Answer 2

It is recommended that all logic inside the consumer of the queue be idempotent since a message can actually be picked up more than once. We have to keep in mind that the queue service guarantees that a message will be delivered, AT LEAST ONCE - so you could end up duplicating messages with this approach.