Don't let stomp.py delete packet from ActiveMQ untill the whole packet is processed

Question

I am trying to get message from activemq using stomp.py and then doing some processing on it. But there is a case when that processing fails for certain messages and that message is lost.

How can I prevent the deletion of message untill the message is fully processed?

For example in my code when there is new entry in queue the on_message function will be called and the processing starts but if it is interrupted in between the message is lost. How do I stop it?

Here is my code:

conn = stomp.Connection([(host, 61613)])
conn.set_listener('ML', MyListener())
conn.start()
conn.connect('admin', 'admin', wait=True)
conn.subscribe(destination=/queue/someque, id=1, ack='auto')
print "running"
while 1:
    print 'waiting'
    time.sleep(2.5)

Here is my Listener class:

class MyListener(stomp.ConnectionListener):
    def on_message(self, headers, message):
        print headers
        print message
        do_something()

Thanks in advance.

Answer 1

The issue appears to be that you are using the 'auto' ack mode so the message will be acknowledged before delivery to the client by the broker meaning that even if you fail to process it, it's to late as it is already forgotten on the broker side. You'd need to use either 'client' ack or 'client-individual' ack mode as described in the STOMP specification. Using one of the client ack modes you control when a message or messages are actually acknowledged and dropped by the broker.