Acknowledge and message producers

Question

I can't seem to find a clear explanation of the difference, if any, between the CLIENT_ACKOWLEDGE and AUTO_ACKNOWLEDGE mode from the message producer's perspective. Is it because the server acknowledge is implicitly received when the publish() or send() methods return?
Thanks in advance.

Answer 1

That is an implementation specific question. For example in JBossMQ, a send is a send is a send unless the Session is transacted. In short, message sending behaves the same way regardless of what the acknowledge mode is on the Session. The acknowledge mode only comes into play on the other end.
Here is 1,000 foot view of how it works. You call send/publish, the IL calls a remote "send" method on the server passing the message as an argument. When that method has retuned successfully, the producer is done. Now the server has the message and it is its responsibility to get it to the proper consumer. So the server selectes a qualified consumer and calls a method on its instance of that client proxy passing in an array of Messages for delivery. The server, however, keeps a instance of that message until it receivs an explicit Acknowledge from the consuming client(s).
So, as I said, acknolwedgement only affect the consuming client. But that is just the way that JBossMQ currently implements it. Other providers are free to implement it anyway they wish so long as it fulfills the requirments of the spec. However, aside for peer-to-peer based JMS implementations, I cannot think of a reason to put acknowledgement code on the producer.
What can I do there? Can I keep the message and require the receiving client send me an acknowledgement? Ssounds good, but doesn't work becuase producers often come on line, send a few messages, and go off line. The message has to be stored for acknowledgement on the server so acknowledgment is typically a protocol between the consumer and the server that should not affect the producer.