[jboss-user] [EJB/JBoss] - MDB 'at most, once' delivery (Ack before onMessage)

[azda]

Is there any way to set up the MDB container to send an acknowledgment before it calls onMessage?  (I'm currently using EJB 3, but I don't think this is an EJB 3 specific question.  The app server is 5.0.1GA)

This seems like a fairly straight forward delivery pattern (guarantee the message was received, but not necessarily that any work was completed.  a.k.a 'at most, once').  I'm having problems figuring out if JEE supports this, or I'm just missing the right combination of settings.

Here are my requirements:
1.)  I don't need a transaction
2.)  A message should be processed 'at most, once' (it doesn't matter if the MDB acks and crashes before calling onMessage, thus loosing the message, as long as no duplicates are delivered)

I've set up: 
TransactionManagementType.BEAN, TransactionAttributeType.NOT_SUPPORTED for onMessage, acknowledgeMode=Auto-acknowledge, 
as well as MaxDeliveryAttempts=1 on the Queue

I read somewhere that this configuration would get me what I want (maybe for another app server?).   It doesn't.

1.) Ack isn't until onMessage completes
2.) If the app server crashes (I simulated by just killing the JVM), when it comes back up, the messages that were processing when the crash occurred, get re-delivered (even though I have MaxDeliveryAttempts at 1)!

The behavior of 2 is what I would expect with acknowledgeMode=Dups-ok-acknowledge.  I've read that this mode has the feature of not waiting till onMessage finishes to ack, but you can't guarantee when.  So you have to deal with the possibility of duplicates.

In Summary:  I'd rather not have to deal with detecting duplicates, and it seems easy enough to do, if the container would just ack before onMessage.  Is this possible, or am I just wishfully thinking?

-Az

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