Re: Asynchonrous and synchronous messages on same channel

Tim Fox wrote:
>
> Hmmm.. The more I think about, I can see that we certainly don't need to
> wait for responses (i.e. we don't need message dispatcher) when sending
> unreliable messages, but I'm not 100% sure for reliable messages.
>
> When sending a reliable message to a topic, which has multiple
> subscriptions on different nodes, we persist the message if there are
> any durable subscriptions on the sending node, and then the message is
> cast across the group. So we already have the reliability guarantee
> before we cast the message.
>
> If the stack configuration we use can give us a strong enough
> reliability guarantee then i don't think we need to wait for any return
> values to "be sure" the messsage reached the nodes.

The stack essentially gives you the guarantee that a message will 
'eventually' reach all non-faulty members of a group. Which means, that 
if a member leaves (e.g. crashes) before it has received a message, it 
will never receive that message. If that message caused a modification 
to the shared group state, then the crashed member will get the state 
again when it re-joins, so that it has the same (shared) state as 
everyone else in the system. But there won't be any replaying of lost 
messages (a la persistent messages in JMS).

So when you publish to a JMS topic, don't you have the receivers send 
back acks for the received topics (similar to queues) ? If that's the 
case you probably need the MessageDispatcher, otherwise simply send 
messages via Channel.send()

-- 
Bela Ban
Lead JGroups / Manager JBoss Clustering Group
JBoss - a division of Red Hat

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