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Date: Fri, 11 Jan 2013 17:39:32 +0000
From: Fraser Adams <fraser.adams@blueyonder.co.uk>
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To: users@qpid.apache.org
Subject: Re: Instrumenting the Broker
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> Yes, with AMQP 0-10, the only time a producer indicates the destination of the message is when it actually sends the message. The message.transfer command includes the destination of the message, which is an exchange. A producer may send to various exchanges, simply by changing the destination in the message.transfer command with each message. As a result, from the broker's perspective, there's not really any way to look at a producer client and determine which exchange(s) it's sending to.
>
Thanks Andy that kind of makes sense.

I think that part of the confusion might stem from some of the higher 
level APIs, I've only really used JMS and qpid::messaging (I've steered 
well clear of qpid::client as recommended by Gordon and several others 
and I know plenty of people who've been bitten by qpid::client which 
makes me glad I did :-)).

So for qpid::messaging and JMS the model tends to be that one creates a 
connection, then one creates a session and in general in qpid::messaging 
one would create Senders specifying an address and in JMS similarly one 
would create a MessageProducer. So I guess that it's fairly easy to 
*assume* that the address (which in the case of a producer could just be 
the exchange name for something like amq.match) is associated with the 
Connection/Session.

if you normally do:

connection.open();
Session session = connection.createSession();
Sender sender = session.createSender("amq.match");

........
sender.send(message);
.........

it's easy to fall into that trap.

I guess that the alternate send which actually takes an address (e.g. 
the JMS MessageProducer |*send 
<http://docs.oracle.com/javaee/5/api/javax/jms/MessageProducer.html#send%28javax.jms.Destination,%20javax.jms.Message%29>*(Destination 
<http://docs.oracle.com/javaee/5/api/javax/jms/Destination.html> destination, 
Message 
<http://docs.oracle.com/javaee/5/api/javax/jms/Message.html> message)| ) 
is a closer analogue to the underlying AMQP message.transfer I guess 
that the higher level abstraction just acts as a cache for the real AMQP 
destinations.


Thanks again Andy I think that your explanation has helped clarify in my 
mind the transient association between Connection and Exchange even 
though I suspect in practice the vast majority of producer code is 
likely to be written in a way that retains what looks like a more 
sustained association, but that's only in the client runtime not in the 
broker.

Frase.


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