On 06/29/2011 10:38 AM, Jiri Krutil wrote:
The default exchange is a direct exchange and the bindings are forced
to match exactly with the existing queue names. It is a workaround for
the fact that AMQP forces you to send to an exchange whether you want
to or not.
What is it you actually want to achieve? The only thing you can do by
sending messages to the default exchange is send them to a queue (or
have them dropped).
A Sender for the default exchange may be useful in case you want to send
to many different queues using one Sender and a different routing key
for each message. For instance when sending responses to reply-to queues
in a request-response pattern.
Ok, I understand. The assumption there is that senders are expensive to
create?
The reply-to address doesn't have to be a queue of course, to be
completely generic it should handle any exchange/routing-key pair (at
least in AMQP 0-10).
I'm working on a AMQP vendor-neutral C++ API and I'm trying to stay as
close to the concepts and ideas of the AMQP specs as possible. I guess
sending to the default exchange is a completely sane thing to do.
Yes, I can see that point of view.
One of the influences on Qpid's messaging API is the 1.0 specification.
There, to send a message you establish a link to a node on the broker.
This link is then used for any flow control and for some reliability
approaches.
My personal opinion is that the default exchange was a slightly clumsy
workaround for the fact that the versions of AMQP to date restricted
message 'sinks' to always be exchanges (and message 'sources' to always
be queues, though that's not related to the default exchange). The lack
of an explicit relationship between sender and sink was also an issue
(makes flow control more difficult for example).
The differences between the AMQP versions are significant. An API that
covers all of them would almost necessarily have to be at a higher level
of abstraction. That was the approach we took. We felt that the real
concern of the API was to control the inflow and outflow of messages and
all that this encompasses, but not to explicitly expose the mechanisms
as presented by underlying protocol versions.
I'd love to see your API if and when you are ready to publish it!
Let's say I create a Sender for queue A. It will actually point to the
default exchange with the routing key defaulting to A, right?
No, the messaging library resolves an address to a particular broker
entity. If the name matches a queue, then it assumes you want to send to
the queue. If the name matches an exchange then it assumes you want to
send to the exchange. If there is both a queue and an exchange with the
same name then at present you get an error and you have to explicitly
choose which one you want by indicating the node type in the address.
What happens if I use this sender to send a message with subject being
set to B? Will the message go to queue B?
No, it won't.
---------------------------------------------------------------------
Apache Qpid - AMQP Messaging Implementation
Project: http://qpid.apache.org
Use/Interact: mailto:[email protected]
