Pawe? Piers'cionek wrote:
Hi,
I am new to the MQ stuff. Tried parsing through AMQP specs and QPID
docs and still don't get how to code this little two scenarios:
I have a single producer sending msgs to a queue with dynamic number
of consumers.
scenario A - all consumers get all messages
scenario B - consumers "compete" for messages - each msg gets consumed
by not more than one consumer.
Also how the picture changes for a durable version of scenario A -
where number of consumers is constant and I want to guarantee that all
messages get to all consumers even if one crashes and comes back after
some time.
My question is what exchange,queue types and options to use for what
scenario. Should I create a new exchange to handle scenario A or B?
TIA,
Pawel
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In scenario A, you want to create a queue per consumer (exclusive and
auto-delete). Each queue could be bound to a fanout exchange so it
receives a copy of every message sent to that exchange by the producer.
You would most likely want to create your own fanout exchange for this.
The durable version of scenario A is similar except that queues must be
created as durable (and not auto-delete) and the produced messages must
also be durable. If a consumer disconnects, it would have to remember
the name of the queue that it created so it could re-subscribe and pick
up where it left off.
There's another possible pattern for scenario A. Create a single queue
bound to a fanout exchange and have all consumers use browsing to
receive messages. Browsing means that messages are "peeked" at but not
consumed by the receiver and they remain for other receivers to view.
I'm not 100% sure but I think a "browsing" subscription uses
accept-mode: none and acquire-mode: not-acquired.
Scenario B is done with a single queue where the queue is not exclusive.
In this case, multiple consumers may subscribe to the queue and each
message will be consumed by exactly one consumer. A consumer may even
receive a message and reject it such that it can be consumed by a
different consumer.
In the multi-queue scenario, you will want to use a fanout exchange. In
the single queue cases, you can alternatively use a direct exchange
where the binding key is the name of the queue (or any constant string
known by the producer).
-Ted
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Project: http://qpid.apache.org
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