[rabbitmq-discuss] Newcomer to Rabbit seeks exchange-type advice

Wed Jan 11 15:09:45 GMT 2012

Thank you, Alvaro.

Yes, I discovered that each consumer must have its own uniquely-named
queue.  I originally derived that queue name using a 128-bit UUID, but
discovered later that if I pass an empty string for the queue name in
the queue-declare, the server will generate a unique queue name for
me.  Perfect.

I appreciate your kind response.

I just downloaded the latest MEAP version of your book.  It's a
wonderful resource.  Thank you!

Mark

On Wed, Jan 11, 2012 at 1:28 AM, Alvaro Videla <videlalvaro at gmail.com> wrote:
> Hi Mark,
>
> Yes a topic exchange can be ideal when you need to "listen" based on several
> patterns. Also this exchange leaves the possibility open for new table
> names,
> You just have to think about the binding pattern that you want to use.
>
> Also keep in mind that if you want message X to arrive at consumer A and B
> then you need one separate queue per consumer bound to that exchange using a
> binding key that matches the routing key used when publishing message X.
> What this means is that messages are "fanout'ed" at the exchange, but once
> they arrive at a queue then messages are pulled out individually and once
> gone from the queue is not seen again.
>
> Cheers,
>
> Alvaro
>
> On Wed, Jan 11, 2012 at 1:46 AM, Mark Petrovic <mspetrovic at gmail.com> wrote:
>>
>> I think I have a solution, better than one based on a header exchange
>> or the scheme I outline below.
>>
>> It's basically this solution:
>>
>> http://www.rabbitmq.com/tutorials/tutorial-five-java.html
>>
>> where the routing keys are the table names.  This gives me a single
>> consumer queue bound to mulitple routing keys, which gets my job done.
>>
>>
>>
>> On Tue, Jan 10, 2012 at 2:20 PM, Mark Petrovic <mspetrovic at gmail.com>
>> wrote:
>> > Talking to myself here (I have no problem with that :-)), I think I
>> > have at least one solution to this.
>> >
>> > - Create a single exchange E
>> > - The Publisher P creates a channel with a single queue and routing
>> > key with the same names as the Table T in question.
>> > - Publisher publishes a message to channel
>> > - The Consumer C1 iterates over the table names T1 and T2 he cares
>> > about and binds his channel to queues and routing keys with the same
>> > name as the table name iterated over
>> > - The Consumer C1 then starts a thread for each of these queues, and
>> > whose run() method calls channel.basicConsume(queueName, autoAck,
>> > rabbitConsumer)
>> >
>> > where rabbitConsumer extends com.rabbitmq.client.DefaultConsumer.
>> >
>> > While this seems to work, and is a bit easier to understand how to
>> > program than header exchanges (if a header exchange would even work
>> > for me - I wonder), I dont' like the thread-per-queue I need to spawn
>> > to handle messages inbound for each queue.
>> >
>> > What would be nice is if I could call channel.basicConsume(autoAck,
>> > rabbitConsumer), which would read messages off all the queues that
>> > were bound to that channel.
>> >
>> > While I have something working, I'm not yet real thrilled with my
>> > programming model.
>> >
>> > Anybody?
>> >
>> > Thanks!
>> >
>> > On Tue, Jan 10, 2012 at 10:28 AM, Mark Petrovic <mspetrovic at gmail.com>
>> > wrote:
>> >> Hello.
>> >>
>> >> This note is longer than I thought it would be, but I do not believe
>> >> my situation is complicated.
>> >>
>> >> I am a RabbitMQ newcomer and am trying to identify which exchange type
>> >> to use for my application.
>> >>
>> >> I have a publisher P that needs to send messages about database table
>> >> updates.  A message will bear the name of a single table name,
>> >> followed by some opaque application data:
>> >>
>> >> Logically,
>> >>
>> >> message == tableName | somedata
>> >>
>> >> So consider a simplified database with three tables of interest:  T1,
>> >> T2, and T3.
>> >>
>> >> There are two consumers, C1 and C2.
>> >>
>> >> C1 needs to receive all messages concerning tables T1 and T2.
>> >>
>> >> C2 needs to receive all messages concerning tables T2 and T3.
>> >>
>> >> By implication, C1 and C2 must both receive messages about T2, where
>> >> their interests overlap.
>> >>
>> >> Ideally, I want to publish to a single exchange, and, therefore, my
>> >> consumers also bind to this same single exchange.  I say this because
>> >> in fact there are a lot more than three tables to treat - there are
>> >> almost 200.  A proliferation of exchanges per-table would be not good.
>> >>
>> >> I am considering a topic or header exchange.
>> >>
>> >> If a header exchange, I was thinking of the publisher P putting the
>> >> concerned table name in a "table header" and the consumers binding to
>> >> the exchange with an interest in receiving messages with a table
>> >> header value equal to T1, T2, or T3 (I believe x-match == any would be
>> >> appropriate when the consumer binds).  But some of my readings on
>> >> header exhchanges here
>> >>
>> >>
>> >> http://lists.rabbitmq.com/pipermail/rabbitmq-discuss/2011-January/010935.html
>> >>
>> >> suggest that header exchanges may not be as useful as maybe the name
>> >> suggests.  Maybe I'm being overly paranoid.
>> >>
>> >> And I consider topic exchanges because I know they admit messages
>> >> about T2 consumed by C1 still being available to C2.
>> >>
>> >> Would someone be kind enough to suggest approaches to discern which
>> >> type of exchange to use.
>> >>
>> >> Thank you very kindly.
>> >>
>> >> --
>> >> Mark
>> >
>> >
>> >
>> > --
>> > Mark
>>
>>
>>
>> --
>> Mark
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>
>

-- 
Mark