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

[Alvaro Videla]

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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>
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