[rabbitmq-discuss] Initial Questions on RabbitMQ and AMQP

Tue Oct 25 22:28:12 BST 2011

Mark

Queues are FIFO.

Think of email - under what circumstances would you expect ordering to
be preserved?

alexis

On Tue, Oct 25, 2011 at 10:25 PM, Matthias Radestock
<matthias at rabbitmq.com> wrote:
> Mark,
>
> On 25/10/11 21:51, Mark Petrovic wrote:
>>
>> 1) No ONCE-ONLY semantics. Messages may be sent twice by RabbitMQ to
>> the consumer(s)
>
> That only happens if something went wrong and, in effect, the message is
> "retried".
>
> Once-only / exactly-once are tricky to define, and impossible to implement
> if taken literally. There has been some previous discussion on the subject.
> A quick search of the archives brings up
>
>
> ../rabbitmq-server/scripts/rabbitmqctl delete_user test_user_no_perm
> Deleting user "test_user_no_perm" ...
> Error: {no_such_user,<<"test_user_no_perm">>}
> make[3]: [start_test_broker_node] Error 2 (ignored)
>
>
>>
>> 2) Unordered; not FIFO delivery
>>
>> I'm actually not certain (1) is a criticism of AMQP or Rabbit.  On its
>> face, it seems morally neutral, yet at the same time it appears to
>> make an important point.  Some interpretation from people in the know
>> here would still be helpful and much appreciated.
>>
>> As for (2), I recognize it as an oversimplication, after reading this
>> thread in this group:
>>
>>
>> http://groups.google.com/group/rabbitmq-discuss/browse_thread/thread/19066ba6f2944df8/f9d7d4bea18f2b5a?lnk=gst&q=fifo#
>>
>> The explanation by Matthias Radestock is helpful, but even after
>> reading his citation of the AMQP spec with respect to channels and
>> "single paths", I am still left with the sense that somehow AMQP
>> recognizes and codes to a world that is not quite so simple as "is- or
>> isNot-FIFO".  But I cannot put my finger on why, or what exactly is
>> being said.
>>
>> Would someone here be kind enough to talk about why section 4.7 of the
>> 0.9.1 spec reads ever so slightly tortured?
>>
>> And a short discussion of (1) would be very helpful, too.
>>
>> Thank you very kindly.
>>
>> Mark P.
>>
>
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