[rabbitmq-discuss] RabbitMQ and AMQP questions

[ae6rt]

Good day.  I have read the RabbitMQ docs and the EAP RabbitMQ in
Action book.  And I'm in the process of evaluating AMQP and Rabbit
specifically for use in a major project.

I generally like what I see in Rabbit, but in the course of my
research, I have run across some statements about it that I would like
to understand better.  For example, this blog post

http://bhavin.directi.com/rabbitmq-vs-apache-activemq-vs-apache-qpid/

makes the following assertions about Rabbit:

1) No ONCE-ONLY semantics. Messages may be sent twice by RabbitMQ to
the consumer(s)

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.