I've been testing rabbitmq with pika (python) to understand how they
interact and learn about the AMQP protocol. I've some questions and
some complaints; no doubt much of this will be from my
misunderstandings of the AMQP/rabbitmq specs.

Pika (is this better posted to the pika mailing list?):

1. why is the test in channel.py:102 like so:
if callback and not isinstance(callback, types.FunctionType) and \
not isinstance(callback, types.MethodType):
raise TypeError("callback should be None, a function or method.")

i.e. why isn't is just a callable() test e.g.
if callback and not callable(callback):
raise TypeError("callback should be callable.")

(is this a python-3 compatibility thing?)


2. documentation for callback functions is mostly non-existent, and when it
exists is sometimes wrong e.g. on http://pika.github.com/channel.html :

(i) channel.basic_get:
"callback method signature should have 3 parameters:
The method frame, header frame and the body"
In fact the callback gets 4 parameters:
channel, method (Basic.GetOk), properties (Basic.Properties), body

(ii) channel.add_on_close_callback:
"The callback function should receive a frame parameter."
In fact the callback gets 2 parameters: error_code, error_message


3. why does basic_ack cause this warning?
CallbackManager.add: Duplicate callback found for "0:Connection.CloseOk"
i.e. why does it appear to add a(nother) connection close callback?
I've grubbed through the pika source but can't see how/where it happens.


AMQP/rabbitmq:

4. why doesn't basic_ack do what I expect?
If I do a basic_get with no_ack=False, and then a basic_ack,
the message stays on the queue.
I can repeatedly fetch-and-ack it, and each time redelivered=true.


5. if the server reaches a state where it stops accepting messages
(e.g. memory usage exceeds the high water mark) it does not send
nack or return responses to basic_publish.
This is both with transactions, or with channel confirm_delivery
enabled.


(5) is a concern when one requires guaranteed delivery. Having the
server swallow the message and not respond doesn't seem reliable to
me. Is there some other method I should be using for guaranteed
delivery?

Alistair

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postedFeb 29, '12 at 1:54a
activeFeb 29, '12 at 10:28a
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