[rabbitmq-discuss] Handling Channel.Flow method
celldee at gmail.com
Wed Jan 6 17:07:29 GMT 2010
On 6 Jan 2010, at 16:50, Gordon Sim wrote:
> On 01/06/2010 06:55 AM, Alexis Richardson wrote:
>> On Wed, Jan 6, 2010 at 4:40 AM, Chris Duncan<celldee at gmail.com>
>>> I've also been reading the AMQP 0-10 specification. I have only
>>> skimmed it
>>> before because I wasn't targeting a broker that implemented it.
>>> It contains
>>> a section about transfer of responsibility that seems to deal
>>> with the
>>> issues that I've been trying to address in my last two posts.
>> Yes, that's how we designed it. But, the goal of 0-10 was to provide
>> a way to use acks and nacks for exactly-once delivery. Your email
>> only asks for an ack. That's a bit easier and IMO better.
> The need for some confirmation of publish is much wider than
> exactly-once delivery. That confirmation mechanism should also
> support asynchronous use if desired to avoid the performance impact
> Scott points out[*].
> The 0-10 protocol doesn't really provide nacks per se. It has a
> message-release command which is useful when subscribers want to
> use prefetch and need to relinquish some of the messages delivered
> to them without killing the session.
> [*] Perhaps of interest to mention that there was some disagreement
> within the amqp wg on whether -ok response to methods identified as
> synchronous by the 0-8 spec could be used asynchronously i.e.
> whether it was valid to send methods without waiting for the -ok
> and process receipt of those -ok response as they arrive in the
> other direction. Most (all?) of them aren't explicitly correlated,
> so were you to do that you would need to rely on the order of -oks
> matching the order of methods which if I recall correctly was the
> cause for concern at the time.
I thought that the :nowait argument in the 0-8, 0-9 and 0-9-1 specs
was what provides the ability to use synchronous methods in an
asynchronous fashion. When I use the terms synchronous and
asynchronous here I'm using them in the manner that the AMQP specs
seem to use them; namely synchronous methods send a response to tell
you whether they've succeeded and asynchronous ones don't. If :nowait
is set to true doesn't that mean that the server will not send an -ok
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