Excerpts from Samuel Merritt's message of 2014-09-09 19:04:58 -0700:
> On 9/9/14, 4:47 PM, Devananda van der Veen wrote:
> > On Tue, Sep 9, 2014 at 4:12 PM, Samuel Merritt <s...@swiftstack.com> wrote:
> >> On 9/9/14, 12:03 PM, Monty Taylor wrote:
> > [snip]
> >>> So which is it? Because it sounds like to me it's a thing that actually
> >>> does NOT need to diverge in technology in any way, but that I've been
> >>> told that it needs to diverge because it's delivering a different set of
> >>> features - and I'm pretty sure if it _is_ the thing that needs to
> >>> diverge in technology because of its feature set, then it's a thing I
> >>> don't think we should be implementing in python in OpenStack because it
> >>> already exists and it's called AMQP.
> >>
> >>
> >> Whether Zaqar is more like AMQP or more like email is a really strange
> >> metric to use for considering its inclusion.
> >>
> >
> > I don't find this strange at all -- I had been judging the technical
> > merits of Zaqar (ex-Marconi) for the last ~18 months based on the
> > understanding that it aimed to provide Queueing-as-a-Service, and
> > found its delivery of that to be lacking on technical grounds. The
> > implementation did not meet my view of what a queue service should
> > provide; it is based on some serious antipatterns (storing a queue in
> > an RDBMS is probably the most obvious); and in fact, it isn't even
> > queue-like in the access patterns enabled by the REST API (random
> > access to a set != a queue). That was the basis for a large part of my
> > objections to the project over time, and a source of frustration for
> > me as the developers justified many of their positions rather than
> > accepted feedback and changed course during the incubation period. The
> > reason for this seems clear now...
> >
> > As was pointed out in the TC meeting today, Zaqar is (was?) actually
> > aiming to provide Messaging-as-a-Service -- not queueing as a service!
> > This is another way of saying "it's more like email and less like
> > AMQP", which means my but-its-not-a-queue objection to the project's
> > graduation is irrelevant, and I need to rethink about all my previous
> > assessments of the project.
> >
> > The questions now before us are:
> > - should OpenStack include, in the integrated release, a
> > messaging-as-a-service component?
> I certainly think so. I've worked on a few reasonable-scale web 
> applications, and they all followed the same pattern: HTTP app servers 
> serving requests quickly, background workers for long-running tasks, and 
> some sort of durable message-broker/queue-server thing for conveying 
> work from the first to the second.
> A quick straw poll of my nearby coworkers shows that every non-trivial 
> web application that they've worked on in the last decade follows the 
> same pattern.
> While not *every* application needs such a thing, web apps are quite 
> common these days, and Zaqar satisfies one of their big requirements. 
> Not only that, it does so in a way that requires much less babysitting 
> than run-your-own-broker does.

I think you missed the distinction.

What you describe is _message queueing_. Not messaging. The difference
being the durability and addressability of each message.

As Devananda pointed out, a queue doesn't allow addressing the items in
the queue directly. You can generally only send, receive, ACK, or NACK.

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