[zeromq-dev] Notes from a hackathon

Thomas Rodgers rodgert at twrodgers.com
Tue Feb 3 23:27:10 CET 2015


>
> * Sessions require protocol commands that are invisible to "normal"
> use. That means either protocol support (e.g. command frames) or some
> layering on top of ZeroMQ blobs.


What would the argument be for not just using command frames for this?

On Tue, Feb 3, 2015 at 4:04 PM, Pieter Hintjens <ph at imatix.com> wrote:

> Thanks for the questions. I'd try to flatter by saying how great these
> questions are, except I know you're all way too smart to fall for
> that. :)
>
> Let me answer a bunch of questions in one go:
>
> * Sorry for not posting this here. I've written a more detailed
> analysis of the motivation for this thread (and experiments):
> http://hintjens.com/blog:84.
>
> * The main goal with this is simplicity and accuracy. I'm tired of
> teaching people ZeroMQ constructs that are clearly over-designed and
> disconnected from reality in subtle ways. Each apology for friction
> ("sorry, but don't use REQ-REP, they are kind of weird", "sorry,
> IDENTITY is not really identity", "sorry, message sometimes means
> frame and sometimes message") really signals costs up and down the
> stacks.
>
> * Sessions require protocol commands that are invisible to "normal"
> use. That means either protocol support (e.g. command frames) or some
> layering on top of ZeroMQ blobs.
>
> * Picture sending solves a cross-language problem, namely how to
> construct zproto-style commands without using dedicated codecs. While
> the API is C-ish, the functionality is not. I'd expect that to be
> wrapped in bindings.
>
> * Per-language serialization is an anti-pattern. It's common, and fine
> as such, yet ZeroMQ should IMO always strive to be cross-language.
>
> * REQ-REP between threads may make sense. We certainly use it (ZAP,
> for authentication).
>
> * Is this discussion C4 compatible? Yes, no, this is chatter, not a
> plan or roadmap. Until pull requests hit the road, it's all vapour.
> However the problems I restated in my blog article are real, to many
> people, and should be aired.
>
> * Multipart does easy serialization, yes. Not in C though. We've
> learned how to do variable list serialization with zproto-compatible
> picture sending in CZMQ. Is this a sufficient alternative? I think so.
> zsock_send() was essential to making actors cheap enough to use
> widely. egrep zsock_send *.c in malamute-core/src.
>
> * Locking on socketsL: we did in fact have a pull request for this
> once. It was... nasty. We reverted it. We breathed a sigh of relief.
> However looking back, the problem was valid and has never been solved
> since.
>
> * If you're doing multipart a lot in an application, you can replace
> that with zproto. You already have contracts then, why not make them
> explicit and documented? That's always a win in my experience.
>
> * Multi-hop request reply is a strange beast and I'm keen to
> understand those architectures that use it. My suspicion is that we've
> shifted our vision of what ZeroMQ "is" over the years. My own
> experience seems plausible, yet I distrust it. So, the stories in my
> article are please for falsification, not attempts to convince.
>
> * I think we have learned to not break existing code. It's going to be
> interesting to run multiple models at once. We do this in CZMQ and it
> works OK. There isn't much overhead.
>
> * Authentication and routing information should be (MUST be) two
> totally separate layers. CURVE certainly does not use the routing ID
> (even if it's still misnamed as "IDENTITY"). You can have the same
> client on N connections (obviously). You authenticate a client using a
> mechanism-specific key: PLAIN user id, or CURVE public key.
>
> -Pieter
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