[zeromq-dev] publish/subscribe and the "fast producer" problem

Max Kozlovsky max at portworx.com
Thu Mar 9 20:22:51 CET 2017


Yes you are right, zmq PUSH/PULL model does something different.

In the solution I've outlined there probably be a ROUTER socket in the
producer and consumers will open DEALER sockets to connect to producer and
send requests for more events.

Max

On Thu, Mar 9, 2017 at 10:48 AM, Francesco <francesco.montorsi at gmail.com>
wrote:

> Hi Max,
> thanks for your reply. Just a question:
>
> 2017-03-09 16:35 GMT+01:00 Max Kozlovsky <max at portworx.com>:
> > It seems a pull model might be better in this case.
>
> from my understanding, mostly based on reading zeroMQ - the guide
> (http://zguide.zeromq.org/page:all), the PUSH/PULL model is for
> load-balancing, so that if I change my SUBscribers to be PULLers, and
> my PUBlisher to be a PUSHer, the messages sent by the pusher will be
> load-balanced over the pullers... that is each puller will get a
> different message... I need (possibly) that all pullers get the same
> message...
>
> did I get it right?
>
> Thanks,
> Francesco
>
>
> >Maintain a queue of
> > generated events in the producer of arbitrary finite size with a sequence
> > number. Have consumers pull the events from producer starting from the
> last
> > sequence number they seen. If the queue becomes full, drop the oldest
> event.
> > This gives the best chance for maximum number of consumers to process the
> > events at their own speed.
> >
> > Max
> >
> > On Thu, Mar 9, 2017 at 5:56 AM, Francesco <francesco.montorsi at gmail.com>
> > wrote:
> >>
> >> Hi Max,
> >>
> >> 2017-03-07 20:51 GMT+01:00 Max Kozlovsky <max at portworx.com>:
> >> > I wonder what is the practical application of this model? If for
> >> > correctness
> >> > of the application it is enough to deliver every message to at least
> one
> >> > of
> >> > the subscribers, why not always sent just one copy of a message to
> just
> >> > one
> >> > of the subscribers?
> >> No the correctness model is the following: assume that you have 10
> >> subscribers. Suddenly 1 of them looses connectivity / crashes /
> >> whatever. The other 9 are ok.
> >> What happens is that:
> >> a) If I use the NODROP=1, my publisher blocks and stops processing its
> >> own data, eventually leading to a drop of its own inputs. The whole
> >> system is now blocked (publisher dropping its input events [not coming
> >> from network], 9 subscribers all waiting for the publisher to
> >> publish).
> >> b) If I use a currently non-existing ZMQ_XPUB_ATLEASTONE=1 option, my
> >> publisher keeps publishing, 9 subscribers keep working, just 1 is
> >> stopped / out of service. Outcome in my case: 90% of my application is
> >> still working, I have 10% of data that is not processed and lost.
> >>
> >> Which scenario is best? IMO it's b) :)
> >>
> >>
> >> >Sends to the rest of the subscribers are overhead since
> >> > they are not required for correctness?
> >> They are required, but in case something goes bad I prefer the failure
> >> of a part rather than the failure of everything.
> >>
> >> Francesco
> >> _______________________________________________
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> >> zeromq-dev at lists.zeromq.org
> >> https://lists.zeromq.org/mailman/listinfo/zeromq-dev
> >
> >
> >
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