[zeromq-dev] Fundamental question on ZMQ. How to determine message fail/success without HWM-arking?

Fri Dec 6 19:57:45 CET 2013

The actual semantics vary according to sock type and are specified in
various RFCs: 28, 29, 30, 31 (rfc.zeromq.org).

On Fri, Dec 6, 2013 at 5:15 PM, artemv zmq <artemv.zmq at gmail.com> wrote:
> Thanks Justin.
>
> But still following points remain unanswered:
> - why socket.send() returns "true"  when sending to unexisting peer
> (socket.hwm=0) ?
> - why poller.pollout()  returns "true"  (socket registered on POLLOUT) when
> polling socket which is connected  to unexisting peer ?
>
> For the first case: either prohibit 0 as an argument value or please bring a
> light on expected behaviour. For second -- such "polling" looks strange,
> isn't?
>
>
> BR
> -artemv
>
>
>
>
> 2013/12/6 Justin Cook <jhcook at gmail.com>
>>
>> Artem,
>>
>> The “high-water mark” is simply used to prevent memory exhaustion:
>>
>> "It has ways of dealing with over-full queues (called "high water mark").
>> When a queue is full, ØMQ automatically blocks senders, or throws away
>> messages, depending on the kind of messaging you are doing (the so-called
>> "pattern”).”
>>
>> It has nothing to do with with specific peers.  What you are doing is
>> setting the HWM to a low number and then hoping for a send() to block — not
>> return false — if the queue is exhausted. You then assume that a peer is
>> down if you were to block. Given that the behaviour differs based on the
>> messaging pattern you are using, you will need to setup a test case.
>>
>> If I were you, I would abandon this idea and investigate what Pieter said
>> @1311. Sequence numbering and NACKs is what I would look at.
>>
>> Once you have done that, feel free to generate a test case and share with
>> us on the list.
>>
>> --
>> Justin Cook
>>
>>
>> On Friday, 6 December 2013 at 13:59, artemv zmq wrote:
>>
>> > Thanks Pieter. All this sounds new to me ... :|
>> >
>> > But if we return to HWM question -- when I set hwm=0 and sending to
>> > unexistent peer, then every .send() call return me "true". Is not this an
>> > issue in ZMQ core?
>> >
>> >
>> > BR
>> > -artemv
>> >
>> >
>> >
>> > 2013/12/6 Pieter Hintjens <ph at imatix.com (mailto:ph at imatix.com)>
>> > > You should probably think about a mix of sequence numbering, credit
>> > > based flow control and negative acks that flow asynchronously against
>> > > the message flow. You can then send without waiting, ensure you never
>> > > overrun buffers, and catch errors if they happen.
>> > >
>> > > On Fri, Dec 6, 2013 at 2:02 PM, artemv zmq <artemv.zmq at gmail.com
>> > > (mailto:artemv.zmq at gmail.com)> wrote:
>> > > > 2Matt:
>> > > >
>> > > > > > Sending a message may take some time (connection latency, etc)
>> > > > > > so how
>> > > > > > long do you think it will take to send the message before you
>> > > > > > assume it has
>> > > > > > been sent or not?
>> > > > >
>> > > >
>> > > > Sure thing -- I can go with some reasonable timeout specified via
>> > > > properties/cmdline. Not a problem.
>> > > >
>> > > > > > If you want send() to return false
>> > > > The only way I found ZMQ can give me false on .send() -- is to set
>> > > > hwm=1
>> > > > and send two messages everytime:
>> > > >
>> > > > --send_dummy_scout_msg-->
>> > > > --send_bet_msg-->
>> > > > --send_dummy_scout_msg-->
>> > > > -- X
>> > > >
>> > > > Got idea? If "dummy_scout" stucked in a queue, then "bet_msg" will
>> > > > not be
>> > > > sent , so .send() will return me "false". Pretty stupid... Not sure
>> > > > I can
>> > > > seriously explain this to chief architects :) Is there other way?
>> > > >
>> > > >
>> > > >
>> > > > 2013/12/6 Diego Duclos <diego.duclos at palmstonegames.com
>> > > > (mailto:diego.duclos at palmstonegames.com)>
>> > > > >
>> > > > > If ALL you need is to know is "has message left NIC on sending
>> > > > > process or
>> > > > > not", there is a socket option for that. It's called
>> > > > > ZMQ_ROUTER_MANDATORY.
>> > > > >
>> > > > >
>> > > > > On Fri, Dec 6, 2013 at 1:07 PM, Matt Connolly
>> > > > > <matt.connolly at me.com (mailto:matt.connolly at me.com)>
>> > > > > wrote:
>> > > > > >
>> > > > > > Could you use the socket monitoring to check the connected state
>> > > > > > of the
>> > > > > > dealer socket?
>> > > > > >
>> > > > > > Sending a message may take some time (connection latency, etc)
>> > > > > > so how
>> > > > > > long do you think it will take to send the message before you
>> > > > > > assume it has
>> > > > > > been sent or not?
>> > > > > >
>> > > > > > If you want send() to return false, you would need it to be a
>> > > > > > blocking
>> > > > > > synchronous call which against the idea of queuing messages to
>> > > > > > be sent (as
>> > > > > > far as I understand)
>> > > > > >
>> > > > > > Good luck
>> > > > > >
>> > > > > > Cheers,
>> > > > > > Matt.
>> > > > > >
>> > > > > > On 6 Dec 2013, at 9:19 pm, artemv zmq <artemv.zmq at gmail.com
>> > > > > > (mailto:artemv.zmq at gmail.com)> wrote:
>> > > > > >
>> > > > > > Sorry for confusion.
>> > > > > >
>> > > > > > When I said out-of-control -- I meant they do have ZMQ but they
>> > > > > > may have
>> > > > > > different release cycle and QoS. It's just a service on ZMQ, on
>> > > > > > a ROUTER.
>> > > > > >
>> > > > > > Our application is aimed to take a message, get its headers,
>> > > > > > decide on
>> > > > > > what service ROUTER to send and that's it. W/o waiting for
>> > > > > > reply.
>> > > > > > Essentially we are a DEALER.
>> > > > > > Replies are important, but as long as they coming back. If they
>> > > > > > not. Not
>> > > > > > a problem. Client application (iPhone game) by itself checking
>> > > > > > replies and
>> > > > > > correlation,
>> > > > > > and keep watching: "ahha, I didn't receive ack for betting.
>> > > > > > hmmm. Let's
>> > > > > > try again". Now it's more clear?
>> > > > > >
>> > > > > > I really don't need PUB/SUB. I need DEALER/ROUTER. Here, in my
>> > > > > > company,
>> > > > > > the only biggest concern so far with ZMQ -- misleading
>> > > > > > behaviour:
>> > > > > > when .send() returns "true" that should mean that message
>> > > > > > "sent",
>> > > > > > whatever that means: left our PID, left our NIC and so on, we
>> > > > > > have to
>> > > > > > guarantee that message is not on us.
>> > > > > > I know what's PUB/SUB. And again, telling you that it's not
>> > > > > > suitable. The
>> > > > > > problem statement is simple:
>> > > > > >
>> > > > > > - don't use HWM for DEALER/ROUTER (prohibit message queueing).
>> > > > > > - raise immediately if you can't .send() (don't collect in
>> > > > > > internal
>> > > > > > queue)
>> > > > > >
>> > > > > >
>> > > > > > Is it possible?
>> > > > > >
>> > > > > >
>> > > > > > BR
>> > > > > > -artemv
>> > > > > >
>> > > > > >
>> > > > > > 2013/12/6 Justin Cook <jhcook at gmail.com
>> > > > > > (mailto:jhcook at gmail.com)>
>> > > > > > >
>> > > > > > > Ok, this is confusing. If you are sending a message to a
>> > > > > > > service that is
>> > > > > > > out of your control, either they use 0MQ or not. I assume they
>> > > > > > > do not. If
>> > > > > > > that’s the case, it should not be a part of the use case.
>> > > > > > >
>> > > > > > > You say you need to know if a message has been received. But,
>> > > > > > > then you
>> > > > > > > say no ACKs or timeouts. I’m even more confused. If you are
>> > > > > > > making a request
>> > > > > > > to a foreign service over — I assume — HTTP which uses TCP,
>> > > > > > > you are very
>> > > > > > > well getting HTTP return codes with the TCP session doing all
>> > > > > > > the hard work.
>> > > > > > > You already have what you are looking for there.
>> > > > > > >
>> > > > > > > As far as your system — going out to mobile devices — using
>> > > > > > > PUB/SUB and
>> > > > > > > ACKing messages, this is something you will have to do in
>> > > > > > > another channel
>> > > > > > > with 0MQ. Multicast uses UDP; because, it is not feasible to
>> > > > > > > send TCP ACKs
>> > > > > > > from every single subscriber. It’s simply not scalable.
>> > > > > > >
>> > > > > > > You very well may need to develop your own application
>> > > > > > > protocol to send
>> > > > > > > ACKs or the publisher retransmits. I highly suggest you have a
>> > > > > > > look at this:
>> > > > > > >
>> > > > > > >
>> > > > > > >
>> > > > > > > http://stackoverflow.com/questions/12956685/what-are-the-retransmission-rules-for-tcp
>> > > > > > >
>> > > > > > > It may be something you will want to mimic in your
>> > > > > > > implementation.
>> > > > > > > Someone else has already suggested a timeout for resending
>> > > > > > > unacknowledged
>> > > > > > > messages. As you can see, this is one of the ways TCP
>> > > > > > > retransmissions work.
>> > > > > > > You also may have corrupt data that fail a CRC or hash.
>> > > > > > >
>> > > > > > > I will finish by saying that if you do have a PUB/SUB design
>> > > > > > > using
>> > > > > > > another channel for unicast communication, you will need to be
>> > > > > > > very aware of
>> > > > > > > scalability issues. You may need to use a lockstep pattern
>> > > > > > > such as REQ/REP
>> > > > > > > if you need guarantee of communication.
>> > > > > > >
>> > > > > > > --
>> > > > > > > Justin Cook
>> > > > > > >
>> > > > > > >
>> > > > > > > On Friday, 6 December 2013 at 09:46, artemv zmq wrote:
>> > > > > > >
>> > > > > > > > Thanks for heads up.
>> > > > > > > >
>> > > > > > > > 2crocket:
>> > > > > > > > No acks. No timeouts. Nothing should be kept. Messages
>> > > > > > > > should just
>> > > > > > > > flowing back and forth. But for every message we have to
>> > > > > > > > answer a question:
>> > > > > > > > "has message left NIC on sending process or not". Let me
>> > > > > > > > give example with
>> > > > > > > > betting: game on iPhone sending us a message "make-a-bet",
>> > > > > > > > then we send this
>> > > > > > > > to BettingService which isn't in our control,
>> > > > > > > > so all we have to guarantee -- "make-a-bet" message has left
>> > > > > > > > our NIC
>> > > > > > > > and been "sent" to BettingService. If "make-a-bet" has been
>> > > > > > > > droped on a
>> > > > > > > > network - ok, if BettingService itself drops it - ok.
>> > > > > > > >
>> > > > > > > > Back to HWM. Let's consider that we send to unavaliable
>> > > > > > > > peer.
>> > > > > > > > hwm=1. It means you can send 1 message "blindly" and .send()
>> > > > > > > > function
>> > > > > > > > returns success. Of course sending second time will fail.
>> > > > > > > > But... the trick
>> > > > > > > > is -- we need answer first time.
>> > > > > > > > hwm=0. It means you can send any number of messages and
>> > > > > > > > .send()
>> > > > > > > > function _always_ returns success :(( Again, isn't this a
>> > > > > > > > bug?
>> > > > > > > >
>> > > > > > > >
>> > > > > > > > So let me re-phrase the original question -- how to fail at
>> > > > > > > > .send()
>> > > > > > > > function in ZMQ?
>> > > > > > > >
>> > > > > > > >
>> > > > > > > > BR
>> > > > > > > > -artemv
>> > > > > > > >
>> > > > > > > >
>> > > > > > > >
>> > > > > > > > 2013/12/6 crocket <crockabiscuit at gmail.com
>> > > > > > > > (mailto:crockabiscuit at gmail.com)
>> > > > > > > > (mailto:crockabiscuit at gmail.com)>
>> > > > > > > > > Why don't you set a timeout for asynchronous ACKs?
>> > > > > > > > > You receive ACKs asynchronously and keep associated
>> > > > > > > > > messages until
>> > > > > > > > > ACKs come or a timeout occurs.
>> > > > > > > > > A timeout of 20 seconds is a reasonable estimate.
>> > > > > > > > > After a timeout, if a message doesn't have a corresponding
>> > > > > > > > > ACK, it
>> > > > > > > > > is determined that the message wasn't delievered, and the
>> > > > > > > > > message is sent
>> > > > > > > > > again or discarded.
>> > > > > > > > >
>> > > > > > > > >
>> > > > > > > > >
>> > > > > > > > > On Fri, Dec 6, 2013 at 3:19 AM, artemv zmq
>> > > > > > > > > <artemv.zmq at gmail.com (mailto:artemv.zmq at gmail.com)
>> > > > > > > > > (mailto:artemv.zmq at gmail.com)> wrote:
>> > > > > > > > > > Hi,
>> > > > > > > > > >
>> > > > > > > > > > My name is Artem. I stay with ZMQ (on java) a year or
>> > > > > > > > > > so. Got a
>> > > > > > > > > > cool question for you, ppl!
>> > > > > > > > > >
>> > > > > > > > > > Here's my story. Recently I entered a new company
>> > > > > > > > > > (gambling
>> > > > > > > > > > games), after working few weeks, after getting
>> > > > > > > > > > accustomed with a code, I
>> > > > > > > > > > found that they are building
>> > > > > > > > > > very-unnecessarly-complex-distibuted-application ... I
>> > > > > > > > > > was unhappy few days,
>> > > > > > > > > > because couldn't even imagine how to support ALL THAT
>> > > > > > > > > > CRAP in an upcoming
>> > > > > > > > > > future. So I suggested ZMQ hoping that ZMQ will "open
>> > > > > > > > > > eyes" to others. But,
>> > > > > > > > > > as a feedback I got one big fundamental concern (from
>> > > > > > > > > > chief architects):
>> > > > > > > > > >
>> > > > > > > > > > - we have to know only one thing about every message: it
>> > > > > > > > > > has been
>> > > > > > > > > > delivered onto remote peer or not
>> > > > > > > > > >
>> > > > > > > > > > And few additional comments:
>> > > > > > > > > > -we don't care if message will get lost on a network
>> > > > > > > > > > - we don't need guarantee deliveri
>> > > > > > > > > > - no RPC / everything is asynchronous
>> > > > > > > > > > - we don't need HWM
>> > > > > > > > > >
>> > > > > > > > > >
>> > > > > > > > > > So I'm here, because I really can't address this
>> > > > > > > > > > question: "for
>> > > > > > > > > > every single message how to know : whether it was
>> > > > > > > > > > delivered or not" .
>> > > > > > > > > >
>> > > > > > > > > > Thanks in advance. And appreciate for your help.
>> > > > > > > > > > _______________________________________________
>> > > > > > > > > > zeromq-dev mailing list
>> > > > > > > > > > zeromq-dev at lists.zeromq.org
>> > > > > > > > > > (mailto:zeromq-dev at lists.zeromq.org) (mailto:zeromq-dev at lists.zeromq.org)
>> > > > > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > > > > > > > >
>> > > > > > > > >
>> > > > > > > > >
>> > > > > > > > >
>> > > > > > > > > _______________________________________________
>> > > > > > > > > zeromq-dev mailing list
>> > > > > > > > > zeromq-dev at lists.zeromq.org
>> > > > > > > > > (mailto:zeromq-dev at lists.zeromq.org) (mailto:zeromq-dev at lists.zeromq.org)
>> > > > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > > > > > > >
>> > > > > > > >
>> > > > > > > >
>> > > > > > > > _______________________________________________
>> > > > > > > > zeromq-dev mailing list
>> > > > > > > > zeromq-dev at lists.zeromq.org
>> > > > > > > > (mailto:zeromq-dev at lists.zeromq.org) (mailto:zeromq-dev at lists.zeromq.org)
>> > > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > > > > > >
>> > > > > > >
>> > > > > > >
>> > > > > > >
>> > > > > > > _______________________________________________
>> > > > > > > zeromq-dev mailing list
>> > > > > > > zeromq-dev at lists.zeromq.org
>> > > > > > > (mailto:zeromq-dev at lists.zeromq.org)
>> > > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > > > > >
>> > > > > >
>> > > > > >
>> > > > > > _______________________________________________
>> > > > > > zeromq-dev mailing list
>> > > > > > zeromq-dev at lists.zeromq.org (mailto:zeromq-dev at lists.zeromq.org)
>> > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > > > > >
>> > > > > >
>> > > > > > _______________________________________________
>> > > > > > zeromq-dev mailing list
>> > > > > > zeromq-dev at lists.zeromq.org (mailto:zeromq-dev at lists.zeromq.org)
>> > > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > > > >
>> > > > >
>> > > > >
>> > > > > _______________________________________________
>> > > > > zeromq-dev mailing list
>> > > > > zeromq-dev at lists.zeromq.org (mailto:zeromq-dev at lists.zeromq.org)
>> > > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > > >
>> > > >
>> > > >
>> > > > _______________________________________________
>> > > > zeromq-dev mailing list
>> > > > zeromq-dev at lists.zeromq.org (mailto:zeromq-dev at lists.zeromq.org)
>> > > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> > >
>> > > _______________________________________________
>> > > zeromq-dev mailing list
>> > > zeromq-dev at lists.zeromq.org (mailto:zeromq-dev at lists.zeromq.org)
>> > > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>> >
>> >
>> > _______________________________________________
>> > zeromq-dev mailing list
>> > zeromq-dev at lists.zeromq.org (mailto:zeromq-dev at lists.zeromq.org)
>> > http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>>
>>
>>
>> _______________________________________________
>> zeromq-dev mailing list
>> zeromq-dev at lists.zeromq.org
>> http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>
>
>
> _______________________________________________
> zeromq-dev mailing list
> zeromq-dev at lists.zeromq.org
> http://lists.zeromq.org/mailman/listinfo/zeromq-dev
>