[zeromq-dev] Check if message is dropped due to HWM at send in ZeroMQ PUB-SUB pattern

[Doron Somech]

So in that case what you want is Majordomo pattern or Freelance pattern if
you don't want a broker.

I don't think pubsub is the correct pattern here.

On Thu, Oct 2, 2014 at 6:23 AM, Ranganath Gunawardane <ranganath at outlook.com
> wrote:

> > Dealer-router doesn't mean request-reply, you can still use one way
> communication.
> Hmm. I will again have to look at the manual.
>
> > Does the message go to one recipient or more?
> A given message is only for a single recipient. Right now in pub-sub it is
> handled by adding
> a unique subscription per recipient.
>
> ------------------------------
> Date: Wed, 1 Oct 2014 13:59:44 +0300
> From: somdoron at gmail.com
>
> To: zeromq-dev at lists.zeromq.org
> Subject: Re: [zeromq-dev] Check if message is dropped due to HWM at send
> in ZeroMQ PUB-SUB pattern
>
> Dealer-router doesn't mean request-reply, you can still use one way
> communication.
>
> You do have to write more logic in the router to route the messages but it
> should be pretty simple logic.
>
> Your protocol between the router and the dealer should include
> registration for tags.
>
> I think you want something that is very similar to Majordomo (
> http://rfc.zeromq.org/spec:7).
>
> Does the message go to one recipient or more?
>
> On Tue, Sep 30, 2014 at 2:32 PM, Ranganath Gunawardane <
> ranganath at outlook.com> wrote:
>
> > Then do not use pub-sub but router-dealer.
> Well, my user case leans more towards a pub-sub pattern than req-reply.
> Let me explain.
>
> I am implementing a messaging service (a message bus) for multiple client
> processes to talk to each other. Every process sends messages with a
> particular 'to' tag. Also, every process subscribes to a unique tag to
> receive messages. This messaging service does not have a sense about the
> content of the message to implement a req-reply mechanism; that is upto the
> clients to handle at a 'business' level.
>
> Sending process do not need to worry about the receive getting it. But I
> at least need to tell the sending client whether they were successful in
> submitting the message to the messaging layer (without hitting send HWM
> etc.).
>
> Because req-reply is out of question (a slow receiver cannot bog down the
> sender), the pub-sub seemed a better approximation.
>
>
> > From: ph at imatix.com
> > Date: Tue, 30 Sep 2014 08:41:56 +0200
> > To: zeromq-dev at lists.zeromq.org
> > Subject: Re: [zeromq-dev] Check if message is dropped due to HWM at send
> in ZeroMQ PUB-SUB pattern
>
> >
> > > I want to let my publisher know if he is dropping messages because he
> has hit the HWM.
> >
> > Then do not use pub-sub but router-dealer. Pub-sub is designed for
> > high volumes with many subscribers. There is no useful way to deal, in
> > the publisher, with a single slow or blocked subscriber, and ZeroMQ
> > pub-sub does not support that.
> >
> > On Tue, Sep 30, 2014 at 1:36 AM, Ranganath Gunawardane
> > <ranganath at outlook.com> wrote:
> > > Hi All, I have implemented a message router using zmq, czmq with
> pub-sub
> > > pattern.
> > >
> > > In my simple test set up, I am using a publisher-subscriber with a
> proxy. I
> > > have a fast sender and a very slow receiver causing messages to hit
> HWM and
> > > drop on send. My exception is that send would fail with 'message
> dropped'
> > > error, but it is not the case. the zmq_msg_send() is not giving me any
> error
> > > even though the messages get dropped (I can verify this by seeing gaps
> in
> > > messages in subscriber end).
> > >
> > > I have looked into fixing slow subscriber problem by adding a sequence
> > > number as you suggested, specially suicidal snail pattern in the
> guide. But
> > > my use case is a bit different. I really do not care about the
> subscribers;
> > > I want to let my publisher know if he is dropping messages because he
> has
> > > hit the HWM.
> > >
> > > I gather that this is the nature of pub-sub. At the same time, from
> > > documentation, it says, if I use ZMQ_DONTWAIT, and 'if the message
> cannot be
> > > queued on the socket, function call shall fail'. Does it mean that I
> can use
> > > this failure as a 'send failure due to buffer full'?
> > >
> > > Regards.
> > > Ranganath
> > >
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