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

[Ranganath Gunawardane]

> 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 addinga 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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> > zeromq-dev at lists.zeromq.org
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