[zeromq-dev] Why 0mq doesn't define TTL for message (for in-mem queue)?

[Matt Connolly]

If the Tomcat service (layer 1) sends messages asynchronously to the betting service (layer 2), then how is it possible to timeout the response back to the iOS/Android app (layer 0)?

-Matt

On 29 Dec 2013, at 8:13 pm, artemv zmq <artemv.zmq at gmail.com> wrote:

> hi Pieter,
> 
> > You're still not explaining what problem this solves
> 
> Ok. Here's the problem which I faced recently. Here's appl. architecture (to keep discussion focused):
> 
> iOS/Android (game ui)  <----ssl----> Tomcat <-------->  bet_service  .
> 
> There are three layers (from left to right):  game UI (0),  java webserver (1) and concrete service layer (2).  
> Layer#0:
>   - doesn't host 0mq library.
>   - talks to L1 via ssl.
>   - blocking(with timeout) on every call to L1.
> Layer#1:
>   - does host 0mq library.
>   - it's a gateway for game ui. It's an async layer between ui and world of services.
>   - it's _asynchronous_. It's a sort of "delegator/router/etc" for a call from L0  to  L2.
>   - on every call from L0 this layer doesn't wait for response from L2. 
> Layer#2:
>   - does host 0mq library.
>   -  a concrete business service layer.
>   - L0 and L1 _don't care_ will this layer produce response or not.  If not -- L0 will hit call-timeout, L1 -- simply don't care et al.
>  
> The problem is.
> When L2 goes down (whatever reason), then L1 will queue messages, and, by turn, L0 will hit call-timeout. After certain amount of time (usually up to 1hr) L2 will be restarted. And messages,
> which have been queued on L1, will be flying to L2.  In my case, I don't want getting those messages on L2, because they are "out-of-date" for bet_service.  
> 
> The solution is -- TTL for a message.
> I can implement TTL myself, making it being as a part of message, _but_  I don't want to do that, because, TTL is low level thing, so fixing it at higher level would bring more problems, I suppose. 
> 
> 
> 
> 
> 
> 
> 2013/12/29 Pieter Hintjens <ph at imatix.com>
> On Sat, Dec 28, 2013 at 9:52 PM, artemv zmq <artemv.zmq at gmail.com> wrote:
> > That's what I'm talking about ). Why this can't/shouldn't  be done on 0mq?
> > The thing is -- 0mq is queueing solution (after all) and TTL is part of any
> > queueing. TTL is not concrete business feature, it's very common and
> > ubiquitous thing.
> 
> You're still not explaining what problem this solves. Most "queuing
> solutions" offer priorities, acks, persistence, two-phase commits,
> etc. ZeroMQ does not.
> 
> If you want to contribute to ZeroMQ, I'd advise you to use ZeroMQ to
> do do real work, then find areas where you need to make improvements,
> then make those improvements carefully and minimally.
> 
> -Pieter
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