[zeromq-dev] exiting without missing messages

Mathijs Kwik bluescreen303 at gmail.com
Sat Aug 20 17:57:03 CEST 2011



On 20 aug, 17:11, Pieter Hintjens <p... at imatix.com> wrote:
> On Sat, Aug 20, 2011 at 8:29 AM, Mathijs Kwik <bluescreen... at gmail.com> wrote:
> > So I would rather keep the system simple. I don't mind adding extra
> > sockets so parts can signal each other about adds/removals, but as far
> > as I can tell, zeromq doesn't provide means to do this (disconnect /
> > remove 1 peer from load-balancer).
>
> This is actually the basis for the REQ/REP reliability as well. Look
> at the LRU queue pattern to start with. Now, you can use a
> ROUTER-to-DEALER model, with several alternative ways to know when a
> worker is present or absent:
>
> - heartbeating
> - credit based flow control (seehttp://unprotocols.org/blog:15)
> - synchronous stepping (LRU)
>
> You could also have explicit "bye bye" messages from workers to the
> ventillator but that fails to handle the case where a worker actually
> crashes.
>
> -Pieter

I fail to see how to implement these explicit "bye bye" messages.
I can get a worker to send such a message to the ventilator, I just
don't have a clue on what the ventilator should do when it receives a
byebye.

The case where a worker actually crashes doesn't need to get handled
by the system itself. A worker (or any other component) crashing
should result in the entire system going down (not trying to repair
itself). After a special cleanup/consistency check routine, everything
can be restarted.

Thanks,
Mathijs


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