[zeromq-dev] Need for Late join and End of source detection

RohanB rohanb at cs.uchicago.edu
Mon Oct 1 21:13:29 CEST 2012

Hi All,

I'm trying to use ZeroMQ with OpenPGM. Coming from a proprietary messaging 
solution I've been spoiled with two very important features they provided - EOS 
(end of source) and Late Join Cache. Let me explain them here.

1) Late Join Cache:

In a reliable multicast pub-sub environment, late join caches allows subscribers 
that join much late to receive the last published update on that topic. Let me 
explain further. Lets say a publisher is publishing non-frequently changing 
state. If such updates are very infrequently published, subscribers that join 
late may have to wait a while to get the next update. In this situation, late 
join cache on the publisher side allows the publisher to automatically publish 
the last known update on that topic when it detects that a subscriber has just 
joined. This ensures that all subscribers get at-least one last known update, if 
it was ever published, no matter how long ago.

2) EOS:

End of source quite simply generates an asynchronous event on the subscriber 
side when the last publisher on that topic has gone down. This is made possible 
by a heartbeat that goes on under the covers between each subscriber with the 
publisher once connected.

I was wondering if there is support for these features in ZeroMQ. If not are 
there any plans to include the same in upcoming versions? Wondering if anyone 
has other solutions to these problems.

Much appreciated,

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