[zeromq-dev] Order by which PUB/SUB requests are sent/processed

Joegen Baclor jbaclor at ezuce.com
Wed Jan 25 03:12:23 CET 2012


I understand that Martin and we do require that all queue participants 
gets the message.   However, there is one unique requirement in our 
application that pops certain data from a common queue as soon as one 
subscriber receives the message.  If there are three subscribers there 
will be 3 pops happening.  Only one would succeed.   The two other which 
fails follows a different logical task.  The fan out strategy for 
pub-sub although virtually happening simultaneously is still single 
threaded and thus would line up in the transport rendering the effect of 
having a strict priority in terms of which subscriber gets the first 
chance to pop the event from the other queue.  What we wanted to achieve 
is that no single subscriber gets the chance.  Thanks in advance for 
your time.

On 01/25/2012 09:52 AM, Martin Sustrik wrote:
> Hi Joegen,
>
> PUB socket sends every message to *every* subscriber. Thus they should 
> arrive at the destinations at approximately the same time.
>
> Exact time of course depends on network latency between publisher and 
> individual subscribers.
>
> Martin
>
> On 01/25/2012 10:41 AM, Joegen Baclor wrote:
>> Just in case someone finds time to look into my issue, I am attaching
>> the publisher code. Perhaps there is something I am doing wrong or
>> options i need to set to achieve a fairly-queued sending of events.
>>
>> On 01/24/2012 06:27 PM, Joegen Baclor wrote:
>>> Hi,
>>>
>>> We have an application the uses PUP/SUB sockets. One requirement that
>>> ZeroMQ gracefully meets is being able to reliably send events to all
>>> subscribers. However, there is a requirement in our application that
>>> relies on which client gets the event first. We were under the
>>> assumption that ZeroMQ randomizes the sending of events to the mutiple
>>> subscribers so that no one subscriber always gets a first hit.
>>> Unfortunately, this seems to be not the case. ZeroMq seems to follow a
>>> specific fix order. We have created 3 clients each incrementing a
>>> counter if it was the first one to get the publication. Take the
>>> output below (each iteration is 1500 events):
>>>
>>> Iteration 0
>>> Client 1 processed 1496 events.
>>> Client 2 processed 0 events.
>>> Client 3 processed 4 events.
>>>
>>> Iteration 1
>>> Client 1 processed 2309 events.
>>> Client 2 processed 647 events.
>>> Client 3 processed 44 events.
>>>
>>> Iteration 2
>>> Client 1 processed 2992 events.
>>> Client 2 processed 1385 events.
>>> Client 3 processed 123 events.
>>>
>>> Iteration 3
>>> Client 1 processed 3623 events.
>>> Client 2 processed 1951 events.
>>> Client 3 processed 426 events.
>>>
>>> Iteration 4
>>> Client 1 processed 4207 events.
>>> Client 2 processed 2697 events.
>>> Client 3 processed 723 events.
>>> TestDriver::TestMultiplePop ... Ok
>>>
>>> Clearly, the order is predictable. client 1 gets the highest hit and
>>> client 3 gets the lowest hit. Is there a way so that we can spread
>>> this evenly across the subscribers?
>>>
>>> Joegen
>>>
>>>
>>>
>>
>>
>>
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>
>




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