[zeromq-dev] v3.1 publisher filtering

Steve steve.friendly at gmail.com
Wed Mar 14 00:22:44 CET 2012


I setup the "C++ weather update" client / server (from the ZeroMQ guide) on
two machines.  I have the server on one machine and the client on another.
I hard coded the server to only publish zip code "11111".  The client
subscribes to "22222".  Although my client code doesn't 'see' the messages
(as expected), I see the "11111" messages traveling to the client machine
using WireShark so ZeroMQ must be filtering them out on the client side
(not the publishing side).

I was interested in the built-in PubSub as a possible foundation to build a
game server with 100's or 1000's of clients (players).  However, if each
published messages has to go to each client (even if they don't need it) I
think it will overwhelm the network (or the clients machine).  This would
be especially true for slower clients like mobile devices.  The v3.1 XPUB
XSUB only solves part of the problem if you are using many layers of
publishers and subscribers.  However, I haven't found a pattern or solution
where someone has dealt with the "last published leg" where the messages
are sent to the client end points.  Maybe the "Dealer" / "Router" would
work but it sounded like there might be some problems if the clients
disconnected.

Any other thoughts are appreciated.

Thanks,

Steve



On Tue, Mar 13, 2012 at 12:39 PM, Calvin de Vries
<devries.calvin at gmail.com>wrote:

> I'm not sure this is correct, Joshua. PUB filters the messages in 3.1,
> while you can use XPUB in order to do more advanced subscription
> management, it is not a requirement to have publisher side filtering.
>
> In Steve's example, Subscriber A would not receive every message, only
> messages matching its filter.
>
>
> On Mon, Mar 12, 2012 at 7:43 PM, Joshua Foster <jhawk28 at gmail.com> wrote:
>
>>  3.1 works the same way as 2.1 in your example. The changes in 3.1 is
>> that the subscription is forwarded to the PUB socket. This allows you to
>> create a publisher device. It would sit between the parent publisher and
>> the subscriber. The XPUB keeps track of the subscriptions and allows them
>> to apply to the XSUB socket. This effectively filters out any messages that
>> do not match a subscription. In your example, you are matching against "a"
>> and "" so all messages would be passed through.
>>
>> You can of course use a ROUTER socket and manage the subscriptions
>> yourself in the application (with DEALER). The main downside is that you
>> won't be able to detect client disconnections. You may also want to
>> consider creating an alternative PUB socket implementation in ZeroMQ.
>>
>> Joshua
>>
>>
>> On 3/12/2012 6:48 PM, Steve wrote:
>>
>> I have a high level question about how a v3.1 publisher handles sending
>> updates to subscribers.  I understand that v3.1 can push the subscription
>> filtering further towards the publisher but to what degree I'm unclear on.
>>
>> Here is a very simple usage example:
>>
>> 1) Publisher has a list of topics that are randomly updated 10 times a
>> second.  There are a total of 26 topics and each is a single lowercase
>> alpha character representing the English alphabet (a - z).
>> 2) Subscriber 'A' subscribes to just a topic matching "a".
>> 3) Subscriber 'B' subscribes to all topics ("").
>>
>> In version 2.1, I believe Subscriber 'A' would receive all the messages
>> and that the zeromq client library would filter them so the client would
>> only see updates on 'a'.  In version 3.1, is it possible to filter the
>> messages at the publisher so that Subscriber 'A' only receives updates on
>> topic 'a' (no filtering done on the client) and that Subscriber 'B'
>> receives all updates on all topics (a-z)?
>>
>> Thanks,
>>
>> Steve
>>
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