[zeromq-dev] v3.1 publisher filtering

Joshua Foster jhawk28 at gmail.com
Wed Mar 14 02:30:06 CET 2012


The publisher side filtering implementation is in the m_trie (used by 
XPUB). I missed it the last time I was looking for it. It uses the trie 
data structure to link subscriptions to pipes. You can use XPUB in place 
of PUB. You will just need to throw away the recv's.

Joshua

On 3/13/2012 7:22 PM, Steve wrote:
>
> 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 <mailto: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
>     <mailto: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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