Re: [wsn] Issue: define queue in WSN

[Anish Karmarkar <Anish.Karmarkar@oracle.com>]

David A. Chappell wrote:

> Agreed.  Here are some things that Sonic has been thinking about 
> regarding the semantics of queuing -
>  
> 1) When a subscriber subscribes, should  it expect to receive messages 
> that were published before the subscription took place?  If queuing 
> semantics were being used underneath the subscription model, then there 
> could be messages queued up that are waiting to be consumed (waiting for 
> hours, days, weeks).
>  
> 2) In JMS there is a notion of a durable subscription, where a 
> subscriber can go offline and have messages queued for it on its behalf 
> while it is unavailable.  Should  we have something comparable in WS-N?
>  
> 3) exactly-once delivery is a generally accepted trait of queues.  A 
> common implementation pattern is load-balanced queue receivers, where 
> multiple receivers listen on the same queue, yet only one of them will 
> receive each individual message.  If I were to overlay WS-N pub/sub 
> topics onto queues in this situation, that would imply a consumption 
> pattern where multiple consumers can subscribe to a given 'Topic', yet 
> only one would recieve each message.
>  
> 3a) That being said: Even in the current draft spec we don't explicity 
> say that in the pub/sub model, all active subscribers are expected to 
> receive a copy of the same message. 

I think this is a good point regardless of whether we support queues or 
not. We need to say exactly what the model is.

> Dave
> 
>     ------------------------------------------------------------------------
>     *From:* Lily Liu [mailto:lily.liu@webmethods.com]
>     *Sent:* Thursday, July 29, 2004 8:05 AM
>     *To:* wsn@lists.oasis-open.org
>     *Subject:* [wsn] Issue: define queue in WSN
> 
>     WSN should address basic messaging queuing concepts.
>      
>     Lily