RE: [wsn] Issue: define queue in WSN

["David A. Chappell" <chappell@sonicsoftware.com>]

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. 

Dave

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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