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Multiple consumption of queued messages Disclosure Number: IPCOM000125711D
Original Publication Date: 2005-Jun-14
Included in the Prior Art Database: 2005-Jun-14
Document File: 1 page(s) / 36K

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We outline a mapping of the Publish/Subscribe messaging paradigm into the Point-to-Point messaging paradigm, enabling Pub/Sub implementations using Point-to-Point features. We describe problems with existing such implementations, and extend the Point-to-Point paradigm to achieve a simplified and better performing mapping than those presently available.

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Multiple consumption of queued messages

A common messaging paradigm is Publish/Subscribe; a message is published to a named topic and is then consumed by multiple subscribers. Another common messaging paradigm is Point-to-Point; a message is put to a named queue and is consumed by a single receiver.

    Common implementations of the publish/subscribe paradigm are typically built upon the point-to-point paradigm. This is achieved through the use of a broker application, which maintains a list of subscribers for each topic and performs fan-out of published messages. For each subscriber to a topic, the broker sends a copy of the message to a queue chosen by the subscriber.

    This solution has a number of problems; the number of fanned-out messages increases linearly with the number of subscribers and hence the storage required increases in the same fashion. Similarly, the time taken to publish a message also increases with the number of subscribers. Additionally, subscribers need to deregister and explicitly remove any of their message copies on the queue when they are finished - and a common form of Publish/Subscribe requires the subscriber to deregister on crash. This requires some failure detection and cleanup step in addition to that normally provided by the Point-to-Point solution. Also, to make the fanned-out message copies sit neatly in the Point-to-Point framework, the broker may need to alter the message as it gets fanned-out; for example to give each copy a unique message id. Finally, the broker introduces a time-delay between the publish operation and the availability of the message; so if a publisher and a subscriber share a thread, a pu...