Browse Prior Art Database

Management of Retained Messages in Publish/Subscribe System

IP.com Disclosure Number: IPCOM000123668D
Original Publication Date: 1999-Mar-01
Included in the Prior Art Database: 2005-Apr-05
Document File: 1 page(s) / 49K

Publishing Venue

IBM

Related People

Bolam, S: AUTHOR [+5]

Abstract

Message handling systems using the Publish/Subscribe concept sometimes distinguish between event and state messages. An event might describe a trade or a vehicle movement, while a state could describe a price or a temperature. Publishers mark messages representing state as 'retained'. Brokers hold retained publications - one per topic - until replaced by a new publication. A new subscriber to a topic having a retained publication will receive the current one, whereas a new subscriber to a topic carrying event data will receive the next published message.

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Management of Retained Messages in Publish/Subscribe System

   Message handling systems using the Publish/Subscribe
concept sometimes distinguish between event and state messages.  An
event might describe a trade or a vehicle movement, while a state
could describe a price or a temperature.  Publishers mark messages
representing state as 'retained'.  Brokers hold retained publications
- one per topic - until replaced by a new publication.  A new
subscriber to a topic having a retained publication will receive the
current one, whereas a new subscriber to a topic carrying event data
will receive the next published message.

   The approach described here permits efficient management of
retained publications in a distributed network of brokers where
application programs can publish or subscribe at any node of the
network.  Publications are only propagated to those brokers that
have matching subscriptions.  When a broker loses all its
subscriptions to a topic for which it has a retained publication, it
removes the retained publication unless it was the broker that
originated the retained publication.

   The brokers propagate new subscriptions to each other and
start to receive the next available messages.  However, in the case
of retained publications, the broker may or may not have a copy,
depending on whether it already has an overlapping subscription,
possibly from another subscriber.  Hence, one of its neighbours must
send it a copy of any matching retained publi...