WebSphere WebSphere Application Server Network Deployment, Version 6.0.x Operating Systems: AIX, HP-UX, Linux, Solaris, Windows

Workload sharing with publish/subscribe messaging

You can set whether durable subscriptions are shared between subscribers in a cluster.

In nondurable publish/subscribe messaging, such as information feeds, all subscribers typically receive a copy of each matching publication. Where durable subscriptions are used, for example to handle incoming requests, this may not be the desired behavior. In order to spread request workload across a cluster of subscribers, the incoming publications must be divided between the subscribers, instead of every subscriber receiving every publication.

A durable subscription has a home messaging engine within a bus, which manages the state of the durable subscription using a localization point, similar in principle to a queue destination. This localization point cannot be partitioned across a cluster.

Because the subscribers (which typically may be message-driven beans) are in a cluster they are likely to be using the same Connection Factory, so will have the same client identifier. In general, two clients trying to use the same client identifier and subscription name would be treated as an error condition, but for durable subscriptions, you can control whether multiple clients with the same client identifier are treated as instances of the "same" consumer or whether they represent a configuration error. This is controlled using the Share durable subscriptions attribute of the Connection Factory that is used by the clients.

A shared durable subscription is one which can be simultaneously accessed by multiple cooperating clients. Because the clients are treated as cooperating rather than contending, each message is delivered to one client. If clients are not allowed to share the durable subscription, that is, the Share durable subscriptions property disallows concurrent access because it is set to "never" or "in a cluster", then the bus will not accept an attempt by a client to create a consumer session to a durable subscription that is already in use, even if the client has the same client identifier as the one that already has a consumer.

Related concepts
JMS connection factories and service integration
Related tasks
Configuring shared durable subscriptions

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Last updated: 15 Mar 2007
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