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Subscription name and identity
Publish/Subscribe broker subscribers can be identified by their queue name, queue manager name, and optional correlation identifier. This, in conjunction with a topic, identifies an individual subscription, referred to here as the traditional identity of the subscription. An additional attribute to subscriptions, known as the subscription name, can be used instead of the traditional identity to reference a subscription.
The subscription name must be unique within the stream for which the subscription applies. On first registration, the traditional identity must be specified. The subscription name can be specified on the first registration or added to the subscription subsequently (at which time the traditional identity must also be specified to tie the two together). When the subscription name has been defined for the subscription, subsequent commands need specify only the subscription name to access (modify or deregister) the subscription. The underlying traditional identity for the subscription can now be changed by specifying the same subscription name with new traditional identity information on a Register Subscriber command.
A subscription name can be associated only with a single traditional identity at any one time within any stream of a broker (and in particular, with a single topic at a time), although it is possible to reuse a subscription name for a different subscription after the original has been deregistered, and it is possible to use the same subscription name in different streams on the same broker or on any stream of a different broker for different subscriptions. Subscription names are arbitrary character strings with no length limit. Subscription names that start with "MQ" are reserved for internal use.
If multiple applications require access to the same subscription, the broker can manage their access by using subscriber identities. A subscribing application can specify...
- A subscriber identity (an application-generated unique string) on a Register Subscriber
- Deregister Subscriber command to add or remove itself from the broker-managed list of interested applications.
The concepts of shared and exclusive access to a subscription are supported by the broker in much the same way as shared and exclusive access to WebSphere MQ objects is supported by a queue manager. The use of subscription identities on a subscription does not effect the publication of matching publications to that subscription; a single copy of each publication is still sent to the defined subscription queue no matter how many subscriber identities are currently registered. Deregistering with a subscription identity from a subscription does not delete the subscription unless the subscription identity list becomes empty as a result of removing the identity from that list. Identity names that start with "MQ" are reserved for internal use.
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