The publish-and-subscribe model is a one-to-many model. In this type of messaging model the message initiates with the sender, and the message producer does not depend on message consumers receiving the message. The application sending the message is called the “message producer,” and the applications receiving the message are called “message consumers.” Message consumers establish subscriptions to register an interest in messages sent to a topic. A topic is the destination of this message model.
There are two types of subscriptions you can establish in this model:
Durable
Nondurable
A durable subscription retains messages for the message consumer even when the message consumer application is not connected. The message provider, not Adaptive Server, retains the message.
A nondurable subscription retains messages only when consumer applications are connected to the message provider.
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