22.1.3 Benefits of Using JMQ Notification

The JMQ notification plug-in, with Message Queue, provides the following benefits:

• Message Queue implements the JMS standard.

• With Message Queue, you can produce messages to a topic or a queue, or to both of these delivery methods. For a brief definition, see 22.1.3.1 Publishing to a Topic or a Queue.

• Message Queue offers enhanced load balancing during message distribution, especially when messages are produced to a queue.

• The JMQ notification plug-in allows you to configure up to five notification plug-ins. The different plug-ins can produce messages to a topic, to a queue, to the Event Notification Service, and so on. For details, see 22.1.3.2 Using Multiple JMQ Notification Plug-ins.

• Message Queue provides reliable delivery of notifications.

  For example, if you configure the JMQ notification plug-in to produce messages with the persistent flag enabled, the message remains in the Message Queue broker until a consumer receives it. The message is saved so that, if a server goes down, the message can be retrieved and made available to the appropriate consumer.

22.1.3.1 Publishing to a Topic or a Queue

A topic and queue use different messaging delivery patterns; each one can be configured in a Message Queue service.

Topic. When a message producer sends a message to a topic, a publish/subscribe architecture is used. In this broadcast pattern, a producer sends a message to a topic destination. Any number of consumers can be subscribed to this topic destination. Each consumer subscribed to the topic gets its own copy of the message. If no consumers are subscribed to the topic, the message is discarded.

The Event Notification Service also uses a publish/subscribe architecture; it is similar to the topic pattern defined in Message Queue.

Queue. When a message producer sends a message to a queue, a point-to-point architecture is used. In this pattern, a producer sends a message to a queue destination from which only one consumer can receive it. If several consumers are waiting for messages from the queue, only one subscriber will receive the message. If no consumers are waiting, the message is held until either the message times out, or a consumer expresses an interest in the queue.

Producing messages to a queue allows you to spread the message load across multiple consumers.

22.1.3.2 Using Multiple JMQ Notification Plug-ins

You can configure from one to five notification plug-ins.

Messaging Server provides a plug-in library at the following default location:

/opt/SUNWmsgsr/lib/libjmqnotify

You use the configutil utility to specify parameters for a plug-in and to point the plug-in to the library of executable code.

If you specify more than one plug-in, each plug-in produces notification messages independently of the others. For example, if two plug-ins are configured with a delete-message parameter, and a message is deleted from a user's mailbox, both plug-ins will produce a notification message.

By configuring multiple plug-ins, you can take advantage of different message-distribution patterns for different purposes. For example, you could configure three different plug-ins to produce messages

• To a queue (using Message Queue)

• To a topic (using Message Queue)

• To the Event Notification Service

22.1.3.3 Configuring Parameters for a Notification Plug-in

For each plug-in you configure, you must define a separate set of configutil parameters.

The parameters determine two kinds of information:

• The kinds of notification messages to produce. For example, enabling the LogUser parameter causes a notification message to be sent whenever a user logs in or out.

• Configuration information needed by Message Queue. For example, the jmqHost parameter identifies the IP address of the host where the Message Queue broker is running.

For instructions on how to configure a plug-in, see To Configure a JMQ Notification Plug-in.