mqnotify

mqnotify is a feature of IBM MQ’s MQI (Message Queue Interface) that enables asynchronous notification for queue events. It lets a client program register an interest in a queue and be alerted when specified events occur, such as the arrival of a message on the queue or a change in the queue depth beyond configured thresholds.

Operation basics: A program opens a queue and supplies a notification specification to the MQI, registering a notification method and the events to monitor. The queue manager maintains the registration and, when a monitored event happens, delivers the notification to the registered client. The details of delivery depend on the platform and MQI version and can include signaling a waiting thread, invoking a user-written callback routine, or posting a message to a designated notification queue.

Delivery mechanisms: Notifications may be delivered through different channels, such as a callback function, a system event (for example, a thread wakeup), or a separate notification queue into which a message is placed. The chosen mechanism is specified as part of the registration and can vary by environment and MQI interface level.

Use cases: mqnotify supports event-driven architectures and low-latency processing by allowing applications to react promptly to queue activity. It is commonly used to trigger work handlers, monitor queue activity in real time, or implement responsive load management.

Limitations and considerations: Registering for notifications requires appropriate authority on the queue and access to the notification mechanism. Not all events may be reported under heavy load, and there may be limits on the number of concurrent registrations. Applications should design for potential missed events or coalesced notifications and handle security and resource implications of active notifications.

See also: IBM MQ, MQI, messaging triggers, asynchronous notifications.