What queue depth events are

Queue depth events are related to the queue depth, that is, the number of messages on the queue. The types of queue depth events are:

• Queue Depth High events, which indicate that the queue depth has increased to a predefined threshold called the Queue Depth High limit.

• Queue Depth Low events, which indicate that the queue depth has decreased to a predefined threshold called the Queue Depth Low limit.

• Queue Full events, which indicate that the queue has reached its maximum depth, that is, the queue is full.

A Queue Full Event is generated when an application attempts to put a message on a queue that has reached its maximum depth. Queue Depth High events give advance warning that a queue is filling up. This means that having received this event, the system administrator should take some preventive action. If this action is successful and the queue depth drops to a 'safe' level, the queue manager can be configured to generate a Queue Depth Low event indicating an 'all clear' state.

Figure 8 shows a graph of queue depth against time in such a case. The preventive action was (presumably) taken between T(2) and T(3) and continues to have effect until T(4) when the queue depth is well inside the 'safe' zone.

 

Shared queues and queue depth events (WebSphere MQ for z/OS)

When a queue depth event occurs on a shared queue, the queue managers in the queue-sharing group produce an event message, if the queue manager attribute PERFMEV is set to ENABLED. If PERFMEV is set to DISABLED on some of the queue managers, event messages are not produced by those queue managers, making event monitoring from an application more difficult. To avoid this, give each queue manager the same setting for the PERFMEV attribute. This event message represents the individual usage of the shared queue by each queue manager. If a queue manager performs no activity on the shared queue, various values in the event message are null or zero. Null event messages:

• Allow you to ensure there is one event message for each active queue manager in a queue-sharing group

• Can highlight cases where there has been no activity on a shared queue for a queue manager that produced the event message