A non-durable subscriber is a message consumer that only receives messages that are published while the subscriber is active. Messages delivered while the subscriber is inactive are lost.
The information in this topic is relevant only when you are using publish/subscribe messaging over WebSphere MQ.
If consumer objects are not deleted before or during the closing of the connection, messages can be left on the broker queues for subscribers that are no longer active.
In this situation, the queues can be cleared of these messages using the Cleanup utility provided with WebSphere MQ Classes for JMS. Details of how to use this utility are provided in WebSphere MQ Using Java. You may also need to increase the queue depth of the subscriber queue if there are large numbers of messages left on this queue.