使用主题（发布和订阅），何时将邮件从主题中删除？

Question

Say there is a topic many MQ clients are connected to in order to receive messages.

My question is when will the MQ server remove the message from the topic?

Answer 1

There are two points here:

First: MQ queue manager will deliver publications to all subscribers registered for that topic. If a subscription is non-durable, then the publication is delivered only if the subscriber is active. If a subscription is durable, then the publication will be put into the destination (basically a queue) specified by the subscription. If the durable subscriber is active, the publication may be picked up immediately else it may be picked up later. Once the queue manager delivers the publication to all registered subscribers, the publication is discarded.

Second: Queue manager will retain a copy of the publication if the publisher tells it to do so. In this case the publication is retained by queue manager until a publisher publishes another publication on the same topic and tells again to retain the publication.