Publish/subscribe: changes to proxy subscription propagation using PROXYSUB(FORCE)

In this release, when you configure a topic object with the parameter PROXYSUB set to FORCE, IBM® MQ automatically disables individual proxy subscriptions for topic strings below this point in the topic tree.

When PROXYSUB is set to FORCE, the following configuration is generated:
  • A wildcarded subscription is created that matches this topic object's topic string and all topic strings below this point in the topic tree.
  • This wildcarded subscription is propagated to all neighboring queue managers in a publish/subscribe topology.

In previous releases, setting PROXYSUB to FORCE did not automatically prevent individual proxy subscriptions being generated and propagated for topic strings below this point in the topic tree. In the current release, setting PROXYSUB to FORCE automatically disables individual proxy subscriptions for topic strings below this point in the topic tree.

In previous releases, to reduce the number of proxy subscriptions, you set the pscProxySubFlags tuning parameter to 1. This setting explicitly disabled all proxy subscriptions, except the wildcarded PROXYSUB(FORCE) subscription. In the current release, you no longer need to set the pscProxySubFlags parameter.

Note: You should not configure one topic object in the topic hierarchy below another topic object in different clusters or hierarchy streams. This is because publication flows across such a publish/subscribe network can be ambiguous, especially when combined with setting PROXYSUB to FORCE. Because previous releases propagated all proxy subscriptions regardless of the PROXYSUB setting, instances of such a configuration could go undetected. With the new behavior in this release, publications may not flow to the cluster or stream of the lower topic object. If such a configuration is detected, a warning message is written to the logs. The warning message ID depends on the platform:
  • Distributed[IBMi]On distributed systems and IBM i, AMQ5824 or AMQ5968
  • [z/OS]On z/OS®, CSQT824I or CSQT968I

To rectify the problem, either modify the topic hierarchy to remove the nested clusters or streams, or change both objects to have the same PROXYSUB setting.

For performance considerations when using PROXYSUB(FORCE), see Subscription performance in publish/subscribe networks.