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Finding out about other publishers and subscribers

 

Brokers publish information about the publishers and subscribers that are registered with them. The information is published as a special set of topics, known as metatopics, within each supported stream. They are published as persistent messages, and use the default priority for the stream queue (at the last time the broker started).

Applications can subscribe to this information in the same way as they can register any other subscription. Whenever the information changes, brokers publish the changed information in the form of retained publications so that new subscribers to it receive the current state.

Metatopic command messages can be sent to a broker using the WebSphere MQ Programmable Command Format (PCF), which is described in Writing system management applications. Publications containing the metatopic data are sent in PCF format, as are any broker response messages. This is illustrated in the Sample program for administration information.

Alternatively, metatopic command messages can be sent with the Rules and Formatting header (RFH), which is described in Format of command messages. In this case any broker response messages are in RFH format, but publications containing the metatopic data are sent in PCF format.

This chapter discusses the following topics:




 

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