MQTT supports a hierarchical topic namespace and allows you to subscribe to every topic in a namespace using a wildcard symbol such as #. Any MQTT messages that are sent to the broker and that satisfy the topic namespace are sent to the correlator.

A potential result of this may be that a single MQTT message that is sent to the broker is received more than once by the correlator. For example, assume that Apama subscribes to both of the following channels:

If a single MQTT message is sent to the broker using the topic name SENSOR/1, then this MQTT message will be received twice by the correlator. You should be aware of such situations and write your EPL accordingly to handle this.