Topic names cannot contain a wildcard character. For subscription expressions, no other template character ('*' 'or' # with any number of dots ".") is used. Usage of any other template character throws an exception in the look up call. All attempts to delete hierarchical topics are successful whether or not the topic has active publishers/subscribers present. It is, therefore, important to be careful so as not to delete hierarchical topics while they contain any active publishers or active subscribers.
A publisher cannot publish on multiple topics. A publisher has to specify the complete name of the hierarchical topic on which it wants to publish data. Creation of a publisher on a topic, which contains an asterisk '', throws an exception. Similarly, an exception is thrown if a publisher tries to publish on a topic which contains an asterisk ''. If a subscriber subscribes on hierarchical topics with a subscription expression and, while receiving messages, the administrator changes the ACL of one of the children of the hierarchy, then the subscriber will not be affected by this change. However, all new subscribers with a subscription expression will be affected.
There is a performance degradation associated with hierarchical topics. Users are, therefore, advised not to use hierarchical topics for applications where performance is a major requirement.
- A Hierarchical Topic is not supported by the following flags:
- UseOptimizedTCPReceive = true
- This implies that the Hierarchical Topic is not supported by the 7.2 runtime Layer.
2. Un-subscription for Hierarchical topics does not work. The User has to unsubscribe the subscribers created on behalf of hierarchical support manually, through Studio.