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# About Topics

A topic is a metadata tag that you can apply to events in order to categorize them. Transformation Hub ships with several pre-set topics, and you can define any number of additional topics as needed.

A topic includes these components:

- Name: The name of the topic.
  Note: ArcSight Avro is the displayed name for the type name event-avro for the ArcSight avro topic.
- Topic Type: The type of topic CEF (routable) ArcSight Avro (routable) BINARY (not routable) RAW (not routable) SYSLOG (not routable).
- Partition Count: A segment of a topic. There can be one or more partitions for each topic. The number of partitions limits the maximum number of consumers in a consumer group.
- Replication Factor: The number of copies of each partition in a topic. Each replica is created across one Transformation Hub node. For example, a topic with a replication factor of 3 would have 3 copies of each of its partitions, across 3 Transformation Hub nodes.

You can only use ArcMC to add topics (not delete them). The Edit option is only available for topics with a null topic type (topics not created by ArcMC. e.g. Kafka manager) and it allows the user to modify the Topic Type value.

To set the type for existing topics (only for topics not created by ArcMC. e.g. Kafka manager), users can access the List of Topics page located in Configuration Management > Transformation Hub > Topics. This page will display detailed information for Topic Name, Topic Type, Routable Topic, Partitions Count, and Replication Factor. This option is only available for Transformation Hub 3.4+.

For more information on managing topic partitions and replication, please see Managing Topics.