Remote topic views versus fan-out

Diffusion offers two ways to share topic data between servers that are not in the same cluster:

Remote topic views

A remote topic view uses the existing topic view mechanism to map part of the topic tree from a remote (or primary) server to a secondary server.

A remote topic view can be combined with the other capabilities of topic views, enabling sophisticated dynamic mapping and transformation of topics, as well as delayed or throttled feeds.

Remote topic views are configured dynamically with the API or management console and the configuration is automatically shared within a cluster, whereas fan-out requires file-based configuration.

Missing topic notifications can be propagated by remote servers if a missing topic notification filter is specified for the remote server that matches the path prefix of a subscription selector that matches no topics on the secondary server.

Though providing powerful mapping capabilities, remote servers do have a memory overhead at the secondary server as it is necessary to hold the value of each topic selected by topic views in the secondary server (though not within the topic tree). In the case where simple one-to-one mapping is all that is required (topic A at the primary becomes topic A at the secondary), fan-out may be more efficient.

Fan-out

Fan-out is used to replicate topics from a remote (or primary) server to a secondary server where the fan-out link is configured in the Server.xml configuration at the secondary server. They cannot be configured dynamically and need to be configured at each cluster member if operating within a secondary cluster.

Missing topic notifications can be propagated by fan-out links if a subscription selector matches no topics on the secondary server and the selector intersects with the fan-out link selector.

Unlike remote servers, fan-out has no memory overhead other than that for the replicated topic. So when one-to-one mapping is all that is required fan-out would be more efficient. Simple topic views on the secondary server could still select fan-out topics as their source topics.