In each cluster you must select at least one, preferably two, or possibly more of the queue managers to hold full repositories. A cluster can work quite adequately with only one full repository but using two improves availability. You interconnect the full repository queue managers by defining cluster-sender channels between them.
Figure 13 shows a typical 2-full repository topology. This is the topology used in the cluster shown in Figure 2.
When a queue manager sends out information about itself or requests information about another queue manager, the information or request is sent to two full repositories. A full repository named on a CLUSSDR definition handles the request whenever possible, but if the chosen full repository is not available another full repository is used. When the first full repository becomes available again it collects the latest new and changed information from the others so that they keep in step.
In very large clusters, containing thousands of queue managers, you might want to have more than two full repositories. Then you might have one of the following topologies. (These are only example topologies)
If all the full repository queue managers go out of service at the same time, queue managers continue to work using the information they have in their partial repositories. Clearly they are limited to using the information that they have. New information and requests for updates cannot be processed. When the full repository queue managers reconnect to the network, messages are exchanged to bring all repositories (both full and partial) back up-to-date.
The full repositories republish the publications they receive through the manually-defined CLUSSDR channels, which must point to other full repositories in the cluster. You must make sure that a publication received by any full repository ultimately reaches all the other full repositories. You do this by manually defining CLUSSDR channels between the full repositories. The more interconnection of full repositories you have, the more robust the cluster.
Having only two full repositories is sufficient for all but very exceptional circumstances.
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