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How many full repositories should you have in a WebSphere MQ cluster? The Queue Manager Clusters manual says “preferably two” and “Having only two full repositories is sufficient for all but very exceptional circumstances” (see doc).
The reason for having two rather one is for availability reasons (one is a single point of failure). Single point of failure is probably somewhat of an overstatement, as the impact of all full repositories being unavailable is that definitional changes (e.g. define/alter cluster queues or cluster queue receiver channels) cannot be shared with the cluster.
Application messages between available cluster queue managers can still flow when full repositories are not available, so the impact is to cluster object changes rather directly on application traffic.
A fictional encounter containing useful information about WebSphere MQ and affinities
—— Scene 1/1 —————
<Herd of buffalo exit stage right. A few seconds later, Ian enters stage left and Dylbert enters stage top>
|Dylbert:||Hi Ian. Got a minute? I have a quick MQ clustering question for you.|
|Ian:||Hey Dylbert. Sure I have a minute, fire away.|
|Dylbert:||Thanks. How should I stop my queue manager, QM1? It’s in a cluster and I want to bring it down for maintenance.|