Queue-sharing groups and clusters

Shared queues can be cluster queues and queue managers in a queue-sharing group can also be cluster queue managers.

On IBM® MQ for z/OS® you can group queue managers into queue-sharing groups. A queue manager in a queue-sharing group can define a local queue that is to be shared by up to 32 queue managers.

Shared queues can also be cluster queues. Furthermore, the queue managers in a queue-sharing group can also be in one or more clusters.

You can define VTAM generic resources or Dynamic Domain Name Server (DDNS) generic names. You can define connection names using generic names. However, when you create a cluster-receiver definition, do not use a generic connection name.

The problem with using generic connection names for cluster-receiver definitions is as follows: If you define a CLUSRCVR with a generic CONNAME there is no guarantee that your CLUSSDR channels point to the queue managers you intend. Your initial CLUSSDR might end up pointing to any queue manager in the queue sharing group, not necessarily one that hosts a full repository. If a channel starts trying a connection again, it might reconnect to a different queue manager with the same generic name, disrupting the flow of messages.

A CLUSRCVR channel that uses the group listener port can not be started because, if this were the case, it would not be possible to tell which queue manager the CLUSRCVR would connect to each time. The cluster system queues on which information is kept about the cluster are not shared. Each queue manager has its own.

Cluster channels are used not only to transfer application messages but internal system messages about the setup of the cluster. Each queue manager in the cluster must receive these internal system messages to participate properly in clustering, so needs its own unique CLUSRCVR channel on which to receive them.

A shared CLUSRCVR could start on any queue manager in the queue sharing group (QSG) and so lead to an inconsistent supply of the internal system messages to the QSG queue managers, meaning none can properly participate in the cluster. To ensure no shared CLUSRCVR channels can be used, any attempt fails with the CSQX502E message.