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Queue managers and repositories

 

Every cluster has at least one (preferably two) queue managers holding full repositories of information about the queue managers, queues, and channels in a cluster. These repositories also contain requests from the other queue managers in the cluster for updates to the information.

The other queue managers each hold a partial repository, containing information about the subset of queues and queue managers with which they need to communicate. The queue managers build up their partial repositories by making inquiries when they first need to access another queue or queue manager, and by requesting that thereafter they be notified of any new information concerning that queue or queue manager.

Each queue manager stores its repository information in messages on a queue called SYSTEM.CLUSTER.REPOSITORY.QUEUE. The queue managers exchange repository information in messages on a queue called SYSTEM.CLUSTER.COMMAND.QUEUE.

Each queue manager that joins a cluster defines a cluster-sender (CLUSSDR) channel to one of the repositories. When it does this, it immediately learns which other queue managers in the cluster hold full repositories. From then on the queue manager can request information from any of the repositories. When the queue manager sends out any information about itself, for example when it creates a new queue definition, this information is sent to the chosen repository and also to one other repository (if there is one).

A full repository is updated when the queue manager hosting it receives new information from one of the queue managers that is linked to it. The new information is also sent to another repository, to reduce the risk of it being delayed if a repository queue manager is out of service. Because all the information is sent twice, the repositories have to discard duplicates. Each item of information carries a sequence number, which the repositories use to identify duplicates. All repositories are kept in step with each other by exchanging messages.

 

Parent topic:

Components of a cluster

qc10710_

 

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