Defining cluster queues

A cluster queue is a queue that is hosted by a cluster queue manager and made available to other queue managers in the cluster.Define a cluster queue as a local queue on the cluster queue manager where the queue is hosted. Specify the name of the cluster the queue belongs to.

The following example shows a runmqsc command to define a cluster queue with the CLUSTER option: 
DEFINE QLOCAL(Q1) CLUSTER(SALES)

A cluster queue definition is advertised to other queue managers in the cluster. The other queue managers in the cluster can put messages to a cluster queue without needing a corresponding remote-queue definition. A cluster queue can be advertised in more than one cluster by using a cluster namelist.

When a queue is advertised, any queue manager in the cluster can put messages to it. To put a message, the queue manager must find out, from the full repositories, where the queue is hosted. Then it adds some routing information to the message and puts the message on a cluster transmission queue.

A cluster queue can be a queue that is shared by members of a queue sharing group in IBM MQ for z/OS .


Binding

We can create a cluster in which more than one queue manager hosts an instance of the same cluster queue. Make sure that all the messages in a sequence are sent to the same instance of the queue. We can bind a series of messages to a particular queue by using the MQOO_BIND_ON_OPEN option on the MQOPEN call.


Cluster transmission queues

A queue manager can store messages for other queue managers in a cluster on multiple transmission queues. We can configure a queue manager to store messages on multiple cluster transmission queues in two different ways. If you set the queue manager attribute DEFCLXQ to CHANNEL, a different cluster transmission queue is created automatically from SYSTEM.CLUSTER.TRANSMIT.MODEL.QUEUE for each cluster-sender channel. If you set the CLCHNAME transmission queue option to match one or more cluster-senders channel, the queue manager can store messages for the matching channels on that transmission queue.

A message for a cluster queue on a different queue manager is placed upon a cluster transmission queue before being sent. A cluster-sender channel transfers the messages from a cluster transmission queue to cluster-receiver channels on other queue managers. By default, one system defined cluster transmission queue holds all the messages that are to be transferred to other cluster queue managers. The queue is called SYSTEM.CLUSTER.TRANSMIT.QUEUE. A queue manager that is part of a cluster can send messages on this cluster transmission queue to any other queue manager in the same cluster.

A definition for the single SYSTEM.CLUSTER.TRANSMIT.QUEUE queue is created by default on every queue manager except on z/OS. On z/OS, the definition can be defined with the supplied sample CSQ4INSX.

We can configure a queue manager to transfer messages to other clustered queue managers using multiple transmission queues. We can define additional cluster transmission queues manually, or have the queue manager create the queues automatically.

To have the queues created automatically by the queue manager, change the queue manager attribute DEFCLXQ from SCTQ to CHANNEL. The result is the queue manager creates an individual cluster transmission queue for each cluster-sender channel that is created. The transmission queues are created as permanent dynamic queues from the model queue, SYSTEM.CLUSTER.TRANSMIT.MODEL.QUEUE. The name of each permanent dynamic queue is SYSTEM.CLUSTER.TRANSMIT. ChannelName. The name of the cluster-sender channel that each permanent dynamic cluster transmit queue is associated with is set in the local transmission queue attribute CLCHNAME. Messages for remote clustered queue managers are placed on the permanent dynamic cluster transmission queue for the associated cluster-sender channel, rather than on SYSTEM.CLUSTER.TRANSMIT.QUEUE.

To create the cluster transmission queues manually, create a local queue with the USAGE attribute set to XMITQ, and the CLCHNAME attribute set to a generic channel name that resolves to one or more cluster-sender channels; see ClusterChannelName. If you create cluster transmission queues manually, you have the choice of associating the transmission queue with a single cluster-sender channel, or with multiple cluster-sender channels. The CLCHNAME attribute is a generic-name, which means we can place multiple wildcard characters, *, in the name.

Except for the initial cluster-sender channels that you create manually to connect a queue manager to a full repository, cluster-sender channels are created automatically. They are created automatically when there is a message to transfer to a cluster queue manager. They are created with the same name as the name of the cluster-receiver channel that receives cluster messages for that particular cluster on the destination queue manager.

If you follow a naming convention for cluster-receiver channels, it is possible to define a generic value for CLCHNAME that filters different kinds of cluster messages to different transmission queues. For example, if you follow the naming convention for cluster-receiver channels of ClusterName. QmgrName, then the generic name ClusterName.* filters messages for different clusters onto different transmission queues. We must define the transmission queues manually, and set CLCHNAME in each transmission queue to ClusterName.*.

Changes to the association of cluster transmission queues to cluster-sender channels do not take immediate effect. The currently associated transmission queue that a cluster-sender channel is servicing might contain messages that are in the process of being transferred by the cluster-sender channel. Only when no messages on the currently associated transmission queue are being processed by a cluster-sender channel, can the queue manager change the association of the cluster-sender channel a different transmission queue. This can occur either when no messages remain on the transmission queue to be processed by the cluster-sender channel, or when processing of messages is suspended and the cluster-sender channel has no in-flight messages. When this happens, any unprocessed messages for the cluster-sender channel are transferred to the newly associated transmission queue, and the association of the cluster-sender channel changes.

We can create a remote queue definition that resolves to a cluster transmission queue. In the definition, queue manager QMX is in the same cluster as the local queue manager, and there is no transmission queue, QMX. 
DEFINE QREMOTE(A) RNAME(B) RQMNAME(QMX)
During queue name resolution, the cluster transmission queue takes precedence over the default transmission queue. A message put to A is stored on the cluster transmission queue and then sent to the remote queue B on QMX.

Queue managers can also communicate with other queue managers that are not part of a cluster. We must define channels and a transmission queue to the other queue manager, in the same way as in a distributed-queuing environment.

Note: Applications must write to queues that resolve to the cluster transmission queue, and must not write directly to the cluster transmission queue.


Auto definition of remote queues

A queue manager in a cluster does not need a remote-queue definition for remote queues in the cluster. The cluster queue manager finds the location of a remote queue from the full repository. It adds routing information to the message and puts it on the cluster transmission queue. IBM MQ automatically creates a definition equivalent to a remote-queue definition so that the message can be sent.

We cannot alter or delete an automatically created remote-queue definition. However, by using the DISPLAY QUEUE runmqsc command with the CLUSINFO attribute, we can view all of the local queues on a queue manager as well as all of the cluster queues, including cluster queues on remote queue managers. For example: 
DISPLAY QUEUE(*) CLUSINFO
Parent topic: Defining components of a cluster


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