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Cluster channels

 

Although using clusters relieves you of the need to define channels (because WebSphere MQ defines them for you), the same channel technology used in distributed queuing is used for communication between queue managers in a cluster. To understand about cluster channels, we need to be familiar with matters such as:

These topics are all discussed in the WebSphere MQ Intercommunications book and the advice given there is generally applicable to cluster channels, but you might want to give some special consideration to the following:

  1. When you are defining cluster-sender channels and cluster-receiver channels choose a value for HBINT or KAINT that will detect a network or queue manager failure in a useful amount of time but not burden the network with too many heartbeat or keep alive flows. Bear in mind that choosing a short time, for example, less than about 10 seconds, will give false failures if your network sometimes slows down and introduces delays of this length.

  2. Set the BATCHHB value if you want to reduce the window for causing a marooned message because it has got "in doubt" on a failed channel. This is more likely to occur if the message traffic along the channel is sporadic with long periods of time between bursts of messages, and during which a network failure is likely. This is sometimes a situation that is artificially induced when testing fail over of cluster queue managers, and may not be relevant on the production systems.

  3. If the cluster-sender end of a channel fails and subsequently tries to restart before the heartbeat or keep alive has detected the failure, the restart is rejected if the cluster-receiver end of the channel has remained active. To avoid this, we can arrange for the cluster-receiver channel to be terminated and restarted, when a cluster-sender channel attempts to restart.

    On WebSphere MQ for z/OS

    Control this using the ADOPTMCA and ADOPTCHK parameters on ALTER QMGR. See the WebSphere MQ Script (MQSC) Command Reference for more information.

    On platforms other than z/OS

    Control this using the AdoptNewMCA, AdoptNewMCATimeout, and AdoptNewMCACheck attributes in the qm.ini file or the Windows NT Registry. See the WebSphere MQ System Administration Guide Guide for more information.

 

Parent topic:

Cluster-administration considerations


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