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, you need to be familiar with matters such as:
- How channels operate
- How to find their status
- How to use channel exits
These topics are all discussed in the WebSphere MQ Intercommunication book and the
advice given there is generally applicable to cluster channels, but you might
want to give some special consideration to the following:
- 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.
- 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.
- 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, you 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(R) Registry. See the WebSphere MQ System Administration Guide Guide for more information.