Using WebSphere MQ cluster queues for input and output

When you design the WebSphere MQ network that underlies your WebSphere Event Broker broker domain, consider whether to use clusters.

The use of queue manager clusters brings the following significant benefits:

  1. Reduced system administration

    Clusters need fewer definitions to establish a network; you can set up and change your network more quickly and easily.

  2. Increased availability and workload balancing

    You can benefit by defining instances of the same queue to more than one queue manager, thus distributing the workload through the cluster.

If you use clusters with WebSphere Event Broker, consider the following:

For SYSTEM.BROKER queues:
The SYSTEM.BROKER queues are defined for you when you create WebSphere Event Broker components, and are not defined as cluster queues. Do not change this attribute.
For broker, Configuration Manager, and User Name Server connectivity:
If you define the queue managers that support your brokers, the Configuration Manager, and the User Name Server to a cluster, you can benefit from the simplified administration provided by WebSphere MQ clusters. You might find this particularly relevant for the brokers in a collective, which must all have WebSphere MQ interconnections.
For message flow input queues:
If you define an input queue as a cluster queue, consider the implications for the order of messages or the segments of a segmented message. The implications are the same as they are for any WebSphere MQ cluster queue. In particular, the application must ensure that, if it is sending segmented messages, all segments are processed by the same target queue, and therefore by the same instance of the message flow at the same broker.
For message flow output queues:
  • WebSphere Event Broker always specifies MQOO_BIND_AS_Q_DEF when it opens a queue for output. If you expect segmented messages to be put to an output queue, or want a series of messages to be handled by the same process, you must specify DEFBIND(OPEN) when you define that queue. This ensures that all segments of a single message, or all messages within a sequence, are put to the same target queue and are processed by the same instance of the receiving application.
  • If you create your own output nodes, specify MQOO_BIND_AS_Q_DEF when you open the output queue, and DEFBIND(OPEN) when you define the queue, if you need to guarantee message order, or to ensure a single target for segmented messages.
For publish/subscribe:
  • If the target queue for a publication is a cluster queue, you must deploy the publish/subscribe message flow to all the brokers on queue managers in the cluster. However, the cluster does not provide any of the failover function to the broker domain topology and function. If a broker to which a message is published, or a subscriber registers, is unavailable, the distribution of the publication or registration is not taken over by another broker.
  • When a client registers a subscription with a broker that is running on a queue manager that is a member of a cluster, the broker forwards a proxy registration to its neighbors within the broker domain; the registration details are not advertised to other members of the cluster.
  • A client might choose to become a clustered subscriber, so that its subscriber queue is one of a set of clustered queues that receive any given publication. In this case, when registering a subscription, use the name of an "imaginary" queue manager that is associated with the cluster; this is not the queue manager to which the publication will be sent, but an alias for the broker to use. As an administrative activity, a blank queue manager alias definition is made for this queue manager on the broker that satisfies this subscription for all clustered subscribers. When the broker publishes to a subscriber queue that names this queue manager, resolution of the queue manager name results in the publication being sent to any queue manager that hosts the subscriber cluster queue, and only one clustered subscriber receives the publication.

    For example, if the clustered subscriber queue was SUBS_QUEUE and the "imaginary" subscriber queue manager was CLUSTER_QM, the broker definition would be:

    DEFINE QREMOTE(CLUSTER_QM) RQMNAME(' ') RNAME(' ')

    This sends broker publications for SUBS_QUEUE on CLUSTER_QM to one instance of the cluster queue named SUBS_QUEUE anywhere in the cluster.

To understand more about clusters, and the implications of using cluster queues, see the WebSphere MQ Queue Manager Clusters book.

Related concepts
Message flows overview
Related tasks
Designing a message flow
Using WebSphere MQ shared queues for input and output (z/OS)
Creating a message flow
Defining message flow content
Related reference
Built-in nodes