Cluster workload balancing - queue attributes

An alphabetical list of queue attributes used in cluster workload balancing.

CLWLPRTY

The CLWLPRTY queue attribute specifies the priority of local, remote, or alias queues for cluster workload distribution. The value must be in the range 0-9, where 0 is the lowest priority and 9 is the highest.

Use the CLWLPRTY queue attribute to set a preference for destination queues. IBM® MQ selects the destinations with the highest priority before selecting destinations with the lowest cluster destination priority. If there are multiple destinations with the same priority, it selects the least recently used destination.

IBM MQ obtains the priority of queue managers after checking channel status. Only available queue managers are candidates for selection.

Note:

The availability of a remote queue manager is based on the status of the channel to that queue manager. When channels start, their state changes several times, with some of the states being less preferential to the cluster workload management algorithm. In practice this means that lower priority (backup) destinations can be chosen while the channels to higher priority (primary) destinations are starting.

If you need to ensure that no messages go to a backup destination, do not use CLWLPRTY. Consider using separate queues, or CLWLRANK with a manual switch over from the primary to back up.

If there are two possible destinations, you can use this attribute to allow failover. The highest priority queue manager receives requests, lower priority queue managers act as reserves. If the highest priority queue manager fails, then the next highest priority queue manager that is available, takes over.

CLWLRANK

The CLWLRANK queue attribute specifies the rank of a local, remote, or alias queue for cluster workload distribution. The value must be in the range 0-9, where 0 is the lowest rank and 9 is the highest.

Use the CLWLRANK queue attribute if you want control over the final destination for messages sent to a queue manager in another cluster. When you set CLWLRANK, messages take a specified route through the interconnected clusters towards a higher ranked destination.

For example, you might have defined two identically configured gateway queue managers to improve the availability of a gateway. Suppose you have defined cluster alias queues at the gateways for a local queue defined in the cluster. If the local queue becomes unavailable, you intend the message to be held at one of the gateways pending the queue becoming available again. To hold the queue at a gateway, you must define the local queue with a higher rank than the cluster alias queues at the gateway.

If you define the local queue with the same rank as the queue aliases and the local queue is unavailable, the message travels between the gateways. On finding the local queue unavailable the first gateway queue manager routes the message to the other gateway. The other gateway tries to deliver the message to the target local queue again. If the local queue is still unavailable, it routes the message back to the first gateway. The message keeps being moved back and forth between the gateways until the target local queue became available again. By giving the local queue a higher rank, even if the queue is unavailable, the message is not rerouted to a destination of lower rank.

IBM MQ obtains the rank of queues before checking channel status. Obtaining the rank before checking channel status means that even non-accessible queues are available for selection. It allows messages to be routed through the network even if the final destination is unavailable.

If you used the priority attribute IBM MQ selects between available destinations. If a channel is not available to the destination with the highest rank, the message is held on the transmission queue. It is released when the channel becomes available. The message does not get sent to the next available destination in the rank order.

CLWLUSEQ

The CLWLUSEQ queue attribute specifies whether a local instance of a queue is given preference as a destination over other instances in a cluster.

The CLWLUSEQ queue attribute is valid only for local queues. It only applies if the message is put by an application, or a channel that is not a cluster channel.

LOCAL: The local queue is the only target of MQPUT, providing the local queue is put enabled. MQPUT behavior depends upon the cluster workload management.
QMGR: The behavior is as specified by the CLWLUSEQ queue manager attribute.
ANY: MQPUT treats the local queue the same as any other instance of the queue in the cluster for workload distribution.