CLWLRANK queue attribute

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.