Clustering with intra-group queuing (multiple delivery paths)
It is possible to configure queue managers so that they are in a cluster as well as in a queue sharing group.
When messages are sent to a cluster queue and the local and remote destination queue managers are in the same queue sharing group, intra-group queuing is used for the delivery of small messages (using the SYSTEM.QSG.TRANSMIT.QUEUE), and the delivery of large messages if intra-group queuing supports the size of the message. Also, the SYSTEM.CLUSTER.TRANSMIT.QUEUE is used for the delivery of messages to any queue manager that is in the cluster, but outside the queue sharing group. The following diagram illustrates this configuration (the channel initiators are not shown).
The diagram shows:
- Four z/OS® queue managers QMG1, QMG2, QMG3, and QMG4 configured in a cluster CLUS1.
- Queue managers QMG1, QMG2, and QMG3 configured in a queue sharing group SQ26.
- IGQ agents running on queue managers QMG2 and QMG3.
- The local SYSTEM.CLUSTER.TRANSMIT.QUEUE defined in QMG1.Note: For clarity, the SYSTEM.CLUSTER.TRANSMIT.QUEUE on the other queue managers not shown.
- The shared SYSTEM.QSG.TRANSMIT.QUEUE defined in the CF, which is in an IBM MQ structure configured with the CFLEVEL(3) RECOVER(YES) attribute.
- Cluster channels TO.QMG2 (connecting QMG1 to QMG2), TO.QMG3 (connecting QMG1 to QMG3), and TO.QMG4 (connecting QMG1 to QMG4).
- Cluster queue CLUSQ1 being hosted on queue managers QMG2, QMG3, and QMG4.
Assume that the requesting application opens the cluster queue with the MQOO_BIND_NOT_FIXED option, so that the target queue manager for the cluster queue is selected at put time.
If the selected target queue manager is QMG2:
- All large messages put by the requesting application are:
- Put to the SYSTEM.CLUSTER.TRANSMIT.QUEUE on QMG1, because SYSTEM.QSG.TRANSMIT.QUEUE is in a CFLEVEL(3) structure; therefore supports messages only up to 63 KB in size.
- Transferred to cluster queue CLUSQ1 on QMG2 using cluster channel TO.QMG2
- All small messages put by the requesting application are
- Put to the shared transmission queue SYSTEM.QSG.TRANSMIT.QUEUE. This queue is in a structure configured with the RECOVER(YES) attribute, so is used for both persistent, and non-persistent, small messages.
- Retrieved by the IGQ agent on QMG2
- Put to the cluster queue CLUSQ1 on QMG2
If the selected target queue manager is QMG4:
- Because QMG4 is not a member of queue sharing group SQ26, all messages put by the requesting
application are
- Put to the SYSTEM.CLUSTER.TRANSMIT.QUEUE on QMG1
- Transferred to cluster queue CLUSQ1 on QMG4 using cluster channel TO.QMG4
Points to note
- The requesting application does not need to be aware of the underlying mechanism used for the delivery of messages.
- A potentially faster delivery mechanism is achieved for the transfer of small non-persistent messages between queue managers in a queue sharing group (even if the same queue managers are in a cluster).
- Multiple paths are available for message delivery (that is, both the cluster route and the intra-group queuing route).
- The intra-group queuing route, being potentially faster, is selected in preference to the cluster route. Depending on the message characteristics, message delivery might be divided across the two paths. Hence, messages might be delivered out of sequence. It is important to note that this delivery is possible without regard to the MQOO_BIND_* option specified by the application. Intra-group queuing distributes messages in the same way as clustering does, depending on whether the MQOO_BIND_NOT_FIXED, MQOO_BIND_ON_OPEN, MQOO_BIND_ON_GROUP, or MQOO_BIND_AS_Q_DEF is specified on open.
- When a route has been selected, and messages have been placed on to the transmission queues, only the selected route is used for message delivery. Any unprocessed messages on the SYSTEM.QSG.TRANSMIT.QUEUE are not diverted to the SYSTEM.CLUSTER.TRANSMIT.QUEUE.