Adding a queue manager that hosts a queue

Add another queue manager to the cluster, to host another INVENTQ queue. Requests are sent alternately to the queues on each queue manager. No changes need to be made to the existing INVENTQ host.

Before you begin

Note: For changes to a cluster to be propagated throughout the cluster, at least one full repository must always be available. Ensure that your repositories are available before starting this task.

Scenario:

The INVENTORY cluster has been set up as described in Adding a queue manager to a cluster. It contains three queue managers; LONDON and NEWYORK both hold full repositories, PARIS holds a partial repository. The inventory application runs on the system in New York, connected to the NEWYORK queue manager. The application is driven by the arrival of messages on the INVENTQ queue.
A new store is being set up in Toronto. To provide additional capacity you want to run the inventory application on the system in Toronto as well as New York.
Network connectivity exists between all four systems.
The network protocol is TCP.

Note: The queue manager TORONTO contains only a partial repository. If you want to add a full-repository queue manager to a cluster, refer to Moving a full repository to another queue manager.

About this task

Follow these steps to add a queue manager that hosts a queue.

Procedure

Decide which full repository TORONTO refers to first.

Every queue manager in a cluster must refer to one or other of the full repositories. It gathers information about the cluster from a full repository and so builds up its own partial repository. It is of no particular significance which repository you choose. In this example, we choose NEWYORK. Once the new queue manager has joined the cluster it communicates with both of the repositories.
Define the CLUSRCVR channel.
Every queue manager in a cluster needs to define a cluster-receiver channel on which it can receive messages. On TORONTO, define a CLUSRCVR channel:
```
DEFINE CHANNEL(INVENTORY.TORONTO) CHLTYPE(CLUSRCVR) TRPTYPE(TCP)
CONNAME(TORONTO.CHSTORE.COM) CLUSTER(INVENTORY)
DESCR('Cluster-receiver channel for TORONTO')
```
The TORONTO queue manager advertises its availability to receive messages from other queue managers in the INVENTORY cluster using its cluster-receiver channel.
Define a CLUSSDR channel on queue manager TORONTO.
Every queue manager in a cluster needs to define one cluster-sender channel on which it can send messages to its first full repository. In this case choose NEWYORK. TORONTO needs the following definition:
```
DEFINE CHANNEL(INVENTORY.NEWYORK) CHLTYPE(CLUSSDR) TRPTYPE(TCP)
CONNAME(NEWYORK.CHSTORE.COM) CLUSTER(INVENTORY)
DESCR('Cluster-sender channel from TORONTO to repository at NEWYORK')
```
Optional: If you are adding to a cluster a queue manager that has previously been removed from the same cluster, check that it is now showing as a cluster member. If not, complete the following extra steps:
1. Issue the REFRESH CLUSTER command on the queue manager you are adding.
  This step stops the cluster channels, and gives your local cluster cache a fresh set of sequence numbers that are assured to be up-to-date within the rest of the cluster.
```
REFRESH CLUSTER(INVENTORY) REPOS(YES)
```
  Note: For large clusters, using the REFRESH CLUSTER command can be disruptive to the cluster while it is in progress, and again at 27 day intervals thereafter when the cluster objects automatically send status updates to all interested queue managers. See Refreshing in a large cluster can affect performance and availability of the cluster.
2. Restart the CLUSSDR channel
  (for example, using the START CHANNEL command).
3. Restart the CLUSRCVR channel.
Review the inventory application for message affinities.

Before proceeding, ensure that the inventory application does not have any dependencies on the sequence of processing of messages and install the application on the system in Toronto.
Define the cluster queue INVENTQ.
The INVENTQ queue, which is already hosted by the NEWYORK queue manager, is also to be hosted by TORONTO. Define it on the TORONTO queue manager as follows:
```
DEFINE QLOCAL(INVENTQ) CLUSTER(INVENTORY)
```

Results

Figure 1 shows the INVENTORY cluster set up by this task.

The diagram shows the INVENTORY cluster with four connected queue managers, TORONTO, LONDON, NEW YORK, and PARIS. INVENTQ is hosted on both NEW YORK and TORONTO. The inventory application is hosted on NEW YORK and LONDON. — Figure 1. The `INVENTORY` cluster with four queue managers

The INVENTQ queue and the inventory application are now hosted on two queue managers in the cluster. This increases their availability, speeds up throughput of messages, and allows the workload to be distributed between the two queue managers. Messages put to INVENTQ by either TORONTO or NEWYORK are handled by the instance on the local queue manager whenever possible. Messages put by LONDON or PARIS are routed alternately to TORONTO or NEWYORK, so that the workload is balanced.

This modification to the cluster was accomplished without you having to alter the definitions on queue managers NEWYORK, LONDON, and PARIS. The full repositories in these queue managers are updated automatically with the information they need to be able to send messages to INVENTQ at TORONTO. The inventory application continues to function if one of the NEWYORK or the TORONTO queue manager becomes unavailable, and it has sufficient capacity. The inventory application must be able to work correctly if it is hosted in both locations.

As you can see from the result of this task, you can have the same application running on more than one queue manager. You can clustering to distribution workload evenly.

An application might not be able to process records in both locations. For example, suppose that you decide to add a customer-account query and update application running in LONDON and NEWYORK. An account record can only be held in one place. You could decide to control the distribution of requests by using a data partitioning technique. You can split the distribution of the records. You could arrange for half the records, for example for account numbers 00000 - 49999, to be held in LONDON. The other half, in the range 50000 - 99999 , are held in NEWYORK. You could then write a cluster workload exit program to examine the account field in all messages, and route the messages to the appropriate queue manager.

What to do next

Now that you have completed all the definitions, if you have not already done so start the channel initiator on IBM® MQ for z/OS®. On all platforms, start a listener program on queue manager TORONTO. The listener program waits for incoming network requests and starts the cluster-receiver channel when it is needed.