Creating a queue manager

A queue manager manages the resources associated with it, in particular the queues that it owns. It provides queuing services to applications for Message Queuing Interface (MQI) calls and commands to create, modify, display, and delete WebSphere MQ objects.

Before you can do anything with messages and queues, you must create and start at least one queue manager and its associated objects. To create a queue manager, use the WebSphere MQ control command crtmqm (described in crtmqm (create queue manager)). The crtmqm command automatically creates the required default objects and system objects (described in "System default objects"). Default objects form the basis of any object definitions that you make; system objects are required for queue manager operation. When you have created a queue manager and its objects, use the strmqm command to start the queue manager.

Guidelines for creating queue managers

Before you can create a queue manager, there are several points you need to consider (especially in a production environment). Work through the following checklist:

Naming conventions

Use uppercase names so that you can communicate with queue managers on all platforms. Remember that names are assigned exactly as you enter them. To avoid the inconvenience of lots of typing, do not use unnecessarily long names.

Specify a unique queue manager name

When you create a queue manager, ensure that no other queue manager has the same name anywhere in your network. Queue manager names are not checked when the queue manager is created, and names that are not unique prevent you from creating channels for distributed queuing.

One way of ensuring uniqueness is to prefix each queue manager name with its own unique node name. For example, if a node is called ACCOUNTS, you can name your queue manager ACCOUNTS.SATURN.QUEUE.MANAGER, where SATURN identifies a particular queue manager and QUEUE.MANAGER is an extension you can give to all queue managers. Alternatively, you can omit this, but note that ACCOUNTS.SATURN and ACCOUNTS.SATURN.QUEUE.MANAGER are different queue manager names.

If you are using WebSphere MQ for communication with other enterprises, you can also include your own enterprise name as a prefix. This is not done in the examples, because it makes them more difficult to follow.

Note:

Queue manager names in control commands are case-sensitive. This means that you are allowed to create two queue managers with the names jupiter.queue.manager and JUPITER.queue.manager. However, it is better to avoid such complications.

Limit the number of queue managers

You can create as many queue managers as resources allow. However, because each queue manager requires its own resources, it is generally better to have one queue manager with 100 queues on a node than to have ten queue managers with ten queues each.

In production systems, many nodes are run with a single queue manager, but larger server machines might run with multiple queue managers.

Specify a default queue manager

Each node should have a default queue manager, though it is possible to configure WebSphere MQ on a node without one. The default queue manager is the queue manager that applications connect to if they do not specify a queue manager name in an MQCONN call. It is also the queue manager that processes MQSC commands when you invoke the runmqsc command without specifying a queue manager name.

Specifying a queue manager as the default replaces any existing default queue manager specification for the node.

Changing the default queue manage can affect other users or applications. The change has no effect on currently-connected applications, because they can use the handle from their original connect call in any further MQI calls. This handle ensures that the calls are directed to the same queue manager. Any applications connecting after you have changed the default queue manager connect to the new default queue manager. This might be what you intend, but you should take this into account before you change the default.

Creating a default queue manager is described in Creating a default queue manager.

Specify a dead-letter queue

The dead-letter queue is a local queue where messages are put if they cannot be routed to their intended destination.

It is important to have a dead-letter queue on each queue manager in your network. If you do not define one, errors in application programs might cause channels to be closed, and replies to administration commands might not be received.

For example, if an application tries to put a message on a queue on another queue manager, but gives the wrong queue name, the channel is stopped and the message remains on the transmission queue. Other applications cannot then use this channel for their messages.

The channels are not affected if the queue managers have dead-letter queues. The undelivered message is simply put on the dead-letter queue at the receiving end, leaving the channel and its transmission queue available.

When you create a queue manager, use the -u flag to specify the name of the dead-letter queue. You can also use an MQSC command to alter the attributes of a queue manager that you have already defined to specify the dead-letter queue to be used. See Altering queue manager attributes for an example of the MQSC command ALTER.

Specify a default transmission queue

A transmission queue is a local queue on which messages in transit to a remote queue manager are queued before transmission. The default transmission queue is the queue that is used when no transmission queue is explicitly defined. Each queue manager can be assigned a default transmission queue.

When you create a queue manager, use the -d flag to specify the name of the default transmission queue. This does not actually create the queue; you have to do this explicitly later on. See Working with local queues for more information.

Specify the logging parameters you require

You can specify logging parameters on the crtmqm command, including the type of logging, and the path and size of the log files.

In a development environment, the default logging parameters should be adequate. However, you can change the defaults if, for example:

• You have a low-end system configuration that cannot support large logs.
• You anticipate a large number of long messages being on your queues at the same time.
• You anticipate a lot of persistent messages passing through the queue manager.

Once you have set the logging parameters, some of them can only be changed by deleting the queue manager and re-creating it with the same name but with different logging parameters.

For more information about logging parameters, see Chapter 14, Recovery and restart.

Installing multiple queue managers

If you install multiple queue managers with different logical volumes for each queue manager, the ftok function might cause shared memory problems. The ftok function calculates the shared memory key from the node and the minor number of the housing logical volume. On AIX, shared memory problems can occur if two queue managers are installed in an HACMP environment with different logical volumes that have identical minor device numbers.

These shared memory problems do not occur if the different logical volumes are created such that they have different minor device numbers.

Creating a default queue manager

You create a default queue manager using the crtmqm command with the -q flag. The following crtmqm command:

• Creates a default queue manager called SATURN.QUEUE.MANAGER
• Creates the default and system objects
• Specifies the names of both a default transmission queue and a dead-letter queue

crtmqm -q -d MY.DEFAULT.XMIT.QUEUE -u SYSTEM.DEAD.LETTER.QUEUE  SATURN.QUEUE.MANAGER

where:

-q

Indicates that this queue manager is the default queue manager.

-d MY.DEFAULT.XMIT.QUEUE

Is the name of the default transmission queue to be used by this queue manager.

Note:

WebSphere MQ does not create a default transmission queue for you; you have to define it yourself.

-u SYSTEM.DEAD.LETTER.QUEUE

Is the name of the default dead-letter queue created by WebSphere MQ on installation.

SATURN.QUEUE.MANAGER

Is the name of this queue manager. This must be the last parameter specified on the crtmqm command.

The complete syntax of the crtmqm command is shown in crtmqm (create queue manager).

The system and default objects are listed in Appendix A, System and default objects.

Making an existing queue manager the default

You can make an existing queue manager the default queue manager. The way you do this depends on the platform you are using.

Windows systems

On Windows systems, use the WebSphere MQ Services snap-in to display the properties of the queue manager, and check the Make queue manager the default box. You need to stop and restart the queue manager for the change to take effect.

UNIX systems

When you create a default queue manager, its name is inserted in the Name attribute of the DefaultQueueManager stanza in the WebSphere MQ configuration file (mqs.ini). The stanza and its contents are automatically created if they do not exist.

• To make an existing queue manager the default, change the queue manager name on the Name attribute to the name of the new default queue manager. You must do this manually, using a text editor.
• If you do not have a default queue manager on the node, and you want to make an existing queue manager the default, create the DefaultQueueManager stanza with the required name yourself.
• If you accidentally make another queue manager the default and want to revert to the original default queue manager, edit the DefaultQueueManager stanza in mqs.ini, replacing the unwanted default queue manager with that of the one you want.

See Chapter 9, Configuring WebSphere MQ for information about configuration files.

When you have changed the configuration information, stop the queue manager and restart it. See Stopping a queue manager for information about how to do this.

Backing up configuration files after creating a queue manager

WebSphere MQ configuration information is stored in the Registry for Windows systems, and in configuration files on UNIX systems.

Windows systems

If you use WebSphere MQ for Windows, configuration information is stored in the Windows Registry. Use the WebSphere MQ Services snap-in or the amqmdain command to make changes to the Registry.

UNIX systems

There are two types of configuration file:

• When you install the product, the WebSphere MQ configuration file (mqs.ini) is created. It contains a list of queue managers that is updated each time you create or delete a queue manager. There is one mqs.ini file per node.
• When you create a new queue manager, a new queue manager configuration file (qm.ini) is automatically created. This contains configuration parameters for the queue manager.

After creating a queue manager, we recommend that you back up your configuration files.

If, later on, you create another queue manager that causes you problems, you can reinstate the backups when you have removed the source of the problem. As a general rule, back up your configuration files each time you create a new queue manager.

For more information about configuration files, see Chapter 9, "Configuring WebSphere MQ".