What is a queue manager?

A queue manager is a system program that provides queuing services to applications. It provides an application programming interface so that programs can put messages on, and get messages from, queues. A queue manager provides additional functions so that administrators can create new queues, alter the properties of existing queues, and control the operation of the queue manager.

For WebSphere MQ message queuing services to be available on a system, there must be a queue manager running:

• On OS/400^(R), z/OS, OS/2, Windows systems, Compaq OpenVMS Alpha, and UNIX systems, you can have more than one queue manager running on a single system (for example, to separate a test system from a "live" system). To an application, each queue manager is identified by a connection handle (Hconn).
• On the VSE/ESA platform you can have only one queue manager running on a single system. Hconn is still used, but only to give compatibility with other WebSphere MQ platforms.

Many different applications can make use of the queue manager's services at the same time and these applications can be entirely unrelated. For a program to use the services of a queue manager, it must establish a connection to that queue manager.

For applications to be able to send messages to applications that are connected to other queue managers, the queue managers must be able to communicate among themselves. WebSphere MQ implements a store-and-forward protocol to ensure the safe delivery of messages between such applications.