IBM MQ message handling

Conceptually, the IBM MQ message handling system takes a piece of information (the message) and sends it to its destination. MQ guarantees delivery, despite any network disruptions that might occur.

In IBM MQ, a destination is called a message queue, and a queue resides in a queue manager. Applications can put messages on queues or get messages from them.

Db2 communicates with the WebSphere® message handling system through a set of external user-defined functions, which are called Db2 MQ functions. These functions use the MQI.

When you send a message, you must specify the following three components:
message data
Defines what is sent from one program to another.
service
Defines where the message is going to or coming from. The parameters for managing a queue are defined in the service, which is typically defined by a system administrator. The complexity of the parameters in the service is hidden from the application program.
policy
Defines how the message is handled. Policies control such items as:
  • The attributes of the message, for example, the priority.
  • Options for send and receive operations, for example, whether an operation is part of a unit of work.

The default service and policy are set as part of defining the WebSphere MQ configuration for a particular installation of Db2. (This action is typically performed by a system administrator.) Db2 provides the default service Db2.DEFAULT.SERVICE and the default policy Db2.DEFAULT.POLICY.