IBM WebSphere MQ messages

This information introduces the IBM® WebSphere® MQ message concept, message parts, and the message descriptor.

IBM WebSphere MQ messages consist of two parts:
  • Message properties
  • Application data
Figure 1 represents a message and shows how it is logically divided into message properties and application data.
Figure 1. Representation of a message
A message made up of: Message Descriptor which in turn is made up of Message ID and Persistence. These form message properties. The Application Data portion of the message contains two fields: Address and Claim Details.

The application data carried in a WebSphere MQ message is not changed by a queue manager unless data conversion is carried out on it. Also, WebSphere MQ does not put any restrictions on the content of this data. The length of the data in each message cannot exceed the value of the MaxMsgLength attribute of both the queue and queue manager.

On WebSphere MQ for AIX®, WebSphere MQ for HP-UX, WebSphere MQ for Linux®, WebSphere MQ for Solaris, and WebSphere MQ for Windows, the MaxMsgLength defaults to 100 MB (104 857 600 bytes).

Make your messages slightly shorter than the value of the MaxMsgLength attribute in some circumstances. See The data in your message for more information.

You create a message when you use the MQPUT or MQPUT1 MQI calls. As input to these calls, you supply the control information (such as the priority of the message and the name of a reply queue) and your data, and the call then puts the message on a queue. See MQPUT and MQPUT1 for more information about these calls.

Message descriptor
You can access message control information using the MQMD structure, which defines the message descriptor.

For a full description of the MQMD structure, see MQMD - Message descriptor.

See Message context for a description of how to use the fields within the MQMD that contain information about the origin of the message.

There are different versions of the message descriptor. Additional information for grouping and segmenting messages (see Message groups) is provided in Version 2 of the message descriptor (or the MQMDE). This is the same as the Version 1 message descriptor but has additional fields. These are described in the MQMDE - Message descriptor extension.