Grouping logical messages

There are two main reasons for using logical messages in a group:

• You might need to process the messages in a particular order.
• You might need to process each message in a group in a related way.

In either case, retrieve the entire group with the same getting application instance.

For example, assume that the group consists of four logical messages. The putting application looks like this:

   PMO.Options = MQPMO_LOGICAL_ORDER | MQPMO_SYNCPOINT

   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP
   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP
   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP
   MQPUT MD.MsgFlags = MQMF_LAST_MSG_IN_GROUP

   MQCMIT

The getting application specifies the MQGMO_ALL_MSGS_AVAILABLE option for the first message in the group. This ensures that processing does not start until all the messages within the group have arrived. The MQGMO_ALL_MSGS_AVAILABLE option is ignored for subsequent messages within the group.

When the first logical message of the group is retrieved, we can use MQGMO_LOGICAL_ORDER to ensure that the remaining logical messages of the group are retrieved in order.

So, the getting application looks like this:

   /* Wait for the first message in a group, or a message not in a group */
   GMO.Options = MQGMO_SYNCPOINT | MQGMO_WAIT
               | MQGMO_ALL_MSGS_AVAILABLE | MQGMO_LOGICAL_ORDER
   do while ( GroupStatus == MQGS_MSG_IN_GROUP )
      MQGET
      /* Process each remaining message in the group */
      ...

   MQCMIT

For further examples of grouping messages, see Application segmentation of logical messages and Putting and getting a group that spans units of work.

For information on allowing an application to request that a group of messages are all allocated to the same destination instance for cluster queues, see DefBind.