Application segmentation of logical messages

 

The messages must be maintained in logical order in a group, and some or all of them might be so large that they require application segmentation.

In our example, a group of four logical messages is to be put. All but the third message are large, and require segmentation, which is performed by the putting application:

   PMO.Options = MQPMO_LOGICAL_ORDER | MQPMO_SYNCPOINT

   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP      | MQMF_SEGMENT
   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP      | MQMF_SEGMENT
   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP      | MQMF_LAST_SEGMENT

   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP      | MQMF_SEGMENT
   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP      | MQMF_LAST_SEGMENT

   MQPUT MD.MsgFlags = MQMF_MSG_IN_GROUP

   MQPUT MD.MsgFlags = MQMF_LAST_MSG_IN_GROUP | MQMF_SEGMENT
   MQPUT MD.MsgFlags = MQMF_LAST_MSG_IN_GROUP | MQMF_SEGMENT
   MQPUT MD.MsgFlags = MQMF_LAST_MSG_IN_GROUP | MQMF_LAST_SEGMENT

   MQCMIT

In the getting application, MQGMO_ALL_MSGS_AVAILABLE is specified on the first MQGET. This means that no messages or segments of a group are retrieved until the entire group is available. When the first physical message of a group has been retrieved, MQGMO_LOGICAL_ORDER is used to ensure that the segments and messages of the group are retrieved in order:

   GMO.Options = MQGMO_SYNCPOINT | MQGMO_LOGICAL_ORDER
               | MQGMO_ALL_MESSAGES_AVAILABLE | MQGMO_WAIT

   do while ( (GroupStatus   != MQGS_LAST_MSG_IN_GROUP) ||
                 (SegmentStatus != MQGS_LAST_SEGMENT) )
      MQGET
      /* Process a segment or complete logical message.  Use the GroupStatus
         and SegmentStatus information to see what has been returned */
      ...

   MQCMIT

If you specify MQGMO_LOGICAL_ORDER and there is a current group, MQGMO_ALL_MSGS_AVAILABLE is ignored.

 

Parent topic:

Message segmentation

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