SHMSGSZ= parameter for procedures
Use the SHMSGSZ= parameter in procedure to specify a 1- to 5-digit number that represents the length in bytes of a short message record.
The length of the short message record cannot exceed 30632 bytes. The length must also be greater than or equal to the number of bytes in one and one-half times the maximum message prefix length plus 4. If you specify a smaller value, the message size is set to the greater value between the size in the DCB LRECL and one and one-half times the maximum message prefix size plus 4. If you specify a value greater than 30632, the size is set to 30632. If the specified value is usable, it is rounded up to the nearest multiple of 4.
This parameter is only valid in the shared-queues environment. If you specify a value for SHAREDQ=, but not for SHMSGSZ=, the size of the short message record is obtained from the DCB generated for the short message queue data set. The DCBs for the message queue data sets are built during the IMS system generation process even though the data sets are not used.
Choose values for the SHMSGSZ= and the LGMSGSZ= based on the sizes of the messages that are processed by the queue manager. When determining which size message queue record to use, the queue manager calculates the size of the message prefix, subtracts that value from the size of the short message queue buffer and then doubles the remaining value. It then compares that value to the average user data length for the destination. If the remainder buffer size is greater than or equal to the average user data size, then the short message queue buffer is used. If the remainder buffer size is less than the average user data size, then the large message queue buffer is used. The length of the message prefix varies based on the IMS system options specified.