Sample Programs and Database Definition › CA IDMS/DC Programming Considerations

CA IDMS/DC Programming Considerations

These programming considerations consist of PL/I-specific details relevant to designing CA IDMS/DC programs:

• Reentrant code is program code that does not modify itself during program execution. CA IDMS/DC multithreads all task requests through a single copy of a reentrant program. The CA IDMS/DC default for PL/I programs is reentrant. To ensure that your program is reentrant, it must be compiled with the REENTRANT option of the PROCEDURE statement. Some PL/I compilers do not support reentrancy. If your compiler does not support reentrancy, your programs must be declared to CA IDMS/DC as NONREENTRANT.
• Use the COUNT and REPORT execution options to capture statistics in the CA IDMS/DC log. You can use these statistics to optimize storage requirements and to analyze program performance.
• Avoid using GET STORAGE repeatedly for relatively small areas when most tasks in the system are accessing larger areas. It may be more advantageous to declare PL/I variables explicitly and allow CA IDMS/DC and PL/I to manage the storage. Internal management of storage for PL/I declared variables is handled in the same way under IDMS/DC as it is in the batch environment, with one exception. When PL/I code would normally issue an operating system request for storage, CA IDMS/DC satisfies the request from the storage pool. Once a block of storage is allocated, it is managed as described in the PL/I programmer's guide for your installation.
• Use the REPORT execution option to determine the amount of storage actually used during program execution. Use the report statistics to set the ISA SIZE for the program in the CA IDMS/DC system generation.
• The PL/I COUNT and FLOW options can be used to gather the following statistics:
  • The number of times each procedure is called
  • The amount of storage used during PL/I program execution.

  To use these options, refer to the PL/I programmer's guide for your installation. The following considerations apply to the use of these options under CA IDMS/DC:

  • The statistics are written to the CA IDMS/DC system log rather than to an external file. The statistics record type is MESSAGES.
  • The statistics are not written to the log if the program terminates execution with an IDMS_DC RETURN statement. The program must use the PL/I RETURN statement. After statistics are written to the log, CA IDMS/DC passes control to the next higher program in the transaction thread, as if an CA IDMS/DC RETURN had been coded.
  • The REPORT and COUNT options should not be used together, since the COUNT option adds storage overhead. Accordingly, report statistics would not be accurate.
  • The REPORT and COUNT options are not intended to be used in a production environment. Their use adds considerable storage and CPU overhead under CA IDMS/DC, just as it would in a batch environment. Once the statistics have been gathered, these options should be removed from the program.