Using the DL/I-Call-Summary report

The primary usefulness of the DL/I-Call-Summary report is to track down DL/I calls that are causing a large number of IWAITs.

If the number in the IWAITS/CALL field is relatively high, you want to know why. Because the number in the report is related to a specific DL/I call, segment, and PCB, you can trace the IWAITs back to a specific part of an application program. In addition, by using the Distribution-Appendix report, you can see how many of the DL/I calls being issued are distorting the average in the IWAITS/CALL field. See Distribution-Appendix report for additional ways in which information from the DL/I-Call-Summary report can be used.

Remember, in tuning to decrease I/O operations, pay most attention to calls issued a large number of times. It is more profitable to save 1 second on a call executed 2000 times than to save 5 seconds on a call executed ten times (2000 versus 50 seconds).