Performance problems

This information provides documentation requirements and diagnosis procedures for performance problems. Use this information along with the information in Performance problem. In addition to the documentation required in Performance problem, you will need a GTF trace of SVC 93 and SVC 94 entries. See Table 1 to determine what document describes the SVC 93 and SVC 94 entries.

1. Are wait and hold options slowing response time?

   The application program may be issuing TPUTs and TGETs with the wait or hold options. The wait option indicates that the application program should not regain control until output data has been placed on the output queue (TPUT) or input is available (TGET). A TPUT with a hold option indicates that control should not be returned to the application until the data has reached the terminal. These options may be necessary for screen management, but they prolong response time and increase the number of times the address space is swapped.

2. Is an external system resource slowing response time?

   If all users must access the same resource, such as a system catalog, performance deteriorates. This problem is especially severe when exclusive ENQs are used to control access to the resource. To improve performance, redistribute resources.

3. Are high and low buffer extents set at inappropriate values?

   If the high and low buffer extents are too close together, output wait states occur.Buffer extents are specified in TSOKEY00, a member of SYS1.PARMLIB. Tune the values of the high and low buffer extents to get optimum performance.

4. Are APPL definition statements coded correctly?

   Code the AUTH=NVPACE operand on all APPL definition statements for TSO/VTAM.

   If you do not set NVPACE, VTAM® indicates that it has already received input data, instead of queuing the response until it receives the input data. Also, the swap count is incremented by two every time the ENTER key is pressed.

5. Are pacing values set correctly for local SNA terminals?

   VTAM ignores the NVPACE operand for sessions with logical units in a local major node. Therefore, you must set nonzero pacing values for these logical units.

6. Is the MVS™ performance group specified correctly?

   Set the application program's performance group approximately five to ten percent lower than the VTAM performance group. To see the application program's performance group specification, look at the dispatching priority in the task's TCB.

7. If you have not resolved the performance problem, go to Performance problem.