PIU Buffer Allocation and Tuning
Define trace buffers using the NLDM.PIUTNUM and NLDM.PIUTSIZE statements in the CNMSTUSR or CxxSTGEN member.
The DSIAMLUT task receives the PIU buffers from VTAM® and forwards them to the AAUTSKLP task for processing. The storage for PIU buffers is common storage page fixed. If VTAM does not have enough trace buffers and starts overlaying them, the NetView® program issues message AAU024I indicating the number of lost buffers. Losing PIU buffers is usually not a problem unless you are using the session monitor accounting function or are not getting the desired trace data.
- Maximize the number of PIUs that are sent per buffer.
- Avoid losing PIU buffers.
- Avoid over allocating buffers, which wastes storage.
VTAM sends full PIU buffers unless the NetView program solicits a buffer, as it might when processing a session-end notification or when processing an operator request. Therefore, the optimum PIU buffer allocation depends on the rate at which session-end notifications are processed and the frequency of operator requests for PIU trace data.
In tuning the PIU buffer allocation, determine the optimum size of the buffers for your environment. Then adjust the number of buffers to allocate so that PIU buffers are not lost during periods of peak activity.
The SESSMDIS command and the external log record created by the NLDM RECORD STRGDATA command provide information that you can use to tune the PIU buffer allocation for your system. The SESSMDIS command displays session monitor traffic data and event counters, while the NLDM RECORD STRGDATA command writes similar information to the NetView external log. The NLDM RECORD STRGDATA command creates SMF record type 39, subvector X'0008'. See the IBM® Tivoli® NetView for z/OS® Command Reference Volume 1 (A-N) or the NetView online help for information about the syntax and use of those commands. See the IBM Tivoli NetView for z/OS Application Programmer's Guide for the format of the external log record.