ENQ/RESERVE/DEQ restrictions

The ENQ/DEQ/RESERVE monitor has some restrictions:
  • The ENQ RET=TEST requests are traced, but they are discarded during data reduction.
  • The maximum length of the minor name traced is 52 bytes (data set name length plus member name). The reported minor name length can be used to see if the minor name has been truncated.
  • Data is collected at the entry of the SVC. If RNLs are active, GRS simulates data collection.
  • GRS traces only the first parameter list entry for RESERVE requests.
  • The maximum RESERVE time measurable is around 4 hours 45 minutes, the lowest reserve time is rounded to 1 millisecond.
  • If you specify the same RESERVE resource name (major and minor) for different volumes, GRS reports incorrect data.
  • If GRS discards RESERVE requests with the filter, the timings given in the volume-reserve-time procedure are incorrect.
  • If a job is cancelled or ABENDs with an active RESERVE, the timings given in the volume-reserve-time procedure are incorrect.
  • The maximum ENQ delay-time measurable is 99.99 seconds.
  • GRS registers the RESERVE count before issuing the hardware reserve. Therefore for volumes with high contention, the count might be incorrect along with the measured reserve time.
  • If you issue DEQ requests without an outstanding reserve, the measured reserve time might be incorrect. Likely candidates include CATALOG address space and HSM subsystem.
  • In a global resource serialization complex, only the ENQ/DEQ issued in the system where the monitor is active are traced.
  • The monitor encounters the same contention for the processor and storage as does any other address space in the system. Thus, even after the system grants the global resource request, the monitor might not receive control immediately because of processor or storage contention, and the ENQ delay measurement might not be accurate. Experience shows that the tool can lose data if the global resource serialization ENQ delay exceeds 500 msec. or more.
  • The NUMSYS (number of systems in the global resource serialization complex) value is updated periodically through an internal command or when you enter a Modify command.