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MainView for z/OS
MainView for z/OS
How do I increase the duration of a MVScope trace?
With MVScope, sampling ends at the first point where the combination of three parameters (MXDUR/MXSAM/SAMRAT) indicate that the sampling conditions have been met. Changing one without balancing the change with the settings of the other two may not produce the desired results.
The parameters are documented as follows (see the MainView for z/OS User Guide and Reference Manual for further details)
- MXDUR maximum number of seconds that sample occurs (default value: 60, value range: 1 to 9999)
- MXSAM maximum number of CPU samples to be taken (default value: 600, value range: 1 to 99999)
- SAMRAT number of CPU samples per second (default value: 10, value range: 1 to 999)
The default values are used unless the user defines a BBDTMSDP PARMLIB member in the UBBPARM data set. This PARMLIB member allows you to specify and define default sampling parameters, which will be used for all monitoring sessions. MVScope uses the distributed default value for sampling parameters when BBDTMSDP is not defined in the PARMLIB.
Sampling stops at whatever limit is reached first irrespective of what may be coded in the other parameters.
Suppose that the following parameters are coded:-
SAMRAT = 20.
MXSAM = 800
MAXDUR = 60
Dividing MXSAM (800) by SAMRAT (20) gives 40. Therefore, in this case, sampling will stop after 40 seconds, even though MXDUR was coded as 60 seconds. If a user wishes to increase the MXDUR parameter, MXSAM should also be increased (or SAMRAT decreased) so that the MXDUR multiplied by SAMRAT is less than or equal to MXSAM.
If a user wanted to increase the duration of a MVSCOPE trace from 60 to 120 seconds, then MXSAM could be set to 2400. If SAMRAT had been set to 20, then 2400 samples divided by 20 samples per second gives a result of 120 seconds
1) MAXDUR is the maximum duration (in seconds), not the absolute sampling duration.
2) MXSAM is not the number of samples collected for the job being monitored, but is the number of times the monitoring routine is invoked, even if the monitored address space is not running at the time.