HP OpenVMS Systems

MONITOR Display Inconsistencies?

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The Question is:

 
Using Monitor, I've seen as many as nine processes in "CUR" state at one time.
 How is this possible when the node only has six CPU's?
 

The Answer is :

 
  MONITOR does a sequential scan of the process list; it does not take an
  instantaneous snapshot and it does not take out a lock on the data
  structures.  On a very busy system, it is quite possible that the state
  of previously scanned processes has changed by the time MONITOR gets to
  the end of the list -- a previously scanned process has changed from CUR
  to COM, and a yet-to-be scanned process has changed from COM to CUR by
  the time MONITOR gets to it, for instance.   MONITOR displays the result
  of the entire scan when it has completed the pass.  The process state
  displayed by MONITOR is thus the individual state of each process from
  the recent past, and is not a snapshot of the aggregate state of all
  processes.
 
  Also do not forget that MONITOR itself is running in a process, and is
  subject to being pre-empted by other processes. So the MONITOR process
  scan can take a relatively long time, which also contributes to the
  behavior you are seeing.  You can also see odd data resulting from
  processes performing periodic work and MONITOR -- values for activity
  can be unusual, depending on the particulars of the process activity
  and the MONITOR sampling interval.
 

  

     

     
answer written or last revised on ( 23-MAY-2000 )
     
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