Re: Method R and CPU Time

  • From: Daniel Fink <Daniel.Fink@xxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Thu, 01 Jul 2004 14:59:57 -0600

Ian,

I know this does not answer your question, but the fact that each event had the 
*exact* same CPU_SECs strikes me as odd. Are you sure this 
calculation/retrieval is correct?

As for CPU_SECS + WAIT_SECS = ELA_SECS, CPU is only incremented when the 
process is on the CPU and the CPU clock increments. It is theoretically 
possible that you could accumulate 0 cpu_seconds because the process was never 
on the CPU when the clock ticked. You could also have CPU seconds in the PARSE, 
EXEC
and FETCH calls that may not be accounted for here.

Regards,
Daniel Fink

"MacGregor, Ian A." wrote:

> I'm having a hard time determining how much time is actually spent on CPU,
>
> Consider the following
> Runtime           TRACE_ID        EVENT                               WAITS  
> WAIT_SECS ELAPSED_SECS   CPU_SECS
> 25-JUN-2004 12:05 nlco_ora_7279   db file sequential read                96   
>      .27        14.29      13.07
> 25-JUN-2004 12:05                 db file scattered read                378   
>     7.14        14.29      13.07
> 25-JUN-2004 12:05                 SQL*Net message from client           475   
>     1.34        14.29      13.07
>                                   ***************************           ----- 
>    -----
>                                   sum                                   949   
>     8.75
>
> The CPU_SECS + WAIT_SECS should equal elapsed secs at least approximately.  I 
> know there is some double counting between the file i/o waits and the CPU's  
> but 13.07 + 8.75 = 21.82 and 21.82/14.29 * 100 = anout 153%.  That's a lot 
> more than the incidental double-counting error Cary speaks of in his book.
>
> This particular machine has 4 CPU's and when looking at CPU usage at the 
> system level one needs to take that into account.  But what about for 
> individual statements that are not parallelized; i.e., running against one 
> and only one CPU, does one need to divide  the CPU results by four on a four 
> CPU machine.
>
> Ian MacGregor
> Stanford Linear Accelerator Center
> iam@xxxxxxxxxxxxxxxxx
>
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