Method R and CPU Time

From: MacGregor, Ian A. <ian_at_slac.stanford.edu>
Date: Thu, 1 Jul 2004 13:42:00 -0700
Message-ID: <26E3EC48949D134C94A1574B2C89466113A95E@exchange2.slac.stanford.edu>

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_at_slac.stanford.edu

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Received on Thu Jul 01 2004 - 15:39:14 CDT