4 Replies Latest reply on Jun 9, 2019 9:17 PM by 2729747

    Meaning of "%Total CPU" and "%Busy CPU" in AWR

    2729747

      Hi guys,

       

      Following is an excerpt from an AWR  report.

       

      My questions are:

      (1) What is the "%Total CPU" under  the Instance CPU?

      Obviously it isn't how much CPU is consumed by the instance because the "%User" is 10.7% and there is no way for the Instance CPU consumption to be more than %User.

       

      (2) What is the "%Busy CPU"? How come it is more than 100?

       

       

      Host CPU

       

      CPUsCoresSocketsLoad Average BeginLoad Average End%User%System%WIO%Idle
      2210.301.2310.75.65.377.7

       

      Instance CPU

       

      %Total CPU%Busy CPU%DB time waiting for CPU (Resource Manager)
      29.8133.80.0

       

       

       

      It's Oracle 12c R2 on Linux x86-64.

        • 1. Re: Meaning of "%Total CPU" and "%Busy CPU" in AWR
          Jonathan Lewis

          Unfortunately the numbers look almost self-consistent - provided you assume a programmer made silly mistake:

           

          • "non-idle" CPU is (100 - 77.7)% = 22.3%  (Note that the sum of the 3 non-idle CPU values is NOT 22.3%)
          • 29.8 / 22.3 = 1.3363

           

          It looks to me as if the 1.3363 is supposed to be the percentage of the total non-idle CPU that has been used by your instance - but the programmer has got the division upside down. For an intuitive understanding the number should have been 22.3 / 29.8 = 74.8%.

           

           

          (I think the difference between 1.3362 and 1.338 can be explained by the fact that the aritimetic being done to far more decimal places than the 1 d.p. shown for the Host CPU reports.)

           

          Regards

          Jonathan Lewis

          • 2. Re: Meaning of "%Total CPU" and "%Busy CPU" in AWR
            Franck Pachot

            Hi,

            Can you show the time model statistics ('DB CPU' and 'background cpu time') and Operating System Statistics (BUSY_TIME, IDLE_TIME and NUM_CPUS) from the same report? And the elapsed time of the report

            I think the formulas are something like:

              %Total CPU = (instance CPU from Time Model) / (num cpu * elapsed time)

              %Busy CPU = (instance CPU from Time Model) / (OS non-idle time)

            Thanks,

            Franck.

            • 3. Re: Meaning of "%Total CPU" and "%Busy CPU" in AWR
              Jonathan Lewis

              Franck Pachot wrote:


              I think the formulas are something like:

              %Total CPU = (instance CPU from Time Model) / (num cpu * elapsed time)

              %Busy CPU = (instance CPU from Time Model) / (OS non-idle time)

              What it should be and what it seems to be can be two very different things.

              I'm looking at a few AWR reports from a 12.1 system where

               

              %Total CPU seems to be ("Total CPU time" from Time Model Statistics) / ("BUSY_TIME" + "IDLE_TIME" from Operating System Statistics)

              and

              %Busy CPU = ("Total CPU time" from Time Model Statistics) / "BUSY_TIME" from Operating System Statistics)

               

              However, the Total CPU time is roughly 40%  greater than the BUSY_TIME (22,380 seconds vs. 15,893 seconds)! so the %Busy CPU is (quite correctly, for some value of "correct")  140.8%)

               

              Picking just one report, though, I can see BUSY_TIME  + IDLE_TIME = 106,398, while elapsed time * CPU count = 114,416 so there's more than 8,000 seconds "lost" time.  (Naturally the confusion is compounded by the fact that it's 8 cores and 16 CPUs).

               

              Regards

              Jonathan Lewis

              • 4. Re: Meaning of "%Total CPU" and "%Busy CPU" in AWR
                2729747

                Elapsed time:

                Snap IdSnap TimeSessionsCursors/Session
                Begin Snap:88806-Jun-19 22:30:1156.9
                End Snap:88906-Jun-19 23:00:1454.9
                Elapsed:30.05 (mins)
                DB Time:27.36 (mins)

                 

                 

                Time Model Statistics

                Statistic NameTime (s)% of DB Time% of Total CPU Time
                DB CPU778.0347.3984.42
                sql execute elapsed time667.4140.66
                PL/SQL execution elapsed time264.2316.10
                parse time elapsed10.950.67
                repeated bind elapsed time0.460.03
                hard parse elapsed time0.140.01
                connection management call elapsed time0.070.00
                PL/SQL compilation elapsed time0.030.00
                sequence load elapsed time0.000.00
                DB time1,641.63
                background elapsed time950.95
                background cpu time143.5915.58
                total CPU time921.62

                 

                Operating System Statistics

                StatisticValueEnd Value
                FREE_MEMORY_BYTES39,464,96041,435,136
                INACTIVE_MEMORY_BYTES1,314,881,5361,247,432,704
                SWAP_FREE_BYTES5,960,953,8565,921,521,664
                BUSY_TIME68,905
                IDLE_TIME240,014
                IOWAIT_TIME16,408
                NICE_TIME0
                SYS_TIME17,172
                USER_TIME32,987

                 

                 

                My observations:

                DB CPU (778 seconds) is longer than the BUSY_TIME (68905/100= 689.05 seconds) which doesn't make sense

                 

                Jonathan proposed formulas applied in my report.