Oracle Scratchpad

June 9, 2019

CPU percent

Filed under: 12c,AWR,Oracle — Jonathan Lewis @ 2:31 pm BST Jun 9,2019

A recent post on the ODC General Database forum asked for an explanation of the AWR report values “%Total CPU” and “%Busy CPU” under the “Instance CPU” label, and how the “%Busy CPU “ could be greater than 100%.  Here’s a text reproduction of the relevant sample supplied:

Host CPU

CPUs Cores Sockets Load Average Begin Load Average End %User %System %WIO %Idle
2 2 1 0.30 1.23 10.7 5.6 5.3 77.7

Instance CPU

%Total CPU %Busy CPU %DB Time waiting for CPU (Resource Manager)
29.8 133.8 0.0

The answer is probably “It’s 12.1 and it’s a programmer error”.

  • Note that the Host CPU %Idle is not consistent with the three usage figures:  10.7 + 5.6 + 5.3 = 21.6 whereas 100 – 77.7 = 22.3.
  • So let’s run with 22.3% and see what else we can notice: 29.8 / 22.3 = 1.3363 – that’s pretty close (when expressed as a percentage) to 133.8%

Hypothesis:

Someone did the division the wrong way round when trying to work out the percentage of the host’s non-idle CPU that could be attributed to the instance. In this example the “%Busy CPU” should actually report 100 * 22.3 / 29.8 = 74.8%

Note – the difference between 133.8 and 133.63 can be attributed to the fact that the various figures reported in this bit of the AWR are rounded to the nearest 1 decimal place.

Note 2 – I don’t think this error is present in 11.2.0.4 or 12.2.0.1

 

 

 

 

 

2 Comments »

  1. There are many problems with AWR reports in 12.1
    For instance, AWR reports do not work properly with PDBs in 12.1 or 12.2, as a number metrics are missing.
    AWR does appear to work properly in 19c PDBs. I have not tested 18c.

    Comment by jkstill — June 9, 2019 @ 4:12 pm BST Jun 9,2019 | Reply

  2. If we’re “trying to work out the percentage of the host’s non-idle CPU that could be attributed to the instance”, it makes sense to divide the instance CPU / host non-idle, so arguably the division done is the right way – what’s weird is that “% total cpu” of the instance is higher than that of the host…

    Comment by Nickolay — June 10, 2019 @ 12:44 pm BST Jun 10,2019 | Reply


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