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%


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 or







  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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