Walter Underwood created SOLR-15056:
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Summary: CPU circuit breaker needs to use CPU utilization, not
Unix load average
Key: SOLR-15056
URL: https://issues.apache.org/jira/browse/SOLR-15056
Project: Solr
Issue Type: Bug
Security Level: Public (Default Security Level. Issues are Public)
Components: metrics
Affects Versions: 8.7
Reporter: Walter Underwood
The config range, 50% to 95%, assumes that the circuit breaker is triggered by
a CPU utilization metric that goes from 0% to 100%. But the code uses the
metric OperatingSystemMXBean.getSystemLoadAverage(). That is an average of the
count of processes waiting to run. It is effectively unbounded. I've seen it as
high as 50 to 100. It is not bound by 1.0 (100%).
A good limit for load average would need to be aware of the number of CPUs
available to the JVM. A load average of 8 is no problem for a 32 CPU host. It
is a critical situation for a 2 CPU host.
Also, load average is a Unix OS metric. I don't know if it is even available on
Windows.
Instead, use a CPU utilization metric that goes from 0.0 to 1.0. A good choice
is OperatingSystemMXBean.getSystemCPULoad(). This name also uses "load", but it
is a usage metric.
>From the Javadoc:
> Returns the "recent cpu usage" for the whole system. This value is a double
>in the [0.0,1.0] interval. A value of 0.0 means that all CPUs were idle during
>the recent period of time observed, while a value of 1.0 means that all CPUs
>were actively running 100% of the time during the recent period being
>observed. All values betweens 0.0 and 1.0 are possible depending of the
>activities going on in the system. If the system recent cpu usage is not
>available, the method returns a negative value.
https://docs.oracle.com/javase/7/docs/jre/api/management/extension/com/sun/management/OperatingSystemMXBean.html#getSystemCpuLoad()
Also update the documentation to explain which JMX metrics are used for the
memory and CPU circuit breakers.
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