atris commented on a change in pull request #1737:
URL: https://github.com/apache/lucene-solr/pull/1737#discussion_r471291807
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File path: solr/solr-ref-guide/src/circuit-breakers.adoc
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@@ -35,33 +35,67 @@ will be disabled globally. Per circuit breaker
configurations are specified in t
<useCircuitBreakers>false</useCircuitBreakers>
----
+This flag acts as the highest authority and global controller of circuit
breakers. For using specific circuit breakers, each one
+needs to be individually enabled in addition to this flag being enabled.
+
== Currently Supported Circuit Breakers
=== JVM Heap Usage Based Circuit Breaker
This circuit breaker tracks JVM heap memory usage and rejects incoming search
requests with a 503 error code if the heap usage
exceeds a configured percentage of maximum heap allocated to the JVM (-Xmx).
The main configuration for this circuit breaker is
controlling the threshold percentage at which the breaker will trip.
-It does not logically make sense to have a threshold below 50% and above 95%
of the max heap allocated to the JVM. Hence, the range
-of valid values for this parameter is [50, 95], both inclusive.
+To enable/disable JVM heap usage based circuit breaker, use the following
configuration:
+
+[source,xml]
+----
+<isMemoryCircuitBreakerEnabled>true</isMemoryCircuitBreakerEnabled>
+----
+
+Note that this configuration will be overridden by the global circuit breaker
flag -- if circuit breakers are disabled, this flag
+will not help you.
+
+To set the triggering threshold as a percentage of the max heap allocated to
the JVM, use the following parameter.
[source,xml]
----
<memoryCircuitBreakerThresholdPct>75</memoryCircuitBreakerThresholdPct>
----
+It does not logically make sense to have a threshold below 50% and above 95%
of the max heap allocated to the JVM. Hence, the range
+of valid values for this parameter is [50, 95], both inclusive.
Consider the following example:
JVM has been allocated a maximum heap of 5GB (-Xmx) and
memoryCircuitBreakerThresholdPct is set to 75. In this scenario, the heap usage
at which the circuit breaker will trip is 3.75GB.
-Note that this circuit breaker is checked for each incoming search request and
considers the current heap usage of the node, i.e every search
-request will get the live heap usage and compare it against the set memory
threshold. The check does not impact performance,
-but any performance regressions that are suspected to be caused by this
feature should be reported to the dev list.
+=== CPU Utilization Based Circuit Breaker
+This circuit breaker tracks CPU utilization and triggers if the average CPU
utilization over the last minute
+exceeds a configurable threshold.
+
+To enable/disable CPU utilization based circuit breaker, use the following
configuration:
+
+[source,xml]
+----
+<isCpuCircuitBreakerEnabled>true</isCpuCircuitBreakerEnabled>
+----
+
+Note that this configuration will be overridden by the global circuit breaker
flag -- if circuit breakers are disabled, this flag
+will not help you.
+
+To set the triggering threshold in units of CPU utilization, use the following
parameter.
+[source,xml]
+----
+<cpuCircuitBreakerThreshold>75</cpuCircuitBreakerThreshold>
+----
+The range of valid values for this parameter is [40 to infinity].
Review comment:
Removed.
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