Add docs for cacheRules

README.md

@@ -44,6 +44,7 @@ lowercaseOutputName: false
 lowercaseOutputLabelNames: false
 whitelistObjectNames: ["org.apache.cassandra.metrics:*"]
 blacklistObjectNames: ["org.apache.cassandra.metrics:type=ColumnFamily,*"]
+cacheRules: true
 rules:
   - pattern: 'org.apache.cassandra.metrics<type=(\w+), name=(\w+)><>Value: (\d+)'
     name: cassandra_$1_$2
@@ -68,6 +69,7 @@ lowercaseOutputLabelNames | Lowercase the output metric label names. Applies to
 whitelistObjectNames | A list of [ObjectNames](http://docs.oracle.com/javase/6/docs/api/javax/management/ObjectName.html) to query. Defaults to all mBeans.
 blacklistObjectNames | A list of [ObjectNames](http://docs.oracle.com/javase/6/docs/api/javax/management/ObjectName.html) to not query. Takes precedence over `whitelistObjectNames`. Defaults to none.
 rules      | A list of rules to apply in order, processing stops at the first matching rule. Attributes that aren't matched aren't collected. If not specified, defaults to collecting everything in the default format.
+cacheRules | Enables caching of regular expression matching in rules. Enabling this feature [may reduce CPU usage and improve performance](https://engineeringblog.yelp.com/2020/10/improving-the-performance-of-the-prometheus-jmx-exporter.html). Defaults to false.
 pattern           | Regex pattern to match against each bean attribute. The pattern is not anchored. Capture groups can be used in other options. Defaults to matching everything.
 attrNameSnakeCase | Converts the attribute name to snake case. This is seen in the names matched by the pattern and the default format. For example, anAttrName to an\_attr\_name. Defaults to false.
 name              | The metric name to set. Capture groups from the `pattern` can be used. If not specified, the default format will be used. If it evaluates to empty, processing of this attribute stops with no output.

example_configs/kafka-2_0_0.yml

@@ -1,5 +1,5 @@
 lowercaseOutputName: true
-
+cacheRules: true
 rules:
 # Special cases and very specific rules
 - pattern : kafka.server<type=(.+), name=(.+), clientId=(.+), topic=(.+), partition=(.*)><>Value