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Rule: Define

Defined rules allow the creation of a derived metric. A defined metric is useful to calculate information based off of gathered data and expose it to the processor (for example, grapher cannot (easily) declare a metric expression, so by declaring it here you can make the derivation show up as any other metric).

Syntax

define group_name [ tag ( tag_name = tag_expr [, ...] ) ] metric = expression ;

  • group_name The name of a group. The metric will be created inside this group. If the group doesn't exist, it will be created.
  • tag_name Add an additional tag to the defined metrics.
  • tag_expr An expression to resolve as the value of the tag.
  • metric The metric name in the group under which to expose the expression. If the group already holds a metric under this name, it will be replaced.
  • expression An expression that yields a value for the metric.

Example

define com.groupon.brands.requesthandlers.CountryBrandsFuzzySearchHandler qps =
  rate(com.groupon.brands.requesthandlers.CountryBrandsFuzzySearchHandler Count);

Define a qps rate, based on a monotonic incrementing counter. The resulting metric will be exposed as com.groupon.brands.requesthandlers.CountryBrandsFuzzySearchHandler qps.

match com.groupon.brands.requesthandlers.* as handler {
  define ${handler} qps = rate(handler Count);
}

Define a qps rate for all endpoints, based on a monotonic incrementing counter. Note that the left-hand-side of the expression uses the name resolution, while the right-hand-side of the expression uses the normal resolution. The resulting metric will be exposed on the same group, with the name qps.