Ruby custom metrics

Custom metrics let you record arbitrary performance data via an API call (for example, timing or computer resource data). Then use the query builder to create charts and track that metric. You can use custom metrics to unify your monitoring inside New Relic.

Naming metrics

Metric names identify specific data values tracked by New Relic. When using the New Relic Ruby agent's API to track custom metrics, it's important to consider your metric naming and how the values will aggregate.

A custom metric name consists of the prefix Custom/, the class or category name, and a label, each separated with a slash mark /: Custom/<class>/<method> or Custom/<category>/<name> (for example, Custom/MyClass/My_method).

<category>/<class>/<method>

class MetricSpec
  attr_accessor :name    # String - metric name
  attr_accessor :scope   # String - current controller action
end

class Stats
  attr_accessor :call_count           # Integer - method invocation count
  attr_accessor :total_call_time      # Float - total method call time (in seconds)
  attr_accessor :total_exclusive_time # Float - total time spent in the traced method minus any child time (in seconds)
  attr_accessor :min_call_time        # Float - the smallest method invocation time (in seconds)
  attr_accessor :max_call_time        # Float - the largest method invocation time (in seconds)
  attr_accessor :sum_of_squares       # Float - the sum of squares of response times - used for standard deviation computation
  attr_accessor :begin_time           # Time - the start of the time window for this data
  attr_accessor :end_time             # Time - end of the time window for this data
end

Record custom metrics

The public API for recording metric data consists of two methods on NewRelic::Agent, record_metric and increment_metric.

record_metric(metric_name, value)

record_metric should be used to record an event-based metric, usually associated with a particular duration. metric_name must be a String following standard metric naming rules. value will usually be a Numeric, but may also be a Hash.

When value is a numeric value, it should represent the magnitude of a measurement associated with an event, such as the duration for a particular method call.

When value is a Hash, it must contain :count, :total, :min, :max, and :sum_of_squares keys, all with Numeric values. This form is useful if you wish to aggregate metrics on your own and report them periodically (for example, from a background thread). The provided stats will be aggregated with any previously collected values for the same metric. The names of the hash keys have been chosen to match the names of the keys used by the platform API.

increment_metric(metric_name, amount=1)

increment_metric should be used to update a metric that acts as a simple counter. The count of the selected metric will be incremented by the specified amount.

Example custom metric

Here is an example that shows how you might use metrics to track currency flowing through a site:

class Cart

  def checkout()
    amount = compute_cart_total    # computes the amount to charge the customer

    ::NewRelic::Agent.record_metric('Custom/Cart/charge_amount', amount)

    charge_customer(amount)
    ...
  end
end

For more information about how data aggregates over time, see Stat aggregation policy.

View custom metrics

To view these custom metrics, use the query builder to search metrics, create customizable charts, and add those charts to dashboards.