Ruby custom metrics

Record arbitrary performance data via an API call (for example: timing or computer resource data). Then use Insights Metric Explorer to charts and track that metric. You can use custom metrics to unify your monitoring inside New Relic.

Collecting too many metrics can impact the performance of your application and your New Relic agent. To avoid data problems, keep the total number of unique custom metrics under 2000.

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).

Metric names and paths

Metric names are paths delimited by a slash mark /. For custom instrumentation use this pattern:

	<category>/<class>/<method>

To override the default metric name, pass a second argument to add_method_tracer. This may be necessary to specify a category other than the default Custom, or if the method and class name do not represent the metric well.

Reserved categories include:

  • ActiveRecord
  • Apdex
  • CPU
  • Controller
  • Database
  • Memory
  • View
  • Custom

For custom metric names, use Custom/<class>/<method> or Custom/<category>>/>name>

Metrics and stats in the Ruby agent

There are two basic data structures used to collect metric data: MetricSpec and Stats.

A MetricSpec is an identifier for which we have data. The following pseudo Ruby defines a metric:

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

The name identifies what the metric represents. The optional scope is the name of the controller action handling the current request. A metric is "global" if the scope is empty.

Metric values are recorded by Stats. Stats typically collects data about method execution but can store any interesting data. The following pseudo Ruby defines Stats:

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
Stat aggregation policy

One of New Relic's strengths is its ability to aggregate data over time. (Aggregation is the act of combining several things into one.) When collecting custom metrics, the aggregation policy can be important to know when collecting custom metrics. These include:

  • call_count: Addition
  • total_call_time: Addition
  • total_exclusive_time: Addition
  • min_call_time: Min() of each min_call_time
  • max_call_time: Max() of each max_call_time
  • sum_of_squares: Addition
  • begin_time: Min() of each begin_time
  • end_time: Max() of each end_time

Recording custom metrics

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

Both record_metric and increment_metric are thread safe.

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, e.g. 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 (e.g. 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.

Viewing custom metrics

To view these custom metrics, use Insights Metric Explorer to search metrics, create customizable charts, and add those charts to Insights dashboards.

For more help

Additional documentation resources include:

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If you need additional help, get support at support.newrelic.com.