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Metrics instrumentation guide

This guide describes how to develop Usage Ping metrics using metrics instrumentation.

Nomenclature

Instrumentation class:
- Inherits one of the metric classes: DatabaseMetric, RedisHLLMetric or GenericMetric.
- Implements the logic that calculates the value for a Usage Ping metric.
Metric definition The Usage Data metric YAML definition.
Hardening: Hardening a method is the process that ensures the method fails safe, returning a fallback value like -1.

How it works

A metric definition has the instrumentation_class field, which can be set to a class.

The defined instrumentation class should have one of the existing metric classes: DatabaseMetric, RedisHLLMetric, or GenericMetric.

Using the instrumentation classes ensures that metrics can fail safe individually, without breaking the entire process of Usage Ping generation.

We have built a domain-specific language (DSL) to define the metrics instrumentation.

Database metrics

Example of a merge request that adds a database metric.

module Gitlab
  module Usage
    module Metrics
      module Instrumentations
        class CountBoardsMetric < DatabaseMetric
          operation :count

          relation { Board }
        end
      end
    end
  end
end

Redis HyperLogLog metrics

Example of a merge request that adds a RedisHLL metric.

Count unique values for i_quickactions_approve event.

time_frame: 28d
data_source: redis_hll
instrumentation_class: 'Gitlab::Usage::Metrics::Instrumentations::RedisHLLMetric'
options:
  events:
    - i_quickactions_approve

Generic metrics

Example of a merge request that adds a generic metric.

module Gitlab
  module Usage
    module Metrics
      module Instrumentations
        class UuidMetric < GenericMetric
          value do
            Gitlab::CurrentSettings.uuid
          end
        end
      end
    end
  end
end

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