ActiveSupport::Subscriber

ActiveSupport::Subscriber is an object set to consume ActiveSupport::Notifications. The subscriber dispatches notifications to a registered object based on its given namespace.

An example would be Active Record subscriber responsible for collecting statistics about queries:

module ActiveRecord
  class StatsSubscriber < ActiveSupport::Subscriber
    def sql(event)
      Statsd.timing("sql.#{event.payload[:name]}", event.duration)
    end
  end
end

And it’s finally registered as:

ActiveRecord::StatsSubscriber.attach_to :active_record

Since we need to know all instance methods before attaching the log subscriber, the line above should be called after your subscriber definition.

After configured, whenever a “sql.active_record” notification is published, it will properly dispatch the event (ActiveSupport::Notifications::Event) to the sql method.