DB metrics broken out by host

db_metrics.rb

ActiveSupport::Notifications.subscribe('sql.active_record') do |name, start_time, end_time, guid, opts|
  connection_id = opts[:connection_id]
  if connection_id
    conn = ObjectSpace._id2ref(connection_id)
    if conn
      config = conn.instance_variable_get(:@config)
      if config
        host    = config[:host]
        adapter = config[:adapter]
        if host && adapter
          metric   = "ShardQueries/sql/#{adapter}/#{host}"
          duration = end_time - start_time

          NewRelic::Agent.record_metric(metric, duration)
        end
      end
    end
  end
end