ActiveRecordでSlowQueryを通知する方法 ref: http://qiita.com/dtaniwaki/items/2acf9e7f54eec05d48f3

main.rb

# Detect slow query slower than 1000 msec
Ext::ActiveRecord::SlowQuerySubscriber.load!(1000)

slow_query_subscriber.rb

module Ext::ActiveRecord
  class SlowQuerySubscriber < ActiveSupport::Subscriber
    class SlowQuery < StandardError
    end

    cattr_accessor :threshold

    def self.load!(threshold)
      self.threshold = threshold
      attach_to :active_record
    end

    def sql(event)
      if event.duration > self.threshold
        e = SlowQuery.new("Found slow query #{event.payload[:sql].inspect} : #{event.duration} msec > #{self.threshold} msec")
        e.set_backtrace caller
        ActiveRecord::Base.logger.warn(e.message)
        Bugsnag.notify_or_ignore(e, severity: "warning", grouping_hash: event.payload[:sql], payload: event.payload, duration: event.duration)
      end
    end
  end
end