caching_instrumentation.rb

if ENV['INSTRUMENT_CACHE_KEYS']

  class CacheKeyInstrumenter
    include Singleton

    def hit(payload)
      record :hits, payload
    end

    def miss(payload)
      record :misses, payload
    end

    private

    def record(what, payload)
      k = key_head(payload[:key])

      StatsD.increment("#{App.statsd_context}.cache.#{k}.#{what}")
    end

    def key_head(key)
      key.split('/').first.gsub(/[#\.]/, '__')
    end
  end

  ########

  ActiveSupport::Notifications.subscribe('cache_fetch_hit.active_support') do |name, start, finish, id, payload|
    CacheKeyInstrumenter.instance.hit(payload)
  end

  ActiveSupport::Notifications.subscribe('cache_generate.active_support') do |name, start, finish, id, payload|
    CacheKeyInstrumenter.instance.miss(payload)
  end

end