multi_cache_serializer.rb

module ActiveModel
  class MultiCacheSerializer < ArraySerializer
    # XXX ArraySerializer の実装に依存しまくっている
    def serializable_array
      return super unless perform_caching && cache

      entries = object.each_with_object({}) {|item, memo|
        if options.has_key?(:each_serializer)
          serializer = options[:each_serializer]
        elsif item.respond_to?(:active_model_serializer)
          serializer = item.active_model_serializer
        end

        serializer ||= ActiveModel::DefaultSerializer
        serializable = serializer.new(item, options.merge(root: nil))

        if serializable.respond_to?(:serializable_hash)
          key = expand_cache_key([serializable.class.to_s.underscore, serializable.cache_key, 'serialize'])
          val = -> { serializable.serializable_hash }
        else
          key = expand_cache_key([serializable.class.to_s.underscore, serializable.cache_key, 'to-json'])
          val = -> { serializable.as_json }
        end

        memo[key] = val
      }

      cached = cache.read_multi(*entries.keys)

      entries.map {|key, val|
        if cached.has_key?(key)
          cached[key]
        else
          val.call.tap {|data|
            cache.write key, data
          }
        end
      }
    end
  end
end

newrelic.rb

begin
  require 'new_relic/agent/method_tracer'
rescue LoadError
  # do nothing
else
  DependencyDetection.defer do
    @name = :active_model_serializers

    depends_on do
      defined?(ActiveModel::Serializer) && !NewRelic::Control.instance['disable_active_model_serializers']
    end

    executes do
      NewRelic::Agent.logger.debug 'Installing ActiveModel::Serializers instrumentation'
    end

    executes do
      ActiveModel::Serializer.class_eval do
        include NewRelic::Agent::MethodTracer

        add_method_tracer :serializable_hash, 'Serializer/#{self.class.name}/serialize'
      end
    end
  end
end

rake stats

+----------------------+-------+-------+---------+---------+-----+-------+
| Name                 | Lines |   LOC | Classes | Methods | M/C | LOC/M |
+----------------------+-------+-------+---------+---------+-----+-------+
| Controllers          |   676 |   495 |      27 |      71 |   2 |     4 |
| Helpers              |     2 |     2 |       0 |       0 |   0 |     0 |
| Models               |   426 |   321 |      23 |      35 |   1 |     7 |
| Mailers              |    21 |    18 |       1 |       2 |   2 |     7 |
| Javascripts          |  2362 |  1663 |       0 |     323 |   0 |     3 |
| Libraries            |    88 |    74 |       4 |       6 |   1 |    10 |
| Feature specs        |  1322 |   948 |       0 |       2 |   0 |   472 |
| Lib specs            |    66 |    50 |       0 |       2 |   0 |    23 |
| Controller specs     |   264 |   191 |       0 |       0 |   0 |     0 |
| Cell specs           |   439 |   355 |       0 |       0 |   0 |     0 |
| Mailer specs         |     4 |     3 |       0 |       0 |   0 |     0 |
| Model specs          |   204 |   151 |       0 |       0 |   0 |     0 |
| Serializer specs     |   151 |   111 |       0 |       0 |   0 |     0 |
+----------------------+-------+-------+---------+---------+-----+-------+
| Total                |  6025 |  4382 |      55 |     441 |   8 |     7 |
+----------------------+-------+-------+---------+---------+-----+-------+
  Code LOC: 2573     Test LOC: 1809     Code to Test Ratio: 1:0.7

user_serializer.rb

class UserSerializer < ApplicationSerializer
  attributes :id, :name, :gravatar_id, :status
end

users_controller.rb

class Api::UsersController < Api::ApplicationController
  def index(ids = nil)
    @users = User.accessible_by(current_user)
    @users = @users.where(id: ids) if ids

    render json: @users
  end

  def show(id)
    render json: User.accessible_by(current_user).find(id)
  end
end