MultiJsonのBackendをyajlに変えたら素のjson.gemの2倍のパフォーマンスになった件

json_bench.rb

#!/usr/bin/env ruby 

# rails r tools/json_bench.rb

require 'rbench'

ar_objects1 = # 適当なActiveRecordオブジェクト一個
json_str1   = ar_objects1.to_json
ar_objects2 = # 3個ほど子テーブルをincludeさせたActiveRecordオブジェクトを70個くらいの配列に
json_str2   = ar_objects2.to_json

puts ""
puts "-" * 80
puts "Benchmark of json encoding/decoding"
puts "  json_gem vs yajl"
puts "-" * 80
puts ""

RBench.run(10000) do

  column :times
  column :one,  :title => "json_gem"
  column :two,  :title => "yajl"
  column :diff, :title => "json_gem/yajl", :compare => [:one,:two]

  group 'Single ActiveRecord Object ' do
    report 'encode' do
      # ActiveSupport::JSON.encode
      one {
        MultiJson.engine = :json_gem unless MultiJson.engine.name == 'MultiJson::Adapters::JsonGem'
        ar_objects1.to_json
      }

      # as_json and MultiJson.encode with yaji
      two {
        MultiJson.engine = :yajl unless MultiJson.engine == MultiJson::Adapters::Yajl
        MultiJson.encode(ar_objects1.as_json)
      }
    end

    report 'decode' do
      # ActiveSupport::JSON.decode with json_gem
      one {
        MultiJson.engine = :json_gem unless MultiJson.engine == MultiJson::Adapters::JsonGem
        ActiveSupport::JSON.decode(json_str1)
      }
      # ActiveSupport::JSON.decode with yaji
      two {
        MultiJson.engine = :yajl unless MultiJson.engine == MultiJson::Adapters::Yajl
        ActiveSupport::JSON.decode(json_str1)
      }
    end
  end

  group 'Array  ActiveRecord Objects' do
    report 'encode' do
      # ActiveSupport::JSON.encode
      one {
        MultiJson.engine = :json_gem unless MultiJson.engine == MultiJson::Adapters::JsonGem
        ar_objects2.to_json
      }

      # as_json and MultiJson.encode with yaji
      two {
        MultiJson.engine = :yajl unless MultiJson.engine.name == 'MultiJson::Adapters::Yajl'
        MultiJson.encode(ar_objects2.as_json)
      }
    end

    report 'decode' do
      # ActiveSupport::JSON.decode with json_gem
      one {
        MultiJson.engine = :json_gem unless MultiJson.engine.name == 'MultiJson::Adapters::JsonGem'
        ActiveSupport::JSON.decode(json_str2)
      }
      # ActiveSupport::JSON.decode with yaji
      two {
        MultiJson.engine = :yajl unless MultiJson.engine.name == 'MultiJson::Adapters::Yajl'
        ActiveSupport::JSON.decode(json_str2)
      }
    end
  end
end

ruby_json_bench.txt

--------------------------------------------------------------------------------
Benchmark of json encoding/decoding
  json_gem vs yajl
--------------------------------------------------------------------------------

                                            | json_gem |    yajl | json_gem/yajl |
--Single ActiveRecord Object -----------------------------------------------------
encode                               x10000 |   12.130 |   6.167 |         1.97x |
decode                               x10000 |    1.085 |   0.437 |         2.48x |
--Array  ActiveRecord Objects-----------------------------------------------------
encode                               x10000 |  508.319 | 225.235 |         2.26x |
decode                               x10000 |   39.069 |  19.869 |         1.97x |