bench_json_gems.rb

require "benchmark/ips"
require "granola"
require "json"
require "msgpack"
require "multi_json"
require "oj"
require "yajl"

User = Struct.new(:name, :age)

class UserSerializer < Granola::Serializer
  MIME_TYPES[:msgpack] = "application/x-msgpack".freeze

  def data
    { name: object.name, age: object.age }
  end

  def to_msgpack(*)
    MessagePack.pack(data)
  end
end

SERIALIZER = UserSerializer.new(User.new("John Doe", 30))

Benchmark.ips do |b|
  b.report("yajl") do
    Granola.json = ->(data, _) { Yajl::Encoder.encode(data) }
    10_1000.times { SERIALIZER.to_json }
  end

  b.report("json") do
    Granola.json = ->(data, _) { JSON.dump(data) }
    10_1000.times { SERIALIZER.to_json }
  end

  b.report("oj") do
    Granola.json = ->(data, _) { Oj.dump(data, mode: :compat) }
    10_1000.times { SERIALIZER.to_json }
  end

  b.report("msgpack") do
    10_1000.times { SERIALIZER.to_msgpack }
  end

  b.report("multi_json/yajl") do
    MultiJson.use :yajl
    Granola.json = MultiJson.method(:encode)
    10_1000.times { SERIALIZER.to_json }
  end

  b.report("multi_json/json") do
    MultiJson.use :json_gem
    Granola.json = MultiJson.method(:encode)
    10_1000.times { SERIALIZER.to_json }
  end

  b.report("multi_json/oj") do
    MultiJson.use :oj
    Granola.json = MultiJson.method(:encode)
    10_1000.times { SERIALIZER.to_json }
  end

  b.compare!
end

output.log

$ ruby -v
ruby 2.2.1p85 (2015-02-26 revision 49769) [x86_64-darwin14]

$ bundle show
Gems included by the bundle:
  * benchmark-ips (2.1.1)
  * bundler (1.9.2)
  * granola (0.10.1)
  * json (1.8.2)
  * msgpack (0.5.11)
  * multi_json (1.11.0)
  * oj (2.12.1)
  * yajl-ruby (1.2.1)

Calculating -------------------------------------
                yajl     1.000  i/100ms
                json     1.000  i/100ms
                  oj     1.000  i/100ms
             msgpack     1.000  i/100ms
     multi_json/yajl     1.000  i/100ms
     multi_json/json     1.000  i/100ms
       multi_json/oj     1.000  i/100ms
-------------------------------------------------
                yajl      1.731  (± 0.0%) i/s -      9.000
                json      1.329  (± 0.0%) i/s -      7.000  in   5.268963s
                  oj      3.250  (± 0.0%) i/s -     17.000
             msgpack      4.989  (± 0.0%) i/s -     25.000
     multi_json/yajl      1.011  (± 0.0%) i/s -      6.000  in   5.932494s
     multi_json/json      1.023  (± 0.0%) i/s -      6.000  in   5.865207s
       multi_json/oj      1.409  (± 0.0%) i/s -      8.000  in   5.677987s

Comparison:
             msgpack:        5.0 i/s
                  oj:        3.2 i/s - 1.54x slower
                yajl:        1.7 i/s - 2.88x slower
       multi_json/oj:        1.4 i/s - 3.54x slower
                json:        1.3 i/s - 3.75x slower
     multi_json/json:        1.0 i/s - 4.88x slower
     multi_json/yajl:        1.0 i/s - 4.93x slower