A monkey patch to speed up Rails's json generation time
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lib/rails/patch/json bump version Aug 22, 2014



This is a monkey patch for Rails in order to speed up its JSON encoding, and to draw people's attention to this Rails issue.

For full details please read Jason Hutchens' blog post.

All credits goes to Jason Hutchens for discovering the issue and providing the code for this monkey patch.


First, go to your Rails console and type:

data = Hash.new
key = 'aaa'
1000.times { data[key.succ!] = data.keys }
1000 * Benchmark.realtime { data.to_json }

See how Rails performs before the patch.

Second, bundle install this gem with a fast JSON encoding gem in your Rails' Gemfile.

gem 'rails-patch-json-encode'
gem 'oj'

In this case I choose the oj gem, but you can choose a json-encoder gem that multi_json supports.

Last, there are two levels of patch available. You have to choose one and call it explictly:

  • Rails::Patch::Json::Encode.patch_base_classes patches all Ruby base classes.
  • Rails::Patch::Json::Encode.patch_renderers patches Rails' ActionController::Renderers only. This is for those who had issue with the JSON gem, as patching base classes cause infinite recursive loop.

Place one of them in Rails' initializers like config/initializers/rails_patch_json_encode.rb, and Rails should now use the faster encoder.


For console benchmark comparison, restart console after the above installation. Call Rails::Patch::Json::Encode.patch_base_classes in console, then re-run the test to see how the performance changes.

The actual performance boost on real-world applications will probably be less than that. For one of my page I see the rendering time dropped by 25%.


This gem may break your app. Test your app. I am not sure if this is production ready.

What's with the name

This is just a temporal monkey patch, and a monkey patch isn't supposed to have a fancy name.

Related reading


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request