What is the fastest way to render json in rails

Currently oj seems to be the fastest renderer - beating yajl (according to the oj author's comparison).

Oj is used by default in the latest multi_json (and rails uses mutli_json by default), so swapping to oj should be as simple as adding the following to your Gemfile:

  # Gemfile  gem "oj"

Then each time you call render, it will now use oj.

  render :json => { ... } # uses multi_json which uses oj

Oj also provides additional specific interfaces, if you want even more performance, but sticking to multi_json makes it easier to swap out gems in the future.

Note that if you have any { ... }.to_json calls - these will not be upgraded to use oj unless you call Oj.mimic_JSON in an initializer.

Rails 3 uses multi_json, but it only uses it for json decoding, not encoding. Json encoding/rendering/generation uses ActiveSupport JSON library's to_json method, therefore is always slow (even if you uses Oj gem).

You can explicitly rendering using multi_json by doing:

render :json => MultiJson.dump(@posts)

Or you can try rails-patch-json-encode gem (by me) which will use multi_json by default. It will affect all build-in to_json methods, so make sure all the tests passes.

Rabl uses multi_json for compatibility across platforms and doesn't use the quite fast Yajl library by default. Rabl's config documentation explains the solution:

# Gemfilegem 'yajl-ruby', :require => "yajl"

In the event that still isn't performant enough, you might want to explore a different JSON serializer like oj. You could also instrument your render and see where the bottleneck exists.