Brief Overview of Caching in Ruby on Rails

Posted by Julee117 on May 9, 2018

Caching is the process of storing data so that future requests for that data can be served faster. This can improve the speed of your website and improve the user experience. There are various types of caching in Ruby on Rails such as:

  • HTTP caching
  • Model caching
  • Fragment caching
  • Action caching
  • Page caching

HTTP Caching

HTTP caching utilizes If-None-Match and If-Modified-Since headers. ETags aka entity tags are used to verify whether the page was modified. The server compares the current ETag to the one provided by the client and if they are both the same, it means that the page was not modified. However, if they do not match, the server will respond with a new ETag and the updated response.

Model Caching

Model caching aka low level caching caches a value or query result. The most efficient way to implement this is to use the Rails.cache.fetch method.

def cached 
  Rails.cache.fetch(“event”) { Event.all }

Rails.cache.fetch method reads and writes to the cache. It fetches data from the cache with the given key. If there is data, then the data is returned however if it is not, nil will be returned. In the case nil is returned and a block was passed, that block will be passed the key and executed where the return value of the block will be written to the cache.

Fragment Caching

In fragment caching, only a part of the page is being cached. For example, if we want to cache each event:

<% @events.each do |event| %>
  <% cache event do %>
    <%= event.title %> 
  <% end %>
<% end %> 

Page Caching

In page caching, the page is saved to a file inside the public directory. This allows future requests of sending the file without going through the entire Rails stack. However, we cannot use this for pages that need authentication. Page caching has been removed from Rails 4 so you need to add gem “actionpack-page_caching”.

Action Caching

Action caching is used for pages requiring authentication or other before/after filters. Add caches_action :<action_name> to your controller to turn on caching for specific actions.

class UsersController < ApplicationController
  caches_action :index

  def index
    @users = User.all


Action caching also has been removed from Rails 4 so you need to add gem “actionpack-page_caching”.

You can read further here on how to utilize the gem. To also read more about caching, you can find that here.