Ruby on Rails Web development framework is extremely popular for rapid development of Web applications and, at some point in time it started an actual movement for a set of convention-over-configuration frameworks and most likely you have used one of them recently if you are a seasoned web developer.
We are assuming that you are familiar with Rails and you already have some experience using rails caching API, but even if you are not, that's a good introduction about caching in Rails anyway.
We will be using Dalli as the memcached client and we will be configuring a simple Rails application to use it as a backend for Rails Caching. If you want more information about Rails caching in general, you are advised to visit http://guides.rubyonrails.org/caching_with_rails.html.
You will need to have a working Rails installation on your system for that, you can find great tutorials on the Web for that, such as this one https://www.digitalocean.com/community/articles/how-to-install-ruby-on-rails-on-ubuntu-12-04-lts-precise-pangolin-with-rvm.
Let's now start by creating a really simple Rails application as a mock, to be the test base for our caching experiments:
rails new cachesample.In a few minutes, you will have your empty Rails application ready, you can run it using:
cd cachesample/ rails server
You should see something like the following:
=> Booting WEBrick => Rails 4.0.0 application starting in development on http://0.0.0.0:3000 => Run `rails server -h` for more startup options => Ctrl-C to shutdown server [2013-10-29 16:40:56] INFO WEBrick 1.3.1 [2013-10-29 16:40:56] INFO ruby 2.0.0 (2013-06-27) [x86_64-linux] [2013-10-29 16:40:56] INFO WEBrick::HTTPServer#start: pid=18450 port=3000
Now, we need to configure our Rails application to use Dalli gem as a dependency.
Edit your
Gemfileand add this line at the end of the file:gem 'dalli'
Then, you will need to run:
bundle install
Now, we need to edit the application configuration to actually use memcached as the caching backend for the rails caching API.
Normally, you don't enable caching while development and you only turn it on in production, so we will be editing the config/environments/production.rb file (you may also want to add this to config/environments/development.rb if you want to see caching in development mode). Let's add:
config.cache_store = :dalli_store
You will be able to use all of Rails automatic and manual caching features of Rails and the default cache store will be now Dalli (memcached client).
Rails has different features for caching, such as the following:
Action caching: It caches an action response based on the input parameters and every request will go to all the before filters, this means that authentication is verified for example.
Fragment caching: This means that specific pieces of template code can be cached, this is very useful, specially if you are building a huge page that contains pieces that are constantly changing and dynamic, you still can modularize parts of the page and cache those parts as fragments. For example, you want to cache a fragment that generates a list of products:
<% Order.find_recent.each do |o| %> <%= o.buyer.name %> bought <%= o.product.name %> <% end %> <% cache do %> All available products: <% Product.all.each do |p| %> <%= link_to p.name, product_url(p) %> <% end %> <% end %>
SQL caching: This is a feature that allows Rails to cache results of a SQL query so that if it encountered the same query again for that request, it will use the cached result set and will not be running the same query again on the database server.
To use Dalli for Rails session storage that times out after 20 minutes, in config/initializers/session_store.rb:
config.cache_store = :dalli_store, 'cache-1.example.com', 'cache-2.example.com',
{ :namespace => NAME_OF_RAILS_APP, :expires_in => 1.day, :compress => true }Of course, you will need to write the correct names of the memcached hosts and ports for your caching cluster, instead of cache-1.example.com and cache-2.example.com.