Caching

Introduction

Rails provides three types of caching: page, action, and fragment caching
Page caching creates whole html pages under public that get served by the web server without touching Rails. It’s appropriate for pages that look the same for all users.
Action caching caches only the output of an action. Filters (i.e. authentication) still get run.
With fragment caching you can cache certain expensive elements on a page, i.e. a menu or a list of recent content.
You can use Memcached with plugins such as Cached Model and Cache Fu to cache some or all of your database queries

Cache Methods and Configuration


caches_page :public_action
expire_page :action => 'public_action'
caches_action :premium_content
caches_action :premium_content, :layout => false # don't cache the layout
expire_action :action => 'premium_content', :id => 2
cache 'recent_products'
expire_fragment 'recent_products'

# Configuration:
config.action_controller.perform_caching = true

Cache Storage

You can store fragments in file system, DRb, memcached
If you have multiple servers and store in the file system you need to setup a shared network drive
Page caches are always kept as HTML files under the public directory and needs sharing across servers as well

Cache Sweepers


class ArticleSweeper < ActionController::Caching::Sweeper
  observe Article
  def after_create(article) 
    expire_page(:controller => "content", :action => 'public_content') 
  end 
  def after_update(article)
    expire_action(:controller => "content",  :action => "premium_content", :id => article_id) 
  end 
  def after_destroy(article) 
    ...
  end 
end

Hooking up the Cache Sweeper


class ContentController < ApplicationController 
  cache_sweeper :article_sweeper, :only => [ :create_article, :update_article, :delete_article ]
end

Fragment Caching

Fragment caching is used for pages where only certain parts (fragments) should be cached whereas other parts should be dynamic
Parts of the page that should be cached are included in a <% cache ‘cache_name’ do > ... < end %> block.
You expire cached fragments with an invocation such as expire_fragment(‘cache_name’)

Fragment Cache Storage


ActionController::Base.cache_store = :memory_store
ActionController::Base.cache_store = :file_store, "/path/to/cache/directory" 
ActionController::Base.cache_store = :drb_store, "druby://localhost:9192" 
ActionController::Base.cache_store = :mem_cache_store, "localhost" 
ActionController::Base.cache_store = MyOwnStore.new("parameter")

Conditional Gets – ETags


def show
  @article = Article.find(params[:id])
  response.last_modified = @article.published_at.utc
  response.etag = @article

  if request.fresh?(response)
    head :not_modified
  else
    respond_to do |wants|
      # normal response processing
    end
  end
end

Copyright © 2009 Peter Marklund

Caching

Introduction

Cache Methods and Configuration

Cache Storage

Cache Sweepers

Hooking up the Cache Sweeper

Fragment Caching

Fragment Cache Storage

Conditional Gets – ETags