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Action cache

Drop in replacement for the Action Cache to provide a better cache.

From the README:

Contributors:

  • Tom Fakes (tom@craz8.com) - Initial implementation, plugin implementation, x-sendfile work
  • Scott Laird - Ideas for the timed expiry and programmable fragment_key features

Action Cache Upgrade

This is a drop in replacement for the Rails Action Cache. When this plugin is installed, the new behavior will take effect without any further configuration.

All documentation for the Rails Action Cache is still relevant. Sweepers still work, all the fragment stores are supported.

See my blog at http://blog.craz8.com to find some interesting uses of the extended behavior provided by this plugin

Major Change!

This version uses a different cache key generation mechanism. Instead of setting ActionController::Caching::Actions::ActionCacheFilter.fragment_key, the cache code calls out to the action_fragment_key method on the current controller. A default version of this method is supplied that emulates the Rails built in Action Cache. If you haven’t set the fragment_key in your code, then nothing changes. If you have set the fragment_key, then you will need to move that code to the application controller for your code to continue working.

Features

  1. Store cache entries as YAML streams so the Response headers from the original response can be returned with cache hits
  2. Add a ‘last-modified’ header to the response to get the client to use a get-if-modified request
  3. If the client has the response we have cached, don’t send it again, send a ‘304 Not Modified’ response to reduce data on the wire
  4. Fix a bug in the original Rails code where responses other than ‘200 OK’ are cached (since the headers aren’t cached in the original, all the clients would get is an empty ‘200 OK’ response from subsequent requests)
  5. Allow clients to provide their own implementation of the cache key for the actions, e.g.
         - application.rb
    
           # Cache different pages for Admin and Users
       def action_fragment_key(options)
         url_for(options).split('://').last + "/#{admin? : 'admin' : 'user'}"
       end
    

    The options hash can be used to pass parameters in to override the current controller, and is used by the cache expiry code to expire an action from a sweeper or a different controller than the one the action is cached for.

  6. Allow an action to specify a Time To Live for the cached item. Set ‘response.time_to_live’ to the number of seconds before this cached item will be expired. If not set, the default setting of ‘never’ will be used and the item will only be expired by using the regular action cache expiry mechanism.
      def my_action
        @response.time_to_live = 10.minutes
        ...
      end
    
  7. If the ENABLE_X_SENDFILE environment variable is set, or the HTTP_ENABLE_X_SENDFILE request header is set, and the fragment cache is set to the FileStore, then the Action Cache code will not return the response body, but will set the X-Sendfile header in the response to the filename of the cache entry that contains the body.
   Be sure your web server is has the X-Sendfile feature enabled, otherwise you'll just get   empty responses!

   Check out the lighttpd documentation for how to use the X-Sendfile feature: http://lighttpd.net/

   To enable this, the ENABLE_X_SENDFILE environment variable must be set, *and* the FileStore fragment   cache must be used.

   lighttpd.conf:

        fastcgi.server = ( ".fcgi" =>
                ( "app" =>
                (         "min-procs" => 1,
                        "max-procs" => 1,
                                "allow-x-send-file" => "enable",
                        "socket"    => "/tmp/app.fcgi.socket",
                        "bin-path"  => "/path/to/app/public/dispatch.fcgi",
                        "bin-environment" => ( "RAILS_ENV" => "development", "ENABLE_X_SENDFILE" => "true" )
                )
                )
        )

   environment.rb:
     ActionController::Base.fragment_cache_store = :file_store, "/path/to/cache/directory"

   Note: The cache directory can be anywhere on your server that your web server user has read and write    access to.  This should *not* be in the Rails /public directory.
  1. Control whether caching occurs for an action at runtime instead of load time.

    To control caching, add a method *cache_action?(action_name)* to your controller. If this method returns true, then the action cache will work as before. If false, then caching will not occur for this request.

    e.g.

          class ApplicationController < ActionController::Base
             ...
    
             def cache_action?(action_name)
               !admin?
             end
    
                 ...
      end
    
         Note: The action must still be marked for caching by adding *caches_action :action* to the controller
    
  2. If the ENABLE_X_ACCEL_REDIRECT request header is set, and the fragment cache is set to the FileStore, then the Action Cache code will not return the response body, but will set the X-Accel-Redirect header in the response to the filename of the cache entry that contains the body.

    The nginx configuration must contain a ‘location’ section labeled ‘cache’, that points to the location you have configured for your Rails fragment cache, default is RAILS_ROOT/tmp/cache. e.g:

      location /cache/ {
         internal;
         root   /path/to/rails/app/current/tmp;
      }
    

    To enable this, the ENABLE_X_SENDFILE environment variable must be set, and the FileStore fragment cache must be used.

    nginx.conf:

     location /cache/ {
       internal;
       root   /path/to/rails/app/current/tmp;
     }
    
     location / {
       proxy_set_header  X-Real-IP  $remote_addr;
       proxy_set_header  X-Forwarded-For $proxy_add_x_forwarded_for;
       proxy_set_header Host $http_host;
       proxy_set_header "ENABLE_X_ACCEL_REDIRECT" "true";
            ...
         }
    

    environment.rb:

      ActionController::Base.fragment_cache_store = :file_store, "/path/to/cache/directory"
    

    Note: The cache directory can be anywhere on your server that your web server user has read and write access to. This should not be in the Rails /public directory.

  3. A new method ‘expire_all_actions’ will clear out the entire action cache contents.
  4. expire_action will now work with the custom generated action cache keys, so your cache expiry calls and sweepers will work correctly.

    The expire_action call implemented here will actually use the Regexp fragment expiry call, causing all matching cache items to be cleared. For those of you using REST, and providing HTML, JS and XML for the same action, all three will be expired when you expire one of them with code like:

        # Expires all formats of the action
        expire_action :controller => 'foo', :action => 'bar'
    

Performance

If a client requests an action whose output hasn’t changed since their last request, the returning of a 304 response instead of the full response greatly reduces the load on the server.

In my informal testing, with the X-Sendfile enabled, I was able to get about 20% more requests out of my rails application, based on the requests-per-second displayed in the rails log. This doesn’t mean the request is faster, but that the work of delivering the content is offloaded to the web server from the Rails app.

Vitals

Home http://blog.craz8.com
Repository http://craz8.com/svn/trunk/plugins/action_cache
License Rails' (MIT)
Rating (23 votes)
Owner Tom Fakes
Created 14 April 2006

Comments

  • Avatar
    chris
    17 July 2007

    Great plugin. One issue I'm having is that occasionally something goes wrong with a request (unrelated to your plugin), the META is properly cached, but the DATA file is empty or non-existant. Your plugin checks for the existance of the META file, but doesn't do any validation that the DATA file is there and properly generated.

  • Avatar
    chris
    17 July 2007

    Also, by default it will cache POST and HEAD, which will have an empty response body that will then be rendered as empty for GET's as well.

  • Mark
    1 April 2008

    Very useful.

    One speed improvement would be to avoid having to read the whole of the cached page from disk via readfragment before doing an xsendfile or xaccelredirect, doing a File.size? instead.

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