local_cache
===========

This plugin extends any cache store configured in rails with a process local in memory cache. It is intended to be a 
Rails 2.2 replacement for the extended_fragment_cache plugin (http://rubyforge.org/projects/zventstools/) which does 
essentially the same but doesn't work with the new caching infrastructure in Rails >= 2.1.

Adding a local cache to the usual remote cache (memcache, file etc.) has two major advantages over the default behaviour 
(for fragment caching):

* you usually need two cache requests per http request: one in the controller to determine if the cached fragment is 
still there, one in the view where the fragment is actually rendered - that means the number of cache roundtrips get cut 
in half
* the following scenario is avoided: request comes into controller, controller fetches fragment from remote cache, does 
not assign certain variables as the cache is primed, cache is expired by another process, view gets rendered, cache 
fragment is deleted - boom

installation
============

script/plugin install git://github.com/langalex/local_cache.git

the plugin automatically replaces the current cache storage with a proxy that handles the local caching and delegates 
the rest to the original storage.

usage
=====

The plugin provides a method in your controller called when_fragment_expired, which takes a key name and a block:

class MyController
  def index
    when_fragment_expired 'my_index', 60.minutes do
      @data = Data.find :all
    end
  end
end

The code in the block only gets executed when the cache returns no data for the given key. In the view you do the normal


<%- cache 'my_index' do -%>
  <%- @data.each do |data| -%>
    <%= data.content %>
  <%- end -%>
<%- end -%>

This loads the fragment from the local cache and renders it. If the cache returns nil the block gets executed, written 
to the cache and rendered as ususal in rails. Before every request, the local cache is cleared so no stale data gets 
into your application.


By the way with memcache you can expire your cache fragments by time like this: (this is not part of this plugin but the 
default behavior)

<%- cache 'my_index', 60.minutes do -%>
  <%- @data.each do |data| -%>
    <%= data.content %>
  <%- end -%>
<%- end -%>

This will expire the fragment after 60 minutes.


Contact
=======

Copyright (c) 2008 Alexander Lang, Thilo Utke, released under the MIT license

Contact: 

email: alex[at]upstream-berlin.com, twitter: langalex, blog: http://upstream-berlin.com/blog, skype: langalex
       thilo[at]upstream-berlin.com