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For the sidebar content in MeinProf.de we use fragment caching. One problem with caching is that expiring entries can get really messy. Time-based caching can solve this problem but the current caching implementation in Rails does not support this.

While poking around in the MemCache-client implementation from the Robotcoop I saw that MemCache itself does support time-based expiry of cached entries. Thanks to Ruby I just re-implemented the write method in ActionController::Caching::Fragments::MemCacheStore so that we could expire our entries after some given time:

class ActionController::Caching::Fragments::MemCacheStore

  def write(name, value, options=nil)

    @data.set(name, value, 30.minutes)

  end

end

Now all fragments expire after 30 minutes. If you want to have different live-times for your caches you have to distinct by the name of the fragment. Normally fragments created with the <% cache do %> call in views are named after the controller and action, e.g. controller/actionname. You can also specify a name like <% cache("UniPage_#{uni.id}") do %>.

class ActionController::Caching::Fragments::MemCacheStore

  def write(name, value, options=nil)

    if name =~ %r{^UniPage}

      @data.set(name, value, 30.minutes)

    elsif name == "mycontroller/myaction"

      @data.set(name, value, 45.minutes)

    else

      @data.set(name, value, 60.minutes)

    end

  end

end

Not the cleanest solution but it works very well for us.

If you want to also save your sessions in MemCache with the memcache-client library from the Robotcoop, add this code to ActionController::Caching::Fragments::MemCacheStore:

class ActionController::Caching::Fragments::MemCacheStore

  def data=(cache)

    @data = cache

  end

end

In summary our code in config/environments/production.rb looks like this:

### MemCached Server ###

CACHE = MemCache.new :c_threshold => 10_000, :compression => true,\
 :debug => false, :namespace => 'meinprof_de', :readonly => false, :urlencode => false


CACHE.servers = '127.0.0.1:11211'



### Sessions in MemCached ###

session_options = {

    :database_manager => CGI::Session::MemCacheStore,

    :cache => CACHE

}



ActionController::CgiRequest::DEFAULT_SESSION_OPTIONS.update session_options



### FragmentCaching im MemCached ###

# Allow us to set the CACHE as the Fragment Cache store

class ActionController::Caching::Fragments::MemCacheStore

  def data=(cache)

    @data = cache

  end

  

  def write(name, value, options=nil)

    if name =~ %r{^Random_TopFlop}

      @data.set(name, value, 30.minutes)

    elsif name =~ %r{^RegionPage}

      @data.set(name, value, 60.minutes)

    elsif name =~ %r{^UniPage}

      @data.set(name, value, 60.minutes)    

    else

      @data.set(name, value, 120.minutes)

    end

  end

end


ActionController::Base.fragment_cache_store = :mem_cache_store ,{}

ActionController::Base.fragment_cache_store.data = CACHE