.rb

# add to config/environments/production.rb or development.rb

require "appengine_mem_cache_store.rb"
config.cache_store = AppEngine::Memcache::RailsStore.new(:namespace=>"cache_store")
config.action_controller.perform_caching = true

appengine_mem_cache_store.rb

require 'appengine-apis/memcache'
module AppEngine
  class Memcache
    class RailsStore < ActiveSupport::Cache::Store
      def initialize(opts={})
        @data = AppEngine::Memcache.new(opts)
       #extend ActiveSupport::Cache::Strategy::LocalCache
      end

      # Reads multiple keys from the cache.
      def read_multi(*keys)
        @data.get_multi keys
      end

      def read(key, options = nil) # :nodoc:
        super
        @data.get(key)
      rescue MemcacheError => e
        logger.error("MemcacheError (#{e}): #{e.message}")
        nil
      end

      # Writes a value to the cache.
      #
      # Possible options:
      # - +:unless_exist+ - set to true if you don't want to update the cache
      #   if the key is already set.
      # - +:expires_in+ - the number of seconds that this value may stay in
      #   the cache. See ActiveSupport::Cache::Store#write for an example.
      def write(key, value, options = nil)
        super
        method = options && options[:unless_exist] ? :add : :set
        response = @data.send(method, key, value, expires_in(options))
        response == true
      rescue MemcacheError => e
        logger.error("MemcacheError (#{e}): #{e.message}")
        false
      end

      def delete(key, options = nil) # :nodoc:
        super
        response = @data.delete(key, expires_in(options))
        response == true
      rescue MemcacheError => e
        logger.error("MemcacheError (#{e}): #{e.message}")
        false
      end

      def exist?(key, options = nil) # :nodoc:
        # Doesn't call super, cause exist? in memcache is in fact a read
        # But who cares? Reading is very fast anyway
        # Local cache is checked first, if it doesn't know then memcache itself is read from
        !read(key, options).nil?
      end

      def increment(key, amount = 1) # :nodoc:
        log("incrementing", key, amount)
        response = @data.incr(key, amount)
        response
      rescue MemcacheError
        nil
      end

      def decrement(key, amount = 1) # :nodoc:
        log("decrement", key, amount)
        response = @data.decr(key, amount)
        response
      rescue MemcacheError
        nil
      end

      def delete_matched(matcher, options = nil) # :nodoc:
        # don't do any local caching at present, just pass
        # through and let the error happen
        super
        raise "Not supported by Memcache"
      end

      def clear
        @data.flush_all
      end

      def stats
        @data.stats
      end
    end
  end
end