ar_bench.rb

require 'active_record'
require 'identity_cache'
require 'logger'

logger = Logger.new nil
ActiveRecord::Base.establish_connection(adapter: 'mysql2', database: 'test', username: 'root')

IdentityCache.cache_backend = ActiveSupport::Cache::MemCacheStore.new
IdentityCache.logger = logger
class Image < ActiveRecord::Base
  connection.create_table table_name, force: true do |t|
    t.integer :product_id
  end

  include IdentityCache
  belongs_to :product
end

class Product < ActiveRecord::Base
  connection.create_table table_name, force: true do |t|
  end

  include IdentityCache
  has_many :images
  cache_has_many :images, :embed => true

#  has_many :pictures, class_name: 'Image'
#  cache_has_many :pictures, :embed => true
end

product = Product.create!
3.times { Image.create!(product: product) }
id = product.id

Benchmark.bm do |x|
  x.report do
    100_000.times do
      Product.fetch(id)
    end
  end
end

results:

before:

       user     system      total        real
  36.310000   2.480000  38.790000 ( 39.942972)

after:

       user     system      total        real
  21.880000   2.200000  24.080000 ( 24.851130)

rails 3:

       user     system      total        real
  20.220000   2.040000  22.260000 ( 23.073374)