gistfile2.rb

require 'active_record'
require 'benchmark'
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.integer :comments_count
  end

  create_table :comments, force: true do |t|
    t.integer :post_id
  end
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post, counter_cache: true
end

10.times do
  post = Post.create!
  Comment.create!(post: post)
end

record = Post.first
association_name = :comments

if 'prof' == ARGV[0]
  require 'stackprof'
  mode = ARGV[1] || 'cpu'
  StackProf.run(mode: mode.to_sym, out: "tmp/stackprof-#{mode}-reader-rails#{ActiveRecord::VERSION::STRING}.dump") do
    100_000.times do
      reflection = record.class.reflect_on_association(association_name)
      association = reflection.association_class.new(record, reflection)
      association.reader
    end
  end
else
  Benchmark.bm do |x|
    x.report do
      100_000.times do
        reflection  = record.class.reflect_on_association(association_name)
        association = reflection.association_class.new(record, reflection)
        association.reader
      end
    end
  end
end