ar_bench.rb

["2.3.14.github42", "3.0.20", "3.1.12", "3.2.17", "4.0.4", "4.1.0"].each do |version|
  pid = fork do
    gem "activerecord", version
    require "active_record"

    puts "=====> ActiveRecord #{ActiveRecord::VERSION::STRING}"

    ActiveRecord::Base.establish_connection :adapter => "sqlite3", :database => ":memory:"

    class Foo < ActiveRecord::Base
      connection.execute "CREATE TABLE foos (id INTEGER PRIMARY KEY ASC, x INTEGER)"
      create :x => 123
    end

    foo = if ActiveRecord::VERSION::MAJOR < 4
            Foo.find(:first)
          else
            Foo.first
          end

    require "benchmark/ips"

    Benchmark.ips do |x|
      x.report("foo.x") do
        foo.x
      end
      x.report("Foo.find(1)") do
        Foo.find(1)
      end
      x.report("Foo.find_by_x(123)") do
        Foo.find_by_x(123)
      end
    end

    puts
  end

  Process.wait(pid)
end

results.txt

=====> ActiveRecord 2.3.14
Calculating -------------------------------------
               foo.x     41144 i/100ms
         Foo.find(1)       773 i/100ms
  Foo.find_by_x(123)       615 i/100ms
-------------------------------------------------
               foo.x  2409258.0 (±5.9%) i/s -   12014048 in   5.007349s
         Foo.find(1)     7898.8 (±2.7%) i/s -      40196 in   5.092745s
  Foo.find_by_x(123)     6470.1 (±3.3%) i/s -      32595 in   5.043230s

=====> ActiveRecord 3.0.20
Calculating -------------------------------------
               foo.x      6156 i/100ms
         Foo.find(1)       732 i/100ms
  Foo.find_by_x(123)       646 i/100ms
-------------------------------------------------
               foo.x    77686.9 (±3.2%) i/s -     393984 in   5.076762s
         Foo.find(1)     7492.2 (±3.3%) i/s -      38064 in   5.086207s
  Foo.find_by_x(123)     6733.8 (±3.2%) i/s -      34238 in   5.090004s

=====> ActiveRecord 3.1.12
Calculating -------------------------------------
               foo.x      1946 i/100ms
         Foo.find(1)       451 i/100ms
  Foo.find_by_x(123)       426 i/100ms
-------------------------------------------------
               foo.x  2496865.6 (±11.7%) i/s -   11421074 in   4.674240s
         Foo.find(1)     6528.8 (±3.6%) i/s -      32923 in   5.049446s
  Foo.find_by_x(123)     6171.4 (±4.3%) i/s -      31098 in   5.048884s

=====> ActiveRecord 3.2.17
Calculating -------------------------------------
               foo.x      1927 i/100ms
         Foo.find(1)       421 i/100ms
  Foo.find_by_x(123)       378 i/100ms
-------------------------------------------------
               foo.x  1651935.2 (±9.8%) i/s -    7771591 in   4.777711s
         Foo.find(1)     6018.6 (±4.0%) i/s -      30312 in   5.044533s
  Foo.find_by_x(123)     5170.5 (±4.1%) i/s -      26082 in   5.053044s

=====> ActiveRecord 4.0.4
Calculating -------------------------------------
               foo.x      1967 i/100ms
         Foo.find(1)       457 i/100ms
  Foo.find_by_x(123)       411 i/100ms
-------------------------------------------------
               foo.x  4237237.5 (±6.2%) i/s -   19009088 in   4.510749s
         Foo.find(1)     6558.9 (±2.9%) i/s -      32904 in   5.021004s
  Foo.find_by_x(123)     5661.9 (±3.1%) i/s -      28359 in   5.013815s

=====> ActiveRecord 4.1.0
Calculating -------------------------------------
               foo.x      1973 i/100ms
         Foo.find(1)       494 i/100ms
  Foo.find_by_x(123)       430 i/100ms
-------------------------------------------------
               foo.x  4066587.9 (±8.7%) i/s -   18214736 in   4.525936s
         Foo.find(1)     7193.6 (±3.1%) i/s -      36062 in   5.018265s
  Foo.find_by_x(123)     6250.0 (±3.1%) i/s -      31390 in   5.027393s