Ruby2.0の新機能、lazyを調査中。

lazy_demo.rb

# Benchmark of Enumerable#lazy.
# 'production.log' is a log of Rails application that size is 43.6MB.

require 'benchmark'

Benchmark.bm do |x|
  x.report('normal') do
    100.times do
      File.open("./production.log") do |f|
        f.each_line.select { |line| line =~ /RoutingError/ }.first(10)
      end
    end
  end

  x.report('with lazy') do
    100.times do
      File.open("./production.log") do |f|
        f.each_line.lazy.select { |line| line =~ /RoutingError/ }.first(10)
      end
    end
  end
end

#   user     system      total        real
# non lazy 201.990000  18.420000 220.410000 (229.605248)
# with lazy  0.140000   0.020000   0.160000 (  0.169942)
# [Finished in 230.0s]


# sample.logは各行に1~20までの数字が入っているだけのファイル。

# not lazy
File.open("./sample.log") do |f|
  puts f.each_line.map(&:to_i).select{|x| x % 2 == 0}.first(3)
end
# map method returns an Array object like following.
# [1,2,3,...20]

# lazy
File.open("./sample.log") do |f|
  puts f.each_line.lazy.map(&:to_i).select{|x| x % 2 == 0}.first(3)
end

ちなみに似たようなやつを10000万回まわしたら1.9.3だと2時間強かかった。

                             user     system       total         real

Ruby2.0.0 p-0 with lazy 17.540000 1.390000 18.930000 ( 19.041330)

Ruby1.9.3 p-125 7661.230000 238.900000 7900.130000 (8324.068630)