Compare MD5 digest vs last modified time (mtime) for file tracking

freshness.rb

#!/usr/bin/env ruby
require 'benchmark/ips'
require 'digest'

PATH = 'jquery.js'.freeze
FILE = File.new(PATH)

Benchmark.ips do |x|
  x.report('mtime')  { FILE.mtime.utc.to_i }
  x.report('digest') { Digest::MD5.file(PATH).hexdigest }
  x.compare!
end

__END__
Results:

  Warming up --------------------------------------
               mtime    48.278k i/100ms
              digest   209.000  i/100ms
  Calculating -------------------------------------
               mtime    574.006k (± 4.8%) i/s -      2.897M in   5.059809s
              digest      2.108k (± 2.5%) i/s -     10.659k in   5.059393s

  Comparison:
               mtime:   574006.2 i/s
              digest:     2108.1 i/s - 272.29x slower

Ruby:

    ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]

Hardware:

    Hardware Overview:

      Model Name: MacBook Pro
      Model Identifier: MacBookPro12,1
      Processor Name: Intel Core i7
      Processor Speed: 3.1 GHz
      Number of Processors: 1
      Total Number of Cores: 2
      L2 Cache (per Core): 256 KB
      L3 Cache: 4 MB
      Memory: 16 GB
      Boot ROM Version: MBP121.0167.B16
      SMC Version (system): 2.28f7

Software:

    System Software Overview:

      System Version: OS X 10.11.5 (15F34)
      Kernel Version: Darwin 15.5.0
      Time since boot: 44 days 1:06