hash_smash.rb

def hash_smash bench_size, bm
  hash_1 = {}
  hash_2 = {}

  1.upto(bench_size) do |n|
    k = "val#{n}"
    hash_1[k] = {
      name: k,
      total: n * 2,
    }
  end

  h1 = hash_1["val500"][:total]

  1.upto(bench_size) do |n|
    k = "val#{n}"
    hash_2[k] = {
      name: k,
      total: n * 3,
    }
  end

  h2 = hash_2["val500"][:total]

    bm.report(bench_size) do
      hash_1.each do |k, v|
        v[:total] += hash_2[k][:total]
      end
    end

  h3 = hash_1["val500"][:total]

  abort "oops this is wrong" unless h3 == h1 + h2
end

require 'benchmark'

Benchmark.bm(10) do |bm|
  hash_smash 2_000, bm
  hash_smash 20_000, bm
  hash_smash 200_000, bm
  hash_smash 2_000_000, bm
end
__END__
                 user     system      total        real
2000         0.000000   0.000000   0.000000 (  0.000832)
20000        0.020000   0.000000   0.020000 (  0.015878)
200000       0.200000   0.000000   0.200000 (  0.197828)
2000000      2.770000   0.040000   2.810000 (  2.818214)