Rails #33954 benchmarks

rails-33954-benchmarks.md

Link to original PR

Test code

I ran the following code to benchmark on my local machine:

require 'benchmark'
require 'benchmark/memory'

class OldTest
  # NOTE: the code in this class was originally written by @febeling here: 
  # https://github.com/rails/rails/pull/33954/commits/76f9b5ece6ad833351275445ab9f9d1c886dc293#diff-faefed8fb304ae45721a2645df0e1789R166

  def difference(a, b)
    set_a = as_set(a)
    set_b = as_set(b)

    from_set(set_a - set_b)
  end

  def intersection(a, b)
    set_a = as_set(a)
    set_b = as_set(b)

    from_set(set_a & set_b)
  end

  def as_set(records)
    records.zip(occurrences(records))
  end

  def from_set(record_set)
    record_set.map(&:first)
  end

  def occurrences(array)
    counts = Hash.new(0)

    array.map do |object|
      counts[object] += 1
    end
  end
end

class NewTest
  def difference(a, b)
    set_b = occurrences(b)

    a.reject do |object|
      occurrence?(set_b, object)
    end
  end

  def intersection(a, b)
    set_b = occurrences(b)

    a.select do |object|
      occurrence?(set_b, object)
    end
  end

  def occurrences(array)
    array.each_with_object(Hash.new(0)) do |object, counts|
      counts[object] += 1
    end
  end

  def occurrence?(set, object)
    set[object] > 0 && set[object] -= 1
  end
end


old_test = OldTest.new
new_test = NewTest.new

c = [1, 2, 2, 2, 3, 4, 4, 4, 4, 4, 5, 5, 4, 2, 2, 3]
d = [3, 3, 3, 4, 4, 5, 5, 6, 3, 3, 3, 3, 7, 3, 7, 7]
n = 150_000_000
one_hundred = 100
ten_thousand = 10_000

puts "\n-------------------- DIFFERENCE --------------------\n"

Benchmark.bmbm do |x|
  x.report('NEW') { new_test.difference(c, d) * n }
  x.report('OLD') { old_test.difference(c, d) * n }
end

puts "\n-------------------- INTERSECTION --------------------\n"

Benchmark.bmbm do |x|
  x.report('NEW') { new_test.intersection(c, d) * n }
  x.report('OLD') { old_test.intersection(c, d) * n }
end

puts "\n-------------------- MEMORY --------------------\n"

puts "\n-------- 10,000x array size\n"

Benchmark.memory do |x|
  x.report('NEW (difference)') { new_test.difference(c * ten_thousand, d * ten_thousand) }
  x.report('OLD (difference)') { old_test.difference(c * ten_thousand, d * ten_thousand) }

  x.compare!
end

Benchmark.memory do |x|
  x.report('NEW (intersection)') { new_test.difference(c * ten_thousand, d * ten_thousand) }
  x.report('OLD (intersection)') { old_test.difference(c * ten_thousand, d * ten_thousand) }

  x.compare!
end

puts "\n-------- 100x array size\n"

Benchmark.memory do |x|
  x.report('NEW (difference)') { new_test.difference(c * one_hundred, d * one_hundred) }
  x.report('OLD (difference)') { old_test.difference(c * one_hundred, d * one_hundred) }

  x.compare!
end


Benchmark.memory do |x|
  x.report('NEW (intersection)') { new_test.intersection(c * one_hundred, d * one_hundred) }
  x.report('OLD (intersection)') { old_test.intersection(c * one_hundred, d * one_hundred) }

  x.compare!
end

Results

-------------------- DIFFERENCE --------------------

Rehearsal ---------------------------------------
NEW   4.930000   8.080000  13.010000 ( 14.493172)
OLD   5.190000   9.570000  14.760000 ( 16.182891)
----------------------------- total: 27.770000sec

          user     system      total        real
NEW   4.050000   3.650000   7.700000 (  8.085193)
OLD   4.000000   3.530000   7.530000 (  7.799358)

-------------------- INTERSECTION --------------------

Rehearsal ---------------------------------------
NEW   2.950000   4.670000   7.620000 (  8.145647)
OLD   2.550000   3.380000   5.930000 (  6.247103)
----------------------------- total: 13.550000sec

          user     system      total        real
NEW   2.080000   1.620000   3.700000 (  3.710833)
OLD   2.310000   1.790000   4.100000 (  4.123227)

-------------------- MEMORY --------------------


-------- 10,000x array size

Calculating -------------------------------------
    NEW (difference)     3.582M memsize (     0.000  retained)
                         4.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
    OLD (difference)    19.743M memsize (     0.000  retained)
                       320.012k objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
    NEW (difference):    3581960 allocated
    OLD (difference):   19742528 allocated - 5.51x more
Calculating -------------------------------------
  NEW (intersection)     3.582M memsize (     0.000  retained)
                         4.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
  OLD (intersection)    19.743M memsize (     0.000  retained)
                       320.012k objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
  NEW (intersection):    3581960 allocated
  OLD (intersection):   19742528 allocated - 5.51x more

-------- 100x array size

Calculating -------------------------------------
    NEW (difference)    37.808k memsize (     0.000  retained)
                         4.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
    OLD (difference)   199.976k memsize (     0.000  retained)
                         3.212k objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
    NEW (difference):      37808 allocated
    OLD (difference):     199976 allocated - 5.29x more
Calculating -------------------------------------
  NEW (intersection)    38.808k memsize (     0.000  retained)
                         4.000  objects (     0.000  retained)
                         0.000  strings (     0.000  retained)
  OLD (intersection)   190.216k memsize (     0.000  retained)
                         3.212k objects (     0.000  retained)
                         0.000  strings (     0.000  retained)

Comparison:
  NEW (intersection):      38808 allocated
  OLD (intersection):     190216 allocated - 4.90x more