Ruby snippet to test the fastest method of generating alphanumeric strings.

random.rb

require 'benchmark'

n = 10_000_000

puts "\nGenerating random string of length #{n}:"

Benchmark.bm(9) do |x|
  x.report('Method 1: ') do
    range = [('a'..'z'),('A'..'Z'),('0'..'9')].map{ |i| i.to_a }.flatten
    (0...n).map{ range[rand(range.length)] }.join
  end

  x.report('Method 2: ') do
    range = [('a'..'z'),('A'..'Z'),('0'..'9')].map{ |i| i.to_a }.flatten
    (0...n).map{ range.sample }.join
  end

  x.report('Method 3: ') do
    range = [*'0'..'9',*'A'..'Z',*'a'..'z']
    Array.new(n){ range.sample }.join
  end

  x.report('Method 4: ') do
    range = [*'0'..'9',*'A'..'Z',*'a'..'z']
    (0...n).map{ range.sample }.join
  end

  x.report('Method 5: ') do
    range = ((48..57).to_a+(65..90).to_a+(97..122).to_a).map{ |i| i.chr }
    Array.new(n){ range.sample }.join
  end
end