approx_ruby_memory_usage.rb

def profile(unit = :M)
  # trying to see where our memory is going
  population = Hash.new{|h,k| h[k] = [0,0]}
  array_sizes = Hash.new{|h,k| h[k] = 0}
  ObjectSpace.each_object do |object|
    # rough estimates, see http://eigenclass.org/hiki.rb?ruby+space+overhead
    size = case object 
           when Array
             array_sizes[object.size / 10] += 1
             case object.size
             when 0..16
               20 + 64
             else
               20 + 4 * object.size * 1.5
             end
           when Hash;    40 + 4 * [object.size / 5, 11].max + 16 * object.size
           when String;  30 + object.size
           else 120 # the iv_tbl, etc
           end
    count, tsize = population[object.class] 
    population[object.class] = [count + 1, tsize + size]
  end

  population.sort_by{|k,(c,s)| s}.reverse[0..10].each do |klass, (count, bytes)|
    case unit
    when :M
      puts "%-20s  %7d  %9f" % [klass, count, bytes/1048576]
    when :B
      puts "%-20s  %7d  %9d" % [klass, count, bytes]
    end
  end
end