Test of memory usage when creating a lot of slices of a large array.

mem.output

# I'm guessing that MRI and JRuby don't copy the array elements 
# when making a slice, they just reference the original copy with 
# new index bounds.  

$ rvm use ruby-1.9.3-p286
Using /Users/jim/.rvm/gems/ruby-1.9.3-p286
$ ruby mem.rb 
Before: 12716
After: 12744

$ rvm use jruby
Using /Users/jim/.rvm/gems/jruby-1.7.3
$ ruby mem.rb 
Before: 95556
After: 95780

# However, it does look like Rubinius does copy
# the actual array elements.

$ rvm use rbx
Using /Users/jim/.rvm/gems/rbx-head
$ 
$ ruby mem.rb 
Before: 36824
After: 856120

mem.rb

def mem_usage
  process_id = $$.to_s
  lines = `ps -v`.split(/\n/)
  lines.each do |line|
    fields = line.split
    if fields[0] == process_id
      return fields[7].to_i
    end
  end
  0
end

kb = 1024
mb = kb*kb
a = Array.new(mb)
puts "Before: #{mem_usage}"
slices = (1..100).map { |i| a[i..-1] }
puts "After: #{mem_usage}"