mongo_leak_finder.rb

require 'rubygems'
require 'mongo'

class MongoLeakFinder
  def initialize
    db = Mongo::Connection.new.db("cgp")
    @coll = db.collection("records")
    @coll.create_index("n", :unique => true)
  end
  
  MAX = 1_000_000_000
  
  def run
    n = 0
    loop do
      puts "%09i" % n
      @coll.find("n" => n)
      n += 1
      n = 0 if n >= MAX
    end
  end
end

Note: I already have objects in the cgp database with the "n" key.

On my system, this code does not seem to have any space leak. Real memory usage varies between 22.1 MB and 23.1 MB. (Garbage collection apparently kicks in at 23.1 and brings it down to 22.1.)