When a mongo collection is too large for RAM, use cursor this way.

mongoid_cursor.rb

App.db.collection('apps').find({'name' => 'test_name'},{:timeout => false}){|ptr| ptr.each{|x| puts x['user_id']}}

# NOTE in cursor iteration
ptr.each{|x| 
  x.user_id # WRONG
  x['user_id'] # RIGHT
}