performance comparison of Mongoid, Moped and `mongo` shell w/ MongoDB 2.4.3

mongo_shell.js

function bench(f) {
  var start = new Date();
  f();
  var finish = new Date();
  print( ((finish-start) / 1000) + 's' );
}

bench(function(){
  db.users.find().limit(2000).forEach(function(user){

  });
});

// 2.859s

mongoid_and_moped.rb

require 'benchmark'

num_records = 2000

# Mongoid
puts Benchmark.measure {
  User.limit(num_records).each do |user|

  end
}
#   0.510000   0.070000   0.580000 (  0.665689)

# Moped
puts Benchmark.measure {
  User.collection.find().limit(num_records).each do |user|

  end
}
#   0.480000   0.030000   0.510000 (  0.555456)

If the first is running in the shell it's copying the data over as well from server to client.