DataMapper v. ActiveRecord Performance

Setup

In both apps there is a very basic User model. They are using the same database (on MySQL). The db/seeds.rb file in the DataMapper app creates 10000 user records.

I used the recommended app template to generate the DataMapper app:

rails new dm-perf-app -m http://datamapper.org/templates/rails.rb
bundle install
rails g scaffold User email:string
rake db:setup
rake db:seed

The ActiveRecord app is similar, but uses the same database, so it was less work:

rails new ar-perf-app
bundle install
rails g scaffold User email:string

To test performance, I used variations of:

# DataMapper
env RAILS_ENV=production rails benchmarker "10000.times { |i| u = User.all(:id => i).first; u.email if u }"

# ActiveRecord
env RAILS_ENV=production rails benchmarker "10000.times { |i| u = User.where(:id => i).first; u.email if u }"

... which I stole from Luke Ludwig's "Rails 3 Performance - Not Good Enough article.