Performance Comparison

performance.rb

# plain ActiveRecord
Benchmark.measure do
  User.where(:activated => true).limit(200000).map(&:first_name)
end
# =>  58.210000  12.970000  71.180000 ( 73.134415)

# writing the improved SQL by hand
Benchmark.measure do
  ActiveRecord::Base.connection.select_all("select * from users where activated = 1 limit 200000").map { |attrs| attrs[:first_name] }
end
# =>  45.910000  12.850000  58.760000 ( 60.632703)
# better performance but ugly as sin

# Using Arel and find_as_hashes
Benchmark.measure do
  User.where(:activated => true).limit(200000).all_as_hashes.map { |attrs| attrs[:first_name] }
end
# =>  45.950000  13.040000  58.990000 ( 60.826395)
# ah, the improved performance with the benefit of Arel