benchmarking.rb

require "benchmark"

user = User.find_by_name("Teemo")

# See the time it takes to count the comments of a post in an n+1 query
puts Benchmark.realtime { user.posts.each { |post| puts post.comments.count } }

# See the time it takes to count the comments of a post with eager-loading
# Should be faster
puts Benchmark.realtime { user.includes(:posts).posts.each { |post| puts post.comments.count } }