The document discusses various techniques for improving performance in Rails applications, including reducing N+1 queries through eager loading, avoiding extra queries by defining inverse relationships, using view fragment caching by generating cache keys based on model attributes, performing background jobs asynchronously to free up the request thread, and provides exercises for developers to implement these techniques.

1. Performance RailsGirls Advanced Track #3

2. Derek Kraan Software Engineer

3. I've prepared some exercises: git clone git@github.com:derekkraan/railsgirls_performance.git

4. How to increase performance? Do less.

5. N+1 queries

6. N+1 queries • Author.all.each { |author| author.posts } • ActiveRecord will run 1 query to get all authors • and N queries for every author's post.

7. N+1 queries • How to recognize? • Look at the logs.

8. N+1 queries • How to solve? • Eager loading: • Author.includes(:posts).all

9. exercise

10. Extra queries

11. Extra queries • Author.first.blogposts.first.author • This will require 3 queries • Unless you tell ActiveRecord about • the inverse relationship

12. exercise

13. Caching

14. Caching • Many caching strategies • page caching • fragment caching

15. View fragment caching • cache expensive view fragments • <%= cache 'key' do %> • ... • <% end %>

16. View fragment caching • What goes in the key? • Hint: the key must change when • the content within the fragment • changes.

17. View fragment caching • Rails makes a key from AR objects • eg, <%= cache @blogpost do %> • Rails uses @blogpost.cache_key to generate a key • ActiveRecord::Base#cache_key will return • "#{model_name}/#{id}-#{updated_at}"

18. View fragment caching • Or AR relations • <%= cache @blogposts do %> • The key will be a combination of the keys • from the individual blogposts in the collection.

19. Russian doll caching • <% cache @blogposts do %> • <% @blogposts.each do |blogpost| %> • <% cache blogpost do %> • <% end %> • <% end %>

20. Caching • Read more: • http://guides.rubyonrails.org/caching_with_rails.html

21. exercise

22. Background jobs Sidekiq / Resque / DelayedJob

23. Background jobs • Do work out of band • Complete the request faster • The user sees the page faster

24. Background jobs • class Worker • def work • # do work • end • end

25. Background jobs • Worker.perform_async(*args)

26. exercise