This document discusses different caching techniques in Rails including model-level caching using Rails.cache.fetch and Rails.cache.delete, fragment caching using cache blocks, and HTTP caching using etags, fresh_when, and expires_in to control caching. It recommends using Memcached as a cache server with the Dalli gem and provides an overview of configuring caching in Rails and implementing the different caching strategies.

1. Caching in Rails
Vysakh Sreenivasan

2. Only 2 hard
Problems in CS
● Naming
● Cache invalidation

3. Caching in a web app
● Prevent hitting databases.
● Cache the html responses.
● Help browser implement caching.

4. Before implementing caching
we need a cache server

5. Memcached is the popular cache server
sudo apt-get install memcached

6. Before implementing caching in
Rails we need to configure

7. config.action_controller.perform_caching = true

8. Using memcached with Rails 4.0
● gem ‘dalli’
● config.cache_store = :mem_cache_store

9. Lets get to the implementation

10. #1 Model level caching

11. Rails.cache.fetch
● First time, it can’t fetch a cache, so it will write a cache.
● Then it reads those caches.

12. Rails.cache.delete
● When passed an argument, it deletes the specific cache.
● You can clear caches in hooks like after_save

13. You can also use this to cache API results

14. #2 Fragment caching

15. <% cache @post do %>
<h3> <%= @post.title %> </h3>
<% end %>
cache_key: views/posts/1-
201505056193031061005000/bea67108094918eeba42cd4a6e786901
based on @post.cache_key
which is based on updated_at
md5 hash based on the view’s contents

16. Cache key changes when
● the record is updated -> a new cache_key is formed
● the view is changed -> a new md5 key is generated
The old keys will be there, which will be removed
automatically by memcached

17. #3 http caching

18. e-tag & 304 not modified

19. fresh_when(@post)
# or
fresh_when(etag: @post , last_modified: @post.updated_at)
based on @post.cache_key
which is based on updated_at

20. if stale?(@post)
respond_to do |f|
…
end
end
Alternate syntax. Especially when using respond_to

21. def show
@post = Post.first
expires_in 5.minutes
end
Cache control: max_age

22. Recap
1 Model level
● Rails.cache.fetch
● Rails.cache.delete
2 Fragment
<% cache @post do %>
<% end %>
3. etags
if stale?(@post)

23. Resources
● Docs: http://guides.rubyonrails.org/caching_with_rails.html
● Railscasts episodes on http caching, low level caching,
cache digests, dalli gem.