Caching strategies in Rails 4

Key-basedcacheexpirationin
Rails4
...or Rails 3 with a dependency
Wednesday, July 31, 13

BuildingBlocks(ActiveRecord::Base)
@product.cache_key
=>“products/1281-20130717091609”
“#{name}/#{id}-#{timestamp}”

BuildingBlocks
(ActionView::Helpers::CacheHelper)
- cache @product do
%h1= @product.name
= image_tag @product.image.url

Write fragment
views/products/1-20130728191246157664000
(“views/#{cache_key}”)
- cache @product do
%h1= @product.name

Youcancomposefragmentkeys,too...
- cache [@product, “reviews”] do
%h1= @product.name
Write fragment
views/products/1-20130728191246157664000/reviews
“views/#{cache_key}/#{extra_args.join(‘/’)}”

“ButwhatifI
change
atemplate?”

Rails.cache.clear

“ButwhatifI
deploy5times
aday”

Justkidding!™

# Gemfile
gem ‘pg’
gem‘cache_digests’
gem ‘haml-rails’
gem ‘cancan’
# ...
(Rails 3 only – built into actionpack 4)

Write fragment
views/products/1-20130728191246157664000/3b2b93d56d331aa7a1bf9267a656d3c9
(“views/#{cache_key}/#{template_digest}”)
- cache @product do
%h1= @product.name
Withcache_digests...
note: template_digest is a digest of the current template and all of it’s dependencies (more on that later)

Cache digest for products/_product.html: 42eb891316f21e68798de5d5aa8021d5
Read fragment
views/products/1-20130728191246157664000/42eb891316f21e68798de5d5aa8021d5
Write fragment
views/products/1-20130728191246157664000/42eb891316f21e68798de5d5aa8021d5
- cache @product do
%h1= @product.name
- # image_tag @product.image.url
...changethetemplate

templatechange
->newdigest
->newfragmentkey
->bustedcache!

Andwedidn’t
havetodo
anything!

“Russiandoll”cachingstrategy
thenotorious

class Product < ActiveRecord::Base
has_many :reviews
end
class Review < ActiveRecord::Base
belongs_to :product, touch: true
end
Product’s cache key now dependent on its reviews

@review.update!(rating: 3)
@review.product’s key gets bumped as well

the “russian doll”...
# products/index.haml
- cache [@products.order(“updated_at ASC”).last, “index”] do
%ul.products
- @products.each do |product|
= render product
# products/_product.haml
- cache product do
%li.product
%h1= product.name
%h2 Reviews!
%ul.reviews
- product.reviews.each do |review|
= render review
# reviews/_review.haml
- cache review do
%li.review
%h4= “#{review.rating} stars!”
%p.content= review.content

the “russian doll”...
index
product
reviews list
review
review
review

@product.reviews.last.update!(rating: 5)
Last review will get re-rendered (and cached)
and container (review list) will get busted -
but when list re-renders all but this last
review can be fetched from cache.

View the template dependency tree...
$ rake cache_digests:nested_dependencies TEMPLATE=your/template/name
ex:
and rake task for Rails 4: https://gist.github.com/nzaillian/6127613

Explicit dependency
If Rails just can’t seem to figure out your dependency you can declare an explicit
dependency in a template by including a comment with a special form:
- # Template Dependency: reviews/summary
(...but you shouldn’t ever have to do this)

OtherResources
https://github.com/rails/cache_digests
http://37signals.com/svn/posts/3113-how-key-based-cache-expiration-works
http://www.youtube.com/watch?v=yhseQP52yIY&t=0:39:39
mustwatch!(DHH’sRailsconf2013outlineofkey-basedcaching)
http://api.rubyonrails.org/classes/ActionView/Helpers/CacheHelper.html

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