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Rails CachingAlexandru Keszeg

(Software Developer @ PITECH+PLUS)

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This is Rails, how hard can it be?

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This is Rails, how hard can it be?<% cache @user do %> <%= render partial: 'user' %><% end %>

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Thank you for your time

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TOPICS

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TOPICS

WHY?

fragment caching

SQL caching

HTTP Caching

expiration

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WHY?

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WHY?

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Fragment Cachingcache small pieces of information instead of full pages

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1. Do not expire keys

2. Model associations govern expiry

3. Nested caching is best

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Do not expire keys

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cache_key

user = User.first

=> User id: 1, updated_at: "2014-10-02 18:12:57"

user.cache_key

=> users/1-20141002181257446781000

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cache_key

user = User.first

=> User id: 1 , updated_at: "2014-10-02 18:12:57"

user.cache_key

=> users/1-20141002181257446781000

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<% cache @user do %> <%= render partial: 'user' %><% end %>

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<% cache @user do %> <%= render partial: 'user' %><% end %>

First time we load the pageRead fragment views/users/1-20141002181257446781000/ 95a652b13f0fc5b7bc8785ac31b6b8b9 (1.2ms)Write fragment views/users/1-20141002181257446781000/ 95a652b13f0fc5b7bc8785ac31b6b8b9 (1.2ms)

All other page loads:Read fragment views/users/1-20141002181257446781000/ 95a652b13f0fc5b7bc8785ac31b6b8b9 (1.2ms)

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Model associations govern expiry

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class Project has_many :todo_lists

class TodoList belongs_to :project, touch: true has_many :todos

class Todo belongs_to :todo_list, touch: true

when something changes, its direct parent is also changed

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Nested caching is best

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- @projects.each do |project| - cache ['project', project] do ...project - project.todo_lists.each do |todo_list| - cache ['todo_list', todo_list] do ...todo list - todo_list.todos.each do |todo_list| - cache ['todo', todo] do ...todo

when something changes, we don't have to regenerate the entirepage

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Before Rails4

- @projects.each do |project| - cache ['v1', 'project', project] do

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Rails 4 solves this problem with cache digests.

A call to #cache in your views will now suffix a digest of the template and itsdependencies. No longer will you need to worry about fragment cachedependencies and versioning!

user.cache_key=> users/1-20141002181257446781000

Read fragment views/users/1-20141002181257446781000/ 95a652b13f0fc5b7bc8785ac31b6b8b9 (1.2ms)

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Rails 4 solves this problem with cache digests.

A call to #cache in your views will now suffix a digest of the template and itsdependencies. No longer will you need to worry about fragment cachedependencies and versioning!

user.cache_key=> users/1-20141002181257446781000

Read fragment views/users/1-20141002181257446781000/ 95a652b13f0fc5b7bc8785ac31b6b8b9 (1.2ms)

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Rails 4 solves this problem with cache digests.

A call to #cache in your views will now suffix a digest of the template and itsdependencies. No longer will you need to worry about fragment cachedependencies and versioning!

user.cache_key=> users/1-20141002181257446781000

Read fragment views/users/1-20141002181257446781000/ 95a652b13f0fc5b7bc8785ac31b6b8b9 (1.2ms)

There's a gem for that

rails/cache_digests

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Exercise

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Perspective data

Or how to make your cache useless

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Consider the impact of a single button

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.col-sm-12.no-lr-padding.ticket-info .col-price-block %span.top-line From %span.ticket-price.bottom-line = formated_cheapest_ticket_price(activity) .col-tickets-left-block - unless activity.hide_remaining_tickets? %span.color-default.top-line Tickets left: %span.bottom-line = activity_tickets_left(activity) .col-attendees-block %span.top-line Attendees: %span.bottom-line = activity_attendees_count(activity)

.user-buttons-block %a.btn.btn-wishlist.btn-85 %span.event_wishlist_span = wishlisted_label(activity, current_user)

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hit rate?cache ['event', event] do

turns into:

cache ['event', event, current_user] do

Hit rate: 1 / Event.count * User.count

*probably should avoid

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Solutions

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Solutions

Move it client side

.event-pod{data- wishlisted="#{wishlisted_label(activity, current_user)}"}

$('.event-pod').each(function(){ $(this).find('.wishlisted_button').html( $(this.data('wishlisted')) );})

???

This is good if you want to decouple the usere data or generate it in

Also good for edge caching.*extra complexity

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There's gem for that!

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neighborland/cache_rocket

= render_cached 'outer', replace: 'inner'

outer.html.haml

- cache 'outer' do .lots .of .htmls = cache_replace_key 'inner'

inner.html.haml

= uncacheable_content

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benefits

cache more stuff

more hits

faster pages

less stuff in cache

more hits

less RAM used

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The fastest code is no code

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The fastest code is no code

Leverage the browser cache

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def show @article = Article.find(params[:id])

if stale?(:etag => @article, :last_modified => @article.created_at.utc) @statistics = @article.really_expensive_call respond_to do |format| # all the supported formats end endend

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def show @article = Article.find(params[:id])

if stale?(:etag => @article, :last_modified => @article.created_at.utc) @statistics = @article.really_expensive_call respond_to do |format| # all the supported formats end endend

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def show @article = Article.find(params[:id])

if stale?(:etag => @article, :last_modified => @article.created_at.utc) @statistics = @article.really_expensive_call respond_to do |format| # all the supported formats end endend

=> "304 Not Modified"

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Edge cachingCloudfront

Akamai

fastly

Varnish...

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Follow these rules

everything common is served in the initial request

perspective data done with js in a different http request

expiration is handled by HTTP headers

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Cache-Control: public - Any cache can store a copy of the content.

Cache-Control: private - Don't store, this is for a single user.

Cache-Control: no-cache - Re-validate before serving this content.

Cache-Control: no-store - Don't store this content. Ever. At all. Please.

Cache-Control: public, max-age=[seconds] - Caches can store this content for nseconds.

Cache-Control: s-maxage=[seconds] - Same as max-age but applies specificallyto proxy

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What about my models?

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class SuggestionsController def show @users = Rails.cache.fetch(['users', params['page']]) do # we need to call .all to hit the database otherwise # we cache only the ruby query object User.suggestions.page(params['page']).all end endend

*all is for rails3

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How do i expire that?

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How do i expire that?

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There's a gem for thatahawkins/cashier

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Tag based cachingInstead of using updated_at to cause a cache miss, record where your objectsare cached

cache @something, tag: ['dashboard', 'settings']

@users = Rails.cache.fetch(['users', params['page']], tag: 'users') do # we need to call .all to hit the database otherwise # we cache only the ruby query object User.suggestions.page(params['page']).allend

...

User#after_commit...

Cashier.expire "users"

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But i want hourly updates on my homepage,oh please will you help me?

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But i want hourly updates on my homepage,oh please will you help me?

cache 'homepage', expires_in: 1.hour do

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This thing doesn't update, i want a buttonto nuke everything!

class NukesController

def create expire_fragment('homepage'); end

end

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How well is it working for us?

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Where to go from here?

Caching with Rails: An overview

IdentityCache

Multi-fetch Fragments

SecondLevelCache

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Thank you

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