This document provides an overview of various topics related to optimizing performance in Ruby on Rails web applications, including: - Different Rails application servers like Passenger, Unicorn, and Puma. - Factors that affect web request performance like redirects, DNS lookups, and front-end loading. - Database performance issues like N+1 queries and missing indexes that can be addressed through eager loading and adding indexes. - Using caching at different levels like page, action, and fragment caching as well as ensuring caches are expired properly. - Using background job queues like Resque to process long-running tasks asynchronously. - The importance of monitoring applications and addressing performance issues that

1. Intro to Rails #webperf

3. teu rhu man
@ ama

4. ruby -v
1.9.2
1.8.7
1.9.3
1.8.6

5. require ‘benchmark’
MRI 1.9.3
MRI 1.8.7
RBX 1.2.4
JRuby 1.6.7

6. Passengers,
Unicorns,
Pumas.
Oh my!

7. Passenger
Simple to operate.
Simple configuration.
Handles worker management.
Great for multi-app environments.
Great for low resource environments.
Attached to Nginx/Apache HTTPD.

8. Unicorn
Highly configurable.
Independent of front-end web server.
Master will reap children on timeout.
Great for single app environments.
Allows for zero downtime deploys.

9. Puma
Based on Mongrel.
Designed for concurrency.
Uses real threads.

10. Anatomy of a Web Request

11. Link Clicked DOM Loaded
Redirects Cache DNS TCP SSL Request App Response DOM Render
First Byte Load

12. 80% in Front-End

13. Inside the Web App

14. Database Performance

15. Lazy Loading
๏ ORMs make it easy to access data.
๏ Easy access to data can create issues.
๏ Performance issues are hard to see in
development mode.
๏ Look to production metrics to optimize
and refactor.

16. N+1 Query Creep
# app/models/customer.rb
class Customer < ActiveRecord::Base
has_many :addresses
end
# app/models/address.rb
class Address < ActiveRecord::Base
belongs_to :customer
end
# app/controllers/customers_controller.rb
class CustomersController < ApplicationController
def index
@customers = Customer.all
end
end
# app/views/customers/index.html.erb
<% @customers.each do |customer| %>
<%= content_tag :h1, customer.name %>
<% end %>

17. N+1 Query Creep
# app/views/customers/index.html.erb
<% @customers.each do |customer| %>
<%= content_tag :h1, customer.name %>
<%= content_tag :h2, customer.addresses.first.city %>
<% end %>
If @customers has 100 records, you'll have 101 queries:
SELECT "customers".* FROM "customers"
SELECT "addresses".* FROM "addresses" WHERE "addresses"."customer_id" = 1 AND
"addresses"."primary" = 't' LIMIT 1
SELECT "addresses".* FROM "addresses" WHERE "addresses"."customer_id" = 2 AND
"addresses"."primary" = 't' LIMIT 1
SELECT "addresses".* FROM "addresses" WHERE "addresses"."customer_id" = 3 AND
"addresses"."primary" = 't' LIMIT 1
...
...
SELECT "addresses".* FROM "addresses" WHERE "addresses"."customer_id" = 100
AND "addresses"."primary" = 't' LIMIT 1

18. Eager Load Instead
# app/controllers/customers_controller.rb
class CustomersController < ApplicationController
def index
@customers = Customer.includes(:addresses).all
end
end
If @customers has 100 records, now we only have 2 queries:
SELECT "customers".* FROM "customers"
SELECT "addresses".* FROM "addresses" WHERE "addresses"."customer_id" IN (1,
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,
23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41,
42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60,
61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98,
99, 100)

19. Finding N+1

20. Missing Indexes
๏ Searching a 1,000 row table with an
index is 100x faster than searching
without.
๏ Put indexes anywhere you might need to
query; less is not more with indexes.
๏ Writing an index will lock your tables.

21. Missing Indexes Hurt

22. Indexes are Easy
# db/migrate/20120201040247_add_index_for_shop_id_on_orders.rb
class AddIndexForShopIdOnOrders < ActiveRecord::Migration
def change
add_index :orders, :shop_id
end
end

23. Cache All The Things

24. Page Caching
# app/controllers/products_controller.rb
class ProductsController < ActionController
caches_page :index
def index
@products = Products.all
end
def create
expire_page :action => :index
end
end
# /opt/nginx/conf/nginx.conf
location / {
gzip_static on;
}

25. Action Caching
# app/controllers/products_controller.rb
class ProductsController < ActionController
before_filter :authenticate
caches_action :index
def index
@products = Product.all
end
def create
expire_action :action => :index
end
end

26. Fragment Caching
# app/views/products/index.html.erb
<% Order.find_recent.each do |o| %>
<%= o.buyer.name %> bought <%= o.product.name %>
<% end %>
<% cache(‘all_products’) do %>
All available products:
<% Product.all.each do |p| %>
<%= link_to p.name, product_url(p) %>
<% end %>
<% end %>
# app/controllers/products_controller.rb
class ProductsController < ActionController
def update
expire_fragment(‘all_products’)
end
end

27. Expiring Caches
is Hard

28. Russian Doll Caching
# app/views/products/show.html.erb
<% cache product do %>
Product options:
<%= render product.options %>
<% end %>
# app/views/options/_option.html.erb
<% cache option do %>
<%= option.name %>
<%= option.description %>
<% end %>
# app/models/product.rb
class Product < ActiveRecord::Base
has_many :options
end
# app/models/option.rb
class Option < ActiveRecord::Base
belongs_to :product, touch: true
end

29. Background Jobs

30. Procrastinate
Reporting.
Sending email.
Processing images.
Call external services.
Building & Expiring Caches.

31. Rescued by Resque
class ReferralProcessor
@queue = :referrals_queue
def self.perform(schema_name, order_item_id)
order_item = OrderItem.find(order_item_id)
order = order_item.order
user = order.user
credit = AccountCredit.credit(order_item.unit_price, user, 'referral')
credit.message = I18n.t('account_credits.predefined_messages.referral',
:description => order_item.description)
credit.save!
debit = Transaction.account_debit(credit.amount, user)
debit.order = order
debit.save!
order.issue_refund(return_to_inventory: false, gateway_first: true,
cancel_items: false, cancel_certificates: false,
amount: credit.amount, as: 'original', notify_user: false)
if user.receives_mail_for?(:referral_purchase)
SystemMailer.referral_refund(order_item, credit).deliver
end
end
end

32. Get in Line
class ReferralObserver < ActiveRecord::Observer
def after_create(referral)
Resque.enqueue_in(1.day, ReferralProcessor, referral.item.id)
end
end
# Get it started
$ PIDFILE=./resque.pid
BACKGROUND=yes
QUEUE=referrals_queue
rake environment resque:work

33. It’s Free in Rails 4
Establishing basic Queue API.
Implement push and pop.
Easily swap out for Resque, Sidekiq,
Delayed job.

34. What’s One More Second?

35. 7%
Fewer Conversions

36. 11%
Fewer Page Views

37. Time is
Money

38. Monitor your applications.
Performance is not set it and forget it.
Database indexes are cheap, make more.
Cache something, somewhere.
Push work off to the background.
Don’t neglect front-end performance.

39. Q?
30-day free trial at
newrelic.com/30