Rails Optimization

Write code that makes it work first

Then (if needed) optimize

DB Indexes

class AddIndexesToTables < ActiveRecord::Migration
  def change
    add_index :authors_posts, :post_id
    add_index :authors_posts, :author_id
    add_index :content_references, :site_block_id
    add_index :content_references, :post_id
    add_index :posts, :category_id
    add_index :posts, :author_id
  end
end

Querying Tips

Vanilla Rails will take you a long way. But in every app, there are places where speed is a big deal. And when you find those places, reducing SQL calls is an easy place to start optimizing." -@justinweiss

source: https://blog.codeship.com/speed-up-activerecord/

Check Server Logs

Avoid this:

Processing by RestaurantsController#index as HTML
  Restaurant Load (1.6ms)  SELECT `restaurants`.* FROM `restaurants`
  Review Load (1.2ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 1
  Review Load (1.2ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 2
  Review Load (1.1ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 3
  Review Load (1.2ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 4
  Review Load (1.2ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 5
  Review Load (1.2ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 6
  Review Load (1.2ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 7
  Review Load (1.0ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 8
  Review Load (1.0ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 9
  Review Load (1.0ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` = 10

Go for this:

Restaurant Load (1.2ms)  SELECT `restaurants`.* FROM `restaurants`
Review Load (3.0ms)  SELECT `reviews`.* FROM `reviews` WHERE `reviews`.`restaurant_id` IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

@restaurants = Restaurant.all.includes(:reviews)

@restaurants = Restaurant.all
@restaurants.each do |thing|
  "#{thing.review}"

n+1

- Stay away from n+1 with eager loading

- When you need optimization and don't care how you get your data, use more sql and less rails helpers

.find_by_sql()

.includes()

Using #blank? vs #empty? on an ActiveRecord Relation

User.where(screen_name: ['user1','user2']).blank?

behind the scenes:

1. Query the database for all user data

2. Load the users into an array

3. Check to see if the array size is zero

SELECT "users".* FROM "users" WHERE "users"."screen_name" IN ('user1','user2')

[<#User:0x007fbf6413c510>,<#User:0x007fbf65ab1c70>]

=> true

#blank?

source: http://hashrocket.com/blog/posts/rails-quick-tips-easy-activerecord-optimizations

#empty?

User.where(screen_name: ['user1','user2']).empty?

1. Query database for ONLY a count

SELECT COUNT(*) FROM "users" WHERE "users"."screen_name" IN ('user1','user2')

2. Check to see if the count is zero

=> true

behind the scenes:

So #blank? will load the entire array, then check to see if that array is empty. On the other hand, #empty? asks the db for a count, and checks to see if that number is zero.

#map vs #pluck on an ActiveRecord Relation

#map

User.where(email: ['jane@example.com', 'john@example.com']).map(&:screen_name)

behind the scenes:

1. Query the db for all user data

SELECT "users".* FROM "users" WHERE "users"."email" IN ('jane@example.com','john@example.com')

2. Load users into an array

[<#User:0x007fbf6413c510>,<#User:0x007fbf65ab1c70>]

3. Iterate over array to collect screen_names

['user1','user2']

#pluck

User.where(email: ['jane@example.com', 'john@example.com']).pluck(:screen_name)

behind the scenes:

1. Query the db for ONLY screen_names

SELECT "users"."screen_name" FROM "users"

WHERE "users"."email" IN ('jane@example.com','john@example.com')

2. Return those screen_names in an array

['user1','user2']

So #map will load an entire array, then iterate to collect the screen_names. Alternatively, #pluck asks the database for exactly what it needs and returns an array of just those items.

Caveat

Don't use #pluck if you're passing in a #where

emails =  ['jane@example.com', 'john@example.com']
User.where(screen_name: User.where(email: emails).pluck(:screen_name)).empty?

(using #pluck with #where)

1. Query for just the emails

SELECT "users"."email" FROM "users" WHERE "users"."email" IN ('jane@example.com','john@example.com')

2. Query for the count

SELECT COUNT(*) FROM "users" WHERE "users"."screen_name" IN ('user1','user2')

3. Check if the count is zero

=> true

Instead use #select with a #where

emails =  ['jane@example.com', 'john@example.com']
User.where(screen_name: User.where(email: emails).select(:screen_name)).empty?

1. Make one query for count with subquery

SELECT COUNT(*) FROM "users" WHERE "users"."screen_name" IN (
     SELECT "users"."screen_name" FROM "users" WHERE "users"."email"
        IN ('jane@example.com','john@example.com')
)

2. Check if the count is zero

=> true

Recap

1. Use #empty? or #any? instead of #blank or #present?

2. Never use #map on active record relations, use #pluck instead

3. If you're using #pluck to pass values to a #where, use #select instead

On ActiveRecord Associations:

Browser Caching

-Phil Karlton

ETags vs Last Modified/If Modified Since Headers

http://blog.pixelastic.com/

Cache Invalidation

Don't do it.

We have control over invalidating the client's cache. All we have to do is change the filename and the browser/server knows that the old file doesn't exist anymore and the new one should be downloaded.