Increase Rails app performance with Model Caching and Redis

Friday, 22/11/2019

Tram Ho

In Rails applications, we often pay less attention to performance because our data is still small, not enough to slow down the system.

But in some large projects, improving performance becomes very important. The first thing is we will have to eliminate N + 1 queries, after removal is complete and our system is still slow, we need to use Data Cache to optimize.

1. How it works

Model Caching works by using a cache to store data on the first page load. In subsequent visits, the data is only retrieved from the cache, not the query from the DB anymore. Since then our site will improve performance, users will feel our site faster and smoother.

Caching here I use Redis. Because redis is an in-memory data structures store, it stores data structures and key-values in the main memory (RAM). This has made Redis fast processing speed and data recovery almost instantaneously

2. Caching with Redis

2.1 Initializing Project

We will create a small demo application called MyPost as follows:

  rails new MyPost
  rails g scaffold Post content:string

rails new MyPost

rails g scaffold Post content:string

We will use gem “Faker” to fake data

  gem "faker"

1 2	gem "faker"

Then run bundle install and Import the data as follows:

100000.times do
  Post.create(content: Faker::Lorem.paragraph)
end

100000.times do

Post.create(content: Faker::Lorem.paragraph)

end

Here I create 100k records, you can also create smaller. And bh will run the rails db:seed command

Modify the router so that the root page points to our correct Post page

  #routes.rb
  
  root "posts#index"

#routes.rb

root "posts#index"

When the page loads, it will produce the following result

ActiveRecord takes 60.6ms to execute sql statement and Views takes 21941.0ms to display. Thus we can see that our application runs very slowly. Come on, let’s optimize them.

2.2 Initialize Redis

We will install redis via this command

sudo apt-get install redis

1 2	sudo apt-get install redis

Or see the detailed instructions here

After installing redis, we start it

redis-server

1 2	redis-server

To connect Redis to the application, we will have to add some gems to Gemfile , then run bundle install

gem "redis"
gem "redis-namespace"
gem "redis-rails"
gem "redis-rack-cache"

gem "redis"

gem "redis-namespace"

gem "redis-rails"

gem "redis-rack-cache"

2.3 Caching

We reinstall the application.rb file to be able to cache the application with redis

module MyPost
  class Application &lt; Rails::Application
    [...]
    config.cache_store = :redis_store, 'redis://localhost:6379/0/cache', {expires_in: 90.minutes}
    [...]
  end
end

module MyPost

class Application < Rails::Application

[...]

config.cache_store = :redis_store, 'redis://localhost:6379/0/cache', {expires_in: 90.minutes}

[...]

end

We need to create a Redis instance so we can call it anywhere in the Rails application

#initializers/redis.rb

$redis = Redis::Namespace.new "demo-redis", redis: Redis.new

#initializers/redis.rb

$redis = Redis::Namespace.new "demo-redis", redis: Redis.new

We will modify the index method in posts_controller.rb as follows:

# posts_controller.rb

  def index
    @posts = fetch_post
    
    respond_to do |format|
      format.json {render json: @posts, status: :ok}
    end
  end
  
  private
  
  def fetch_post
      posts = $redis.get "posts"

      if posts.nil?
        posts = Post.all.to_json
        $redis.set "posts", posts
      end
      
      JSON.load posts
   end

# posts_controller.rb

def index

@posts = fetch_post

respond_to do |format|

format.json {render json: @posts, status: :ok}

end

private

def fetch_post

posts = $redis.get "posts"

if posts.nil?

posts = Post.all.to_json

$redis.set "posts", posts

end

JSON.load posts

end

Let’s run again and see what results

We see Views only takes 13ms to display and ActiveRecord is 0ms, so the server does not take time to query data, instead of taking data from Redis so our application runs very fast.

3. Some notes

3.1 Handling when redis error

We need to catch exceptions for cases like this

   # posts_controller.rb
   
   def fetch_post
      begin
        posts = $redis.get "posts"

        if posts.nil?
          posts = Post.all.to_json
          $redis.set "posts", posts
        end
        posts = JSON.load posts
      rescue =&gt; error
        puts error.inspect
        posts = Post.all
      end
      posts
   end

# posts_controller.rb

def fetch_post

begin

posts = $redis.get "posts"

if posts.nil?

posts = Post.all.to_json

$redis.set "posts", posts

end

posts = JSON.load posts

rescue => error

puts error.inspect

posts = Post.all

end

posts

end

3.2 Data after update or delete

In case the data after updating or deleting, the data in redis has not been updated yet. So we need to update the data in redis when this is the case

    #Post.rb
    
    class Post &lt; ApplicationRecord
      after_save :clear_cache

      private
      def clear_cache
        $redis.del "posts"
      end
    end

#Post.rb

class Post < ApplicationRecord

after_save :clear_cache

private

def clear_cache

$redis.del "posts"

end

Caching is a great technique to increase the performance of our application. Hope the article will help you have a look at caching

Refer

http://www.victorareba.com/tutorials/speed-your-rails-app-with-model-caching-using-redis https://www.sitepoint.com/rails-model-caching-redis/

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Source : Viblo