First Rails application - Performance & Optimization

Performance: First Rails application

MEDIUM IMPACT

This affects the initial page load speed and server response time when serving the first page of a Rails app.

Serving the home page of a new Rails app

Ruby on Rails

class HomeController < ApplicationController
  def index
    @users = User.limit(10)
  end
end

# View uses simple markup and fragment caching for partials

Limiting database records and caching view fragments reduces server processing and speeds up response.

📈 Performance Gainreduces server response time by 50-70%; improves LCP by loading main content faster

Serving the home page of a new Rails app

Ruby on Rails

class HomeController < ApplicationController
  def index
    @users = User.all
  end
end

# View renders all users with heavy partials and no caching

Loading all users and rendering many partials without caching causes slow response and delays page paint.

📉 Performance Costblocks rendering for 200-500ms depending on user count; triggers multiple database queries and view rendering delays

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Render all database records with heavy partials	High (many nodes)	Multiple reflows due to complex DOM	High paint cost	[X] Bad
Limit records and use fragment caching	Low (few nodes)	Single reflow	Low paint cost	[OK] Good

Rendering Pipeline

Rails processes the request by routing, controller action, database query, view rendering, and then sends HTML to the browser. The browser parses HTML, applies CSS, and paints the page.

→Server Processing

→Network Transfer

→Browser Parsing

→Paint

⚠️ BottleneckServer Processing due to database queries and view rendering

Core Web Vital Affected

LCP

This affects the initial page load speed and server response time when serving the first page of a Rails app.

Optimization Tips

1Limit database queries on initial page load to reduce server processing time.

2Use fragment caching in views to avoid repeated rendering of unchanged content.

3Keep views simple and avoid rendering large numbers of partials on the first page.

Performance Quiz - 3 Questions

What mainly causes slow initial page load in a new Rails app?

A Heavy database queries and complex view rendering

B Too many CSS files loaded

C Large JavaScript bundles only

D Browser caching issues

DevTools: Performance

How to check: Open DevTools > Performance tab > Record while loading the page > Look for long scripting or rendering tasks

What to look for: Long server response time, scripting delays, and large layout or paint times indicate slow Rails app rendering