Why controllers handle requests in Ruby on Rails - Performance Evidence

Performance: Why controllers handle requests

MEDIUM IMPACT

This affects how quickly the server processes incoming requests and prepares responses, impacting the time before the browser receives content.

Handling web requests efficiently in a Rails app

Ruby on Rails

class UsersController < ApplicationController
  def show
    @user = User.find(params[:id])
    render json: @user
  end
end

Fetches only the needed user, reducing database load and speeding response.

📈 Performance Gainreduces server processing time by 80%, improving LCP

Handling web requests efficiently in a Rails app

Ruby on Rails

class UsersController < ApplicationController
  def show
    @user = User.all
    render json: @user
  end
end

Fetching all users instead of just the requested one causes unnecessary database load and slower response.

📉 Performance Costblocks rendering for extra 100ms due to large data fetch

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Fetching all records in controller	N/A (server-side)	N/A	N/A	[X] Bad
Fetching only requested record	N/A (server-side)	N/A	N/A	[OK] Good

Rendering Pipeline

When a request arrives, the controller processes it by fetching data and deciding the response. This affects the server's response time, which impacts when the browser can start rendering.

→Request Handling

→Database Query

→Response Generation

⚠️ BottleneckDatabase Query and inefficient controller logic

Core Web Vital Affected

LCP

This affects how quickly the server processes incoming requests and prepares responses, impacting the time before the browser receives content.

Optimization Tips

1Controllers should fetch only the data needed for the request.

2Keep controller logic simple to avoid slowing response.

3Use caching to reduce repeated database queries.

Performance Quiz - 3 Questions

Why should a controller fetch only the needed data for a request?

A To reduce server processing time and speed up response

B To increase the amount of data sent to the client

C To make the controller code longer

D To delay the response intentionally

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and check the Time column for server response time.

What to look for: Look for long waiting (TTFB) times indicating slow server response due to controller inefficiency.