Job creation and queuing in Ruby on Rails - Performance & Optimization

Performance: Job creation and queuing

HIGH IMPACT

This affects page load speed and user interaction responsiveness by offloading heavy tasks to background jobs.

Handling a slow task like sending emails during a web request

Ruby on Rails

def create
  UserMailer.welcome_email(@user).deliver_later
  render :show
end

Queues the email to be sent asynchronously, freeing the web request immediately.

📈 Performance GainNon-blocking request, improves INP by 200-500ms

Handling a slow task like sending emails during a web request

Ruby on Rails

def create
  UserMailer.welcome_email(@user).deliver_now
  render :show
end

Sending email synchronously blocks the web request, delaying response time.

📉 Performance CostBlocks rendering for 200-500ms depending on email server speed

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Synchronous job execution	Minimal	Multiple reflows due to blocking	High paint cost due to delayed rendering	[X] Bad
Asynchronous job queuing	Minimal	Single reflow	Low paint cost, fast rendering	[OK] Good

Rendering Pipeline

Synchronous job execution blocks the main thread during the Layout and Paint stages, delaying rendering. Asynchronous queuing defers work, allowing the browser to complete rendering faster.

→Layout

→Paint

→Composite

⚠️ BottleneckLayout and Paint stages due to blocking synchronous job execution

Core Web Vital Affected

INP

This affects page load speed and user interaction responsiveness by offloading heavy tasks to background jobs.

Optimization Tips

1Never run slow jobs synchronously during web requests.

2Use perform_later to queue jobs asynchronously.

3Monitor job queue length to avoid delays in background processing.

Performance Quiz - 3 Questions

What is the main performance benefit of queuing jobs asynchronously in Rails?

A It prevents blocking the web request, improving input responsiveness.

B It reduces the number of database queries.

C It decreases the size of the JavaScript bundle.

D It improves CSS selector matching speed.

DevTools: Performance

How to check: Record a performance profile during a web request that triggers job execution. Look for long tasks blocking the main thread.

What to look for: Long blocking tasks in the Main thread timeline indicate synchronous job execution slowing rendering.