Login and logout flow in Ruby on Rails - Performance & Optimization

Performance: Login and logout flow

MEDIUM IMPACT

This affects page load speed and interaction responsiveness during user authentication.

Handling user login with page reloads

Ruby on Rails

def create
  user = User.find_by(email: params[:email])
  if user&.authenticate(params[:password])
    session[:user_id] = user.id
    respond_to do |format|
      format.turbo_stream { render turbo_stream: turbo_stream.replace('login_form', partial: 'logged_in') }
      format.html { redirect_to root_path }
    end
  else
    flash.now[:alert] = 'Invalid credentials'
    render :new
  end
end

Using Turbo Streams updates only part of the page without full reload, improving responsiveness.

📈 Performance GainNon-blocking partial update reduces interaction delay by 50-70%

Handling user login with page reloads

Ruby on Rails

def create
  user = User.find_by(email: params[:email])
  if user&.authenticate(params[:password])
    session[:user_id] = user.id
    redirect_to root_path
  else
    flash.now[:alert] = 'Invalid credentials'
    render :new
  end
end

Redirect causes full page reload, blocking rendering and delaying interaction readiness.

📉 Performance CostBlocks rendering for 200-500ms depending on network and server response

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Full page reload on login/logout	High (full DOM rebuild)	1+ (full layout)	High (full repaint)	[X] Bad
Partial DOM update with Turbo Streams	Low (targeted DOM changes)	0-1 (localized layout)	Low (partial repaint)	[OK] Good

Rendering Pipeline

Login/logout flows affect the browser's rendering pipeline by triggering network requests, DOM updates, and layout recalculations depending on how the page updates after authentication.

→Network

→Style Calculation

→Layout

→Paint

→Composite

⚠️ BottleneckLayout and Paint stages due to full page reloads and DOM replacements

Core Web Vital Affected

INP

This affects page load speed and interaction responsiveness during user authentication.

Optimization Tips

1Avoid full page reloads on login/logout to reduce blocking rendering.

2Use partial DOM updates (e.g., Turbo Streams) to improve interaction responsiveness.

3Minimize layout shifts by updating only necessary page parts during authentication.

Performance Quiz - 3 Questions

What is the main performance drawback of using full page reloads for login/logout?

A It blocks rendering and causes layout shifts.

B It reduces server load.

C It improves caching efficiency.

D It decreases network requests.

DevTools: Performance

How to check: Record a login or logout action, then analyze the flame chart for long tasks and layout shifts.

What to look for: Look for long blocking times during navigation and large layout or paint events indicating full page reloads.