Mailer generation and templates in Ruby on Rails - Performance & Optimization

Performance: Mailer generation and templates

MEDIUM IMPACT

This affects the server response time and initial email generation speed, impacting how fast emails are prepared and sent.

Generating emails with complex templates and inline logic

Ruby on Rails

class UserMailer < ApplicationMailer
  def welcome_email(user)
    @user = user
    mail(to: @user.email, subject: 'Welcome!')
  end
end

# In app/views/user_mailer/welcome_email.html.erb
<h1>Welcome, <%= @user.name %>!</h1>

# In app/views/user_mailer/welcome_email.text.erb
Welcome, <%= @user.name %>!

Precompiled templates avoid inline parsing, reducing CPU load and speeding up email generation.

📈 Performance Gainreduces email generation time by 50-100ms per email, improving throughput

Generating emails with complex templates and inline logic

Ruby on Rails

class UserMailer < ApplicationMailer
  def welcome_email(user)
    @user = user
    mail(to: @user.email, subject: 'Welcome!') do |format|
      format.html { render inline: "<h1>Welcome, <%= @user.name %>!</h1>" }
      format.text { render plain: "Welcome, #{@user.name}!" }
    end
  end
end

Using inline rendering with embedded Ruby in mailer slows down template compilation and increases server CPU usage.

📉 Performance Costblocks email generation for extra 50-100ms per email due to template parsing

Performance Comparison

Pattern	Template Parsing	CPU Load	I/O Blocking	Verdict
Inline ERB in mailer method	High (per email)	High	Low	[X] Bad
Precompiled ERB templates	Low (once)	Low	Low	[OK] Good
Synchronous large file read	Low	Medium	High	[X] Bad
Background job for attachments	Low	Low	Low	[OK] Good

Rendering Pipeline

Mailer templates are compiled and rendered on the server before sending. Inline templates cause extra parsing and CPU usage. Large attachments increase memory and I/O load.

→Template Compilation

→Rendering

→I/O Operations

⚠️ BottleneckTemplate Compilation and File I/O

Optimization Tips

1Avoid inline ERB templates inside mailer methods to reduce CPU parsing overhead.

2Use precompiled templates stored in view files for faster rendering.

3Handle large attachments asynchronously or in background jobs to prevent blocking.

Performance Quiz - 3 Questions

What is a performance downside of using inline ERB templates inside mailer methods?

A It causes template parsing on every email, increasing CPU load.

B It reduces email size significantly.

C It improves caching of templates.

D It speeds up email delivery by avoiding file reads.

DevTools: Rails logs and New Relic (or similar APM)

How to check: Check mailer logs for rendering time and CPU usage; use APM to monitor mailer response times and blocking.

What to look for: Look for long mailer render durations and high CPU spikes during email generation.