// CPU profiling
const profiler = require('v8-profiler-next');
profiler.startProfiling('CPU profile');
// ... code to profile
const profile = profiler.stopProfiling();
profile.export((error, result) => {
  fs.writeFileSync('profile.cpuprofile', result);
});

import cProfile
import pstats

profiler = cProfile.Profile()
profiler.enable()

# Code to profile
expensive_function()

profiler.disable()
stats = pstats.Stats(profiler)
stats.sort_stats('cumulative')
stats.print_stats(20)

-- PostgreSQL
EXPLAIN ANALYZE
SELECT u.name, COUNT(o.id) as order_count
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE u.created_at > '2024-01-01'
GROUP BY u.id;

-- Add index
CREATE INDEX idx_orders_user_id ON orders(user_id);
CREATE INDEX idx_users_created_at ON users(created_at);

// ❌ Bad - N+1 queries
const users = await User.findAll();
for (const user of users) {
  user.orders = await Order.findAll({ where: { userId: user.id } });
}

// ✅ Good - Single query with eager loading
const users = await User.findAll({
  include: [{ model: Order }]
});

// React lazy loading
const Dashboard = lazy(() => import('./Dashboard'));

function App() {
  return (
    <Suspense fallback={<Loading />}>
      <Dashboard />
    </Suspense>
  );
}

<!-- Responsive images -->
<picture>
  <source srcset="image.webp" type="image/webp">
  <source srcset="image.jpg" type="image/jpeg">
  <img src="image.jpg" alt="Description" loading="lazy">
</picture>

// Redis caching
async function getUser(id: string) {
  const cacheKey = `user:${id}`;
  
  // Check cache
  const cached = await redis.get(cacheKey);
  if (cached) return JSON.parse(cached);
  
  // Fetch from DB
  const user = await db.users.findById(id);
  
  // Store in cache (5 min TTL)
  await redis.setex(cacheKey, 300, JSON.stringify(user));
  
  return user;
}

// Web Vitals
import { getCLS, getFID, getFCP, getLCP, getTTFB } from 'web-vitals';

getCLS(console.log);  // Cumulative Layout Shift
getFID(console.log);  // First Input Delay
getFCP(console.log);  // First Contentful Paint
getLCP(console.log);  // Largest Contentful Paint
getTTFB(console.log); // Time to First Byte