performance-optimizer

Performance Optimizer

When to use this skill

• Application or endpoint is slow
• Database queries taking too long
• High memory usage or memory leaks
• Frontend load times need improvement
• Need to handle higher throughput
• Optimizing build or CI/CD times

Step 1: Measure first

Never optimize without measuring. Identify the actual bottleneck.

Backend profiling

# Node.js — CPU profile
node --prof app.js
node --prof-process isolate-*.log > processed.txt

# Node.js — built-in profiler
node --inspect app.js  # Then open chrome://inspect

# Python — cProfile
python -m cProfile -s cumtime app.py
python -m cProfile -o output.prof app.py  # Save for analysis

# HTTP endpoint timing
curl -w "@curl-format.txt" -o /dev/null -s http://localhost:3000/api/users
# curl-format.txt contains: time_total, time_connect, time_starttransfer

Database profiling

-- PostgreSQL: Identify slow queries
SELECT query, mean_exec_time, calls, total_exec_time
FROM pg_stat_statements
ORDER BY mean_exec_time DESC
LIMIT 20;

-- Explain a slow query
EXPLAIN ANALYZE SELECT * FROM orders
WHERE user_id = 123 AND status = 'active'
ORDER BY created_at DESC;

Frontend profiling

# Lighthouse CLI
npx lighthouse http://localhost:3000 --output=json --output-path=./report.json

# Bundle size analysis
npx webpack-bundle-analyzer stats.json
npx vite-bundle-visualizer

Step 2: Common bottlenecks and fixes

N+1 queries

// BAD: N+1 — one query per user
const users = await db.query('SELECT * FROM users');
for (const user of users) {
  user.orders = await db.query('SELECT * FROM orders WHERE user_id = $1', [user.id]);
}

// GOOD: 2 queries total
const users = await db.query('SELECT * FROM users');
const userIds = users.map(u => u.id);
const orders = await db.query('SELECT * FROM orders WHERE user_id = ANY($1)', [userIds]);
const ordersByUser = groupBy(orders, 'user_id');
users.forEach(u => u.orders = ordersByUser[u.id] ?? []);