performance-optimizer

Performance Optimizer

Find and fix performance bottlenecks. Measure, optimize, verify. Make it fast.

When to Use This Skill

• App is slow or laggy
• User complains about performance
• Page load times are high
• API responses are slow
• Database queries take too long
• User mentions "slow", "lag", "performance", or "optimize"

The Optimization Process

1. Measure First

Never optimize without measuring:

// Measure execution time
console.time('operation');
await slowOperation();
console.timeEnd('operation'); // operation: 2341ms

What to measure:

• Page load time
• API response time
• Database query time
• Function execution time
• Memory usage
• Network requests

2. Find the Bottleneck

Use profiling tools to find the slow parts:

Browser:

DevTools → Performance tab → Record → Stop
Look for long tasks (red bars)

Node.js:

node --prof app.js
node --prof-process isolate-*.log > profile.txt

Database:

EXPLAIN ANALYZE SELECT * FROM users WHERE email = '[email protected]';

3. Optimize

Fix the slowest thing first (biggest impact).

Common Optimizations

Database Queries

Problem: N+1 Queries

// Bad: N+1 queries
const users = await db.users.find();
for (const user of users) {
  user.posts = await db.posts.find({ userId: user.id }); // N queries
}

// Good: Single query with JOIN
const users = await db.users.find()
  .populate('posts'); // 1 query

Problem: Missing Index

-- Check slow query
EXPLAIN SELECT * FROM users WHERE email = '[email protected]';
-- Shows: Seq Scan (bad)

-- Add index
CREATE INDEX idx_users_email ON users(email);

-- Check again
EXPLAIN SELECT * FROM users WHERE email = '[email protected]';
-- Shows: Index Scan (good)

**Problem: SELECT ***

// Bad: Fetches all columns
const users = await db.query('SELECT * FROM users');

// Good: Only needed columns
const users = await db.query('SELECT id, name, email FROM users');