performance-optimizer

Identifies and fixes performance bottlenecks in code, databases, and APIs. Measures before and after to prove improvements.

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Repository: BEKO2210/Firstbrain
Last source activity: May 17, 2026 at 12:40
Detected SKILL.md language: English
Stars: 15
Forks: 2

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name	performance-optimizer
description	Identifies and fixes performance bottlenecks in code, databases, and APIs. Measures before and after to prove improvements.
type	skill
created	2026-02-27T00:00:00.000Z
domain	ai-ml
category	prompt-engineering
risk	safe
source	community
tags	["skill","ai-ml","prompt-engineering","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 = 'test@example.com';

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..();
 ( user  users) {
  user. =  db..({ : user. }); 
}


 users =  db..()
  .();

-- Check slow query
EXPLAIN SELECT * FROM users WHERE email = 'test@example.com';
-- Shows: Seq Scan (bad)

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

-- Check again
EXPLAIN SELECT * FROM users WHERE email = 'test@example.com';
-- Shows: Index Scan (good)

// 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');

// Bad: Returns all records
const users = await db.users.find();

// Good: Paginated
const users = await db.users.find()
  .limit(20)
  .skip((page - 1) * 20);

// Bad: Hits database every time
app.get('/api/stats', async (req, res) => {
  const stats = await db.stats.calculate(); // Slow
  res.json(stats);
});

// Good: Cache for 5 minutes
const cache = new Map();
app.get('/api/stats', async (req, res) => {
  const cached = cache.get('stats');
  if (cached && Date.now() - cached.time < 300000) {
    return res.json(cached.data);
  }
  
  const stats = await db.stats.calculate();
  cache.set('stats', { data: stats, time: Date.now() });
  res.json(stats);
});

// Bad: Sequential (slow)
const user = await getUser(id);
const posts = await getPosts(id);
const comments = await getComments(id);
// Total: 300ms + 200ms + 150ms = 650ms

// Good: Parallel (fast)
const [user, posts, comments] = await Promise.all([
  getUser(id),
  getPosts(id),
  getComments(id)
]);
// Total: max(300ms, 200ms, 150ms) = 300ms

// Bad: Returns everything
res.json(users); // 5MB response

// Good: Only needed fields
res.json(users.map(u => ({
  id: u.id,
  name: u.name,
  email: u.email
}))); // 500KB response

// Bad: Re-renders on every parent update
function UserList({ users }) {
  return users.map(user => <UserCard user={user} />);
}

// Good: Memoized
const UserCard = React.memo(({ user }) => {
  return <div>{user.name}</div>;
});

// Bad: Imports entire library
import _ from 'lodash'; // 70KB

// Good: Import only what you need
import debounce from 'lodash/debounce'; // 2KB

// Bad: Everything in one bundle
import HeavyComponent from './HeavyComponent';

// Good: Lazy load
const HeavyComponent = React.lazy(() => import('./HeavyComponent'));

<!-- Bad: Large image -->
<img src="photo.jpg" /> <!-- 5MB -->

<!-- Good: Optimized and responsive -->
<img 
  src="photo-small.webp" 
  srcset="photo-small.webp 400w, photo-large.webp 800w"
  loading="lazy"
  width="400"
  height="300"
/> <!-- 50KB -->

// Bad: O(n²) - nested loops
function findDuplicates(arr) {
  const duplicates = [];
  for (let i = 0; i < arr.length; i++) {
    for (let j = i + 1; j < arr.length; j++) {
      if (arr[i] === arr[j]) duplicates.push(arr[i]);
    }
  }
  return duplicates;
}

// Good: O(n) - single pass with Set
function findDuplicates(arr) {
  const seen = new Set();
  const duplicates = new Set();
  for (const item of arr) {
    if (seen.has(item)) duplicates.add(item);
    seen.add(item);
  }
  return Array.from(duplicates);
}

// Bad: Calculates every time
function getTotal(items) {
  return items.reduce((sum, item) => sum + item.price * item.quantity, 0);
}
// Called 100 times in render

// Good: Memoized
const getTotal = useMemo(() => {
  return items.reduce((sum, item) => sum + item.price * item.quantity, 0);
}, [items]);

// Bad: Event listener not cleaned up
useEffect(() => {
  window.addEventListener('scroll', handleScroll);
  // Memory leak!
}, []);

// Good: Cleanup
useEffect(() => {
  window.addEventListener('scroll', handleScroll);
  return () => window.removeEventListener('scroll', handleScroll);
}, []);

// Bad: Loads entire file into memory
const data = fs.readFileSync('huge-file.txt'); // 1GB

// Good: Stream it
const stream = fs.createReadStream('huge-file.txt');
stream.on('data', chunk => process(chunk));

// Before optimization
console.time('query');
const users = await db.users.find();
console.timeEnd('query');
// query: 2341ms

// After optimization (added index)
console.time('query');
const users = await db.users.find();
console.timeEnd('query');
// query: 23ms

// Improvement: 100x faster!

Page Load: < 2 seconds
API Response: < 200ms
Database Query: < 50ms
Bundle Size: < 200KB
Time to Interactive: < 3 seconds