# Install clinic.js for Node.js profiling
npm install -g clinic
 
# Generate flame chart
clinic flame -- node server.js
 
# Generate bubbleprof (async bottlenecks)
clinic bubbleprof -- node server.js

// The problematic query
const products = await Product.find({
  category: 'electronics',
  price: { $gte: 100, $lte: 500 },
  inStock: true,
}).sort({ createdAt: -1 }).limit(20)
 
// MongoDB explain() output:
// "stage": "COLLSCAN"  ← Full collection scan! 😱
// "totalDocsExamined": 2,147,483
// "executionTimeMillis": 487

// Added compound index matching the query pattern
db.products.createIndex({
  category: 1,
  inStock: 1,
  price: 1,
  createdAt: -1
})
 
// After indexing:
// "stage": "IXSCAN"  ← Index scan! ✅
// "totalDocsExamined": 847
// "executionTimeMillis": 12

// 1. Index fields you filter on (most selective first)
// ESR Rule: Equality → Sort → Range
 
// ✅ Good: Equality (category) → Sort (createdAt) → Range (price)
{ category: 1, createdAt: -1, price: 1 }
 
// ❌ Bad: Range first → forces scanning more documents
{ price: 1, category: 1, createdAt: -1 }
 
// 2. Cover your queries (include projected fields)
{ category: 1, createdAt: -1, price: 1, name: 1, image: 1 }
// Now MongoDB doesn't even need to read the document — just the index
 
// 3. Monitor slow queries
db.setProfilingLevel(1, { slowms: 100 })
db.system.profile.find().sort({ ts: -1 }).limit(10)

// lib/cache.ts
import Redis from 'ioredis'
 
const redis = new Redis(process.env.REDIS_URL)
 
export async function cacheGet<T>(key: string): Promise<T | null> {
  const data = await redis.get(key)
  return data ? JSON.parse(data) : null
}
 
export async function cacheSet(
  key: string,
  data: any,
  ttlSeconds: number = 300 // 5 minutes default
): Promise<void> {
  await redis.set(key, JSON.stringify(data), 'EX', ttlSeconds)
}
 
export async function cacheInvalidate(pattern: string): Promise<void> {
  const keys = await redis.keys(pattern)
  if (keys.length > 0) {
    await redis.del(...keys)
  }
}
 
// middleware/cache.ts
export function cacheMiddleware(ttl: number = 300) {
  return async (req: Request, res: Response, next: NextFunction) => {
    // Only cache GET requests
    if (req.method !== 'GET') return next()
 
    const key = `api:${req.originalUrl}`
    const cached = await cacheGet(key)
 
    if (cached) {
      res.setHeader('X-Cache', 'HIT')
      return res.json(cached)
    }
 
    // Override res.json to intercept the response and cache it
    const originalJson = res.json.bind(res)
    res.json = (body: any) => {
      cacheSet(key, body, ttl) // Fire and forget
      res.setHeader('X-Cache', 'MISS')
      return originalJson(body)
    }
 
    next()
  }
}
 
// Usage
app.get('/api/products',
  cacheMiddleware(300), // Cache for 5 minutes
  productsController.list
)
 
// Invalidate on writes
app.post('/api/products', async (req, res) => {
  const product = await Product.create(req.body)
  await cacheInvalidate('api:/api/products*') // Clear all product caches
  res.json(product)
})