---
id: perf-node-profiling
title: Node Profiling — CPU / Memory / Async hooks
category: Coding
status: draft
source_trust_level: B
verification_status: conceptual
created_at: 2026-05-09
updated_at: 2026-05-09
tags: [performance, node, profiling, vibe-coding]
tech_stack: { language: "Node / TS", applicable_to: ["Backend"] }
applied_in: []
aliases: [clinic, 0x, flamegraph, heapdump, async hooks, --inspect]
---

# Node Profiling

> "느림" 감으로 X — **profile**. **CPU = clinic flame / 0x, Memory = heapdump, Event loop = clinic doctor**. Production = `--inspect` + Chrome DevTools.

## 📖 핵심 개념
- CPU profile: 어느 함수가 시간 소모.
- Heap snapshot: 메모리 누가 보유.
- Event loop lag: 비동기 정체.
- Async hooks: async chain 추적.

## 💻 코드 패턴

### Clinic.js (가장 단순)
```bash
yarn add -D clinic

clinic doctor -- node app.js
# 실행 → 부하 (autocannon) → Ctrl+C
# HTML report: doctor 가 진단 (CPU bound? I/O? memory?)

clinic flame -- node app.js
# Flame graph — 시간 hot spot

clinic bubbleprof -- node app.js
# Async operation 시각화

clinic heapprofiler -- node app.js
# Memory allocation
```

### 0x (flame graph)
```bash
npx 0x app.js
# 또는
0x -- node app.js
```

### --inspect (Chrome DevTools)
```bash
node --inspect app.js
# 또는 prod (조심)
node --inspect=0.0.0.0:9229 app.js

# Chrome → chrome://inspect → DevTools
# CPU profile, heap snapshot, allocation timeline
```

→ Production attach 가능 (보안 주의).

### CPU profile (programmatic)
```ts
import { Session } from 'node:inspector';

const session = new Session();
session.connect();

session.post('Profiler.enable', () => {
  session.post('Profiler.start', () => {
    setTimeout(() => {
      session.post('Profiler.stop', (err, { profile }) => {
        require('fs').writeFileSync('profile.cpuprofile', JSON.stringify(profile));
        // Chrome DevTools → Performance → load profile
      });
    }, 30_000);
  });
});
```

### Heap snapshot
```ts
import { writeHeapSnapshot } from 'node:v8';

// Trigger: signal 또는 API
process.on('SIGUSR2', () => {
  const path = `heap-${Date.now()}.heapsnapshot`;
  writeHeapSnapshot(path);
  console.log('snapshot:', path);
});

// 분석: Chrome DevTools → Memory → Load snapshot
```

```bash
kill -USR2 $PID
```

→ "Comparison" view 로 두 snapshot 비교 → leak.

### Memory leak 패턴
```ts
// ❌ Global Map 만 쌓임
const cache = new Map();
app.get('/x', (req, res) => {
  cache.set(req.id, req.data); // 영원 — leak
});

// ✅ TTL / LRU
import LRU from 'lru-cache';
const cache = new LRU({ max: 1000, ttl: 60_000 });
```

### Event loop lag
```ts
import { monitorEventLoopDelay } from 'node:perf_hooks';

const h = monitorEventLoopDelay({ resolution: 20 });
h.enable();

setInterval(() => {
  console.log('p99 lag:', h.percentile(99) / 1e6, 'ms');
  h.reset();
}, 5000);
```

→ 50ms+ = problem. CPU bound 또는 sync I/O 의심.

### Async hooks (실험적, 비싸)
```ts
import { createHook, executionAsyncId } from 'node:async_hooks';

const stack = new Map();
const hook = createHook({
  init: (asyncId, type, triggerAsyncId) => {
    stack.set(asyncId, { type, parent: triggerAsyncId });
  },
  destroy: (asyncId) => stack.delete(asyncId),
});
hook.enable();
```

→ AsyncLocalStorage 의 internal. Trace 추적.

### AsyncLocalStorage (context)
```ts
import { AsyncLocalStorage } from 'node:async_hooks';

const als = new AsyncLocalStorage<{ requestId: string; userId?: string }>();

app.use((req, res, next) => {
  als.run({ requestId: uuid() }, next);
});

// 어디서나
log.info({ ...als.getStore(), msg: 'event' });
```

### Production tracing (low overhead)
```ts
// OpenTelemetry auto-instrumentation (위 OTel 문서 참조)
// Sentry profiling
import * as Sentry from '@sentry/node';
import { ProfilingIntegration } from '@sentry/profiling-node';

Sentry.init({ dsn, profilesSampleRate: 0.1, integrations: [new ProfilingIntegration()] });
```

→ Continuous profiling — 항상 켜져있음.

### perf_hooks 측정
```ts
import { performance } from 'node:perf_hooks';

const t = performance.now();
await heavyWork();
console.log('took', performance.now() - t, 'ms');

// PerformanceObserver
import { PerformanceObserver, performance } from 'node:perf_hooks';
const obs = new PerformanceObserver((items) => {
  for (const e of items.getEntries()) console.log(e.name, e.duration);
});
obs.observe({ type: 'measure' });

performance.mark('start');
await ...;
performance.mark('end');
performance.measure('myWork', 'start', 'end');
```

### V8 flags (debugging)
```bash
node --max-old-space-size=4096 app.js     # heap 4GB
node --trace-gc app.js                     # GC log
node --prof app.js                         # CPU profile (raw)
node --prof-process isolate-*.log          # process
```

### Memory limit
```bash
# Default V8 = ~1.5 GB on 64-bit
NODE_OPTIONS="--max-old-space-size=4096" node app.js
```

### Hot path 측정 (JIT)
```ts
// 반복 측정 — JIT warmup
for (let i = 0; i < 10000; i++) myHotFn(); // warm
const t = performance.now();
for (let i = 0; i < 100000; i++) myHotFn();
console.log((performance.now() - t) / 100000, 'us per call');
```

## 🤔 의사결정 기준
| 증상 | 도구 |
|---|---|
| CPU 100% | Flame graph (0x / clinic) |
| Memory 자라남 | Heap snapshot diff |
| 응답 느려짐 점진 | Event loop lag |
| 가끔 spike | Continuous profile (Sentry) |
| Async tracing | OTel + auto-instrumentation |
| Production attach | --inspect=0.0.0.0:9229 (보안) |

## ❌ 안티패턴
- **`console.time` 만 + 추측**: 정확 X. profiler.
- **Production --inspect 공개**: 누구나 attach. SSH tunnel.
- **Async hook prod 항상**: 큰 overhead. 디버깅 시만.
- **Heap snapshot prod 큰 process**: GC pause + freeze.
- **JIT warmup 무시**: 첫 call 측정.
- **Memory limit 안 설정 prod**: 무한 자라남.
- **Sample rate 100% prod**: 비용. 1-10%.

## 🤖 LLM 활용 힌트
- Clinic doctor 가 진단 시작.
- Heap snapshot diff 가 leak.
- Event loop lag 가 핵심 SLI.
- Production = Sentry / OTel sampled.

## 🔗 관련 문서
- [[Native_Memory_Profiling]]
- [[DevOps_Observability_Stack]]
- [[Backpressure_Patterns]]
