[G1-Sync] Manual knowledge update
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Antigravity Agent
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id: perf-node-profiling
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title: Node Profiling — CPU / Memory / Async hooks
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category: Coding
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status: draft
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source_trust_level: B
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verification_status: conceptual
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created_at: 2026-05-09
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updated_at: 2026-05-09
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tags: [performance, node, profiling, vibe-coding]
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tech_stack: { language: "Node / TS", applicable_to: ["Backend"] }
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applied_in: []
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aliases: [clinic, 0x, flamegraph, heapdump, async hooks, --inspect]
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---
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# Node Profiling
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> "느림" 감으로 X — **profile**. **CPU = clinic flame / 0x, Memory = heapdump, Event loop = clinic doctor**. Production = `--inspect` + Chrome DevTools.
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## 📖 핵심 개념
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- CPU profile: 어느 함수가 시간 소모.
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- Heap snapshot: 메모리 누가 보유.
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- Event loop lag: 비동기 정체.
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- Async hooks: async chain 추적.
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## 💻 코드 패턴
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### Clinic.js (가장 단순)
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```bash
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yarn add -D clinic
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clinic doctor -- node app.js
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# 실행 → 부하 (autocannon) → Ctrl+C
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# HTML report: doctor 가 진단 (CPU bound? I/O? memory?)
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clinic flame -- node app.js
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# Flame graph — 시간 hot spot
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clinic bubbleprof -- node app.js
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# Async operation 시각화
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clinic heapprofiler -- node app.js
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# Memory allocation
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```
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### 0x (flame graph)
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```bash
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npx 0x app.js
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# 또는
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0x -- node app.js
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```
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### --inspect (Chrome DevTools)
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```bash
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node --inspect app.js
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# 또는 prod (조심)
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node --inspect=0.0.0.0:9229 app.js
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# Chrome → chrome://inspect → DevTools
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# CPU profile, heap snapshot, allocation timeline
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```
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→ Production attach 가능 (보안 주의).
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### CPU profile (programmatic)
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```ts
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import { Session } from 'node:inspector';
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const session = new Session();
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session.connect();
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session.post('Profiler.enable', () => {
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session.post('Profiler.start', () => {
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setTimeout(() => {
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session.post('Profiler.stop', (err, { profile }) => {
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require('fs').writeFileSync('profile.cpuprofile', JSON.stringify(profile));
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// Chrome DevTools → Performance → load profile
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});
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}, 30_000);
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});
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});
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```
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### Heap snapshot
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```ts
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import { writeHeapSnapshot } from 'node:v8';
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// Trigger: signal 또는 API
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process.on('SIGUSR2', () => {
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const path = `heap-${Date.now()}.heapsnapshot`;
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writeHeapSnapshot(path);
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console.log('snapshot:', path);
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});
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// 분석: Chrome DevTools → Memory → Load snapshot
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```
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```bash
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kill -USR2 $PID
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```
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→ "Comparison" view 로 두 snapshot 비교 → leak.
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### Memory leak 패턴
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```ts
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// ❌ Global Map 만 쌓임
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const cache = new Map();
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app.get('/x', (req, res) => {
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cache.set(req.id, req.data); // 영원 — leak
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});
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// ✅ TTL / LRU
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import LRU from 'lru-cache';
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const cache = new LRU({ max: 1000, ttl: 60_000 });
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```
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### Event loop lag
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```ts
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import { monitorEventLoopDelay } from 'node:perf_hooks';
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const h = monitorEventLoopDelay({ resolution: 20 });
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h.enable();
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setInterval(() => {
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console.log('p99 lag:', h.percentile(99) / 1e6, 'ms');
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h.reset();
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}, 5000);
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```
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→ 50ms+ = problem. CPU bound 또는 sync I/O 의심.
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### Async hooks (실험적, 비싸)
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```ts
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import { createHook, executionAsyncId } from 'node:async_hooks';
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const stack = new Map();
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const hook = createHook({
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init: (asyncId, type, triggerAsyncId) => {
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stack.set(asyncId, { type, parent: triggerAsyncId });
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},
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destroy: (asyncId) => stack.delete(asyncId),
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});
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hook.enable();
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```
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→ AsyncLocalStorage 의 internal. Trace 추적.
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### AsyncLocalStorage (context)
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```ts
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import { AsyncLocalStorage } from 'node:async_hooks';
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const als = new AsyncLocalStorage<{ requestId: string; userId?: string }>();
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app.use((req, res, next) => {
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als.run({ requestId: uuid() }, next);
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});
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// 어디서나
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log.info({ ...als.getStore(), msg: 'event' });
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```
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### Production tracing (low overhead)
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```ts
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// OpenTelemetry auto-instrumentation (위 OTel 문서 참조)
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// Sentry profiling
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import * as Sentry from '@sentry/node';
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import { ProfilingIntegration } from '@sentry/profiling-node';
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Sentry.init({ dsn, profilesSampleRate: 0.1, integrations: [new ProfilingIntegration()] });
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```
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→ Continuous profiling — 항상 켜져있음.
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### perf_hooks 측정
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```ts
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import { performance } from 'node:perf_hooks';
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const t = performance.now();
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await heavyWork();
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console.log('took', performance.now() - t, 'ms');
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// PerformanceObserver
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import { PerformanceObserver, performance } from 'node:perf_hooks';
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const obs = new PerformanceObserver((items) => {
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for (const e of items.getEntries()) console.log(e.name, e.duration);
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});
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obs.observe({ type: 'measure' });
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performance.mark('start');
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await ...;
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performance.mark('end');
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performance.measure('myWork', 'start', 'end');
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```
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### V8 flags (debugging)
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```bash
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node --max-old-space-size=4096 app.js # heap 4GB
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node --trace-gc app.js # GC log
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node --prof app.js # CPU profile (raw)
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node --prof-process isolate-*.log # process
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```
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### Memory limit
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```bash
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# Default V8 = ~1.5 GB on 64-bit
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NODE_OPTIONS="--max-old-space-size=4096" node app.js
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```
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### Hot path 측정 (JIT)
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```ts
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// 반복 측정 — JIT warmup
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for (let i = 0; i < 10000; i++) myHotFn(); // warm
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const t = performance.now();
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for (let i = 0; i < 100000; i++) myHotFn();
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console.log((performance.now() - t) / 100000, 'us per call');
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```
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## 🤔 의사결정 기준
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| 증상 | 도구 |
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| CPU 100% | Flame graph (0x / clinic) |
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| Memory 자라남 | Heap snapshot diff |
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| 응답 느려짐 점진 | Event loop lag |
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| 가끔 spike | Continuous profile (Sentry) |
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| Async tracing | OTel + auto-instrumentation |
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| Production attach | --inspect=0.0.0.0:9229 (보안) |
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## ❌ 안티패턴
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- **`console.time` 만 + 추측**: 정확 X. profiler.
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- **Production --inspect 공개**: 누구나 attach. SSH tunnel.
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- **Async hook prod 항상**: 큰 overhead. 디버깅 시만.
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- **Heap snapshot prod 큰 process**: GC pause + freeze.
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- **JIT warmup 무시**: 첫 call 측정.
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- **Memory limit 안 설정 prod**: 무한 자라남.
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- **Sample rate 100% prod**: 비용. 1-10%.
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## 🤖 LLM 활용 힌트
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- Clinic doctor 가 진단 시작.
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- Heap snapshot diff 가 leak.
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- Event loop lag 가 핵심 SLI.
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- Production = Sentry / OTel sampled.
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## 🔗 관련 문서
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- [[Native_Memory_Profiling]]
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- [[DevOps_Observability_Stack]]
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- [[Backpressure_Patterns]]
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