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이름만 다른(표기 변형) [[위키링크]]를 대상 문서의 canonical 제목으로 치환해 끊겼던 1,200개 링크를 연결. 제목/파일명 정규화 일치만 적용하고 별칭 매칭은 과병합 위험으로 제외(애매성 가드). 원본은 _link_reconcile_backup/ 에 백업. 도구: Datacollect/scripts/link_reconcile_apply.mjs Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
161 lines
5.4 KiB
Markdown
161 lines
5.4 KiB
Markdown
---
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id: wiki-2026-0508-old-space
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title: Old Space (V8)
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category: 10_Wiki/Topics
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status: verified
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canonical_id: self
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aliases: [Old Generation, Tenured Space, V8 Old Space, Major GC heap]
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duplicate_of: none
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source_trust_level: A
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confidence_score: 0.95
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verification_status: applied
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tags: [v8, gc, memory, javascript, runtime]
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raw_sources: []
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last_reinforced: 2026-05-10
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github_commit: pending
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tech_stack:
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language: javascript
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framework: v8
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---
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# Old Space (V8)
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## 매 한 줄
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> **"매 V8 heap의 long-lived object 영역 — Young Gen에서 2번 생존 후 promote, Major GC (Mark-Compact / Mark-Sweep / Concurrent Marking) 대상."**. Generational hypothesis 기반 (Ungar 1984). 2026 현재 V8 13.x · Node 24 · Chrome 130+에서 Orinoco의 concurrent / parallel / incremental marking + Pointer Compression으로 pause time <1ms.
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## 매 핵심
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### 매 V8 heap 구조
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- **New Space (Young Gen)**: 1-8MB, semi-space (Cheney scavenger), allocation 빠름.
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- **Old Space (Old Gen)**: 매 default unbounded (--max-old-space-size 제한), promote target.
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- **Code Space**: JIT compiled code.
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- **Map Space**: Hidden class (V8 maps).
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- **Large Object Space**: ≥ ~256KB single object.
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- **Read-Only Space**: immutable roots.
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### 매 promotion 규칙
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- 매 Young Gen에서 minor GC 2번 survive → Old Space promote.
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- Large object (≥ kMaxRegularHeapObjectSize, ~256KB) → 직접 Old Space (LOS).
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### 매 Major GC (Old Space) 알고리즘
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- **Mark-Compact**: full pause, fragmentation 제거.
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- **Concurrent Marking** (Orinoco): worker thread가 mark, main thread continue.
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- **Incremental Marking**: chunk별 mark, 사이사이 mutator 실행.
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- **Lazy Sweeping**: page별로 sweep on demand.
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### 매 응용
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1. Node.js server — heap profiling으로 leak 추적 (`--inspect`, heapdump).
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2. Chrome — DevTools Memory tab의 retained size 분석.
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3. Performance tuning — `--max-old-space-size=4096`로 limit 조정.
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## 💻 패턴
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### Heap snapshot 생성 (Node.js)
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```javascript
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import { writeHeapSnapshot } from 'node:v8';
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import { performance } from 'node:perf_hooks';
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process.on('SIGUSR2', () => {
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const file = `/tmp/heap-${Date.now()}.heapsnapshot`;
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writeHeapSnapshot(file);
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console.log('snapshot:', file);
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});
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// kill -USR2 <pid>
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```
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### Inspect heap stats
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```javascript
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import v8 from 'node:v8';
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console.log(v8.getHeapSpaceStatistics());
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// [ { space_name: 'old_space', space_size, space_used_size, ... } ]
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console.log(v8.getHeapStatistics());
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// { total_heap_size, used_heap_size, heap_size_limit, ... }
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```
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### Force GC for measurement (--expose-gc)
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```javascript
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// node --expose-gc app.js
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function measureRetained(fn) {
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global.gc(); global.gc();
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const before = process.memoryUsage().heapUsed;
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const ref = fn();
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global.gc(); global.gc();
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const after = process.memoryUsage().heapUsed;
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return { ref, retained: after - before };
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}
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```
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### Trace GC events
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```bash
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node --trace-gc --trace-gc-verbose app.js
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# [12345:0x...] [GC] 100ms: 50.0 (60.0) -> 30.0 (60.0) MB (Mark-Sweep) ...
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```
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### Monitor old space in production (Prometheus)
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```javascript
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import client from 'prom-client';
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import v8 from 'node:v8';
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const oldSpaceUsed = new client.Gauge({
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name: 'nodejs_v8_old_space_used_bytes',
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help: 'V8 old space used',
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});
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setInterval(() => {
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const old = v8.getHeapSpaceStatistics()
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.find(s => s.space_name === 'old_space');
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oldSpaceUsed.set(old.space_used_size);
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}, 5000);
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```
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### Avoid old-space leak — WeakRef / WeakMap for cache
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```javascript
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const cache = new WeakMap(); // key not retained
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function compute(obj) {
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if (cache.has(obj)) return cache.get(obj);
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const v = expensive(obj);
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cache.set(obj, v);
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return v;
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}
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// obj GC'd → cache entry auto-removed
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```
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## 매 결정 기준
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| 상황 | Approach |
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|---|---|
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| Suspected memory leak | heap snapshot diff |
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| OOM under load | `--max-old-space-size=` increase + investigate |
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| Frequent major GC pause | reduce promotion rate (avoid long-lived churn) |
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| Cache growing forever | WeakMap / LRU bound |
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| Need pre-prod heap profile | `--inspect` + DevTools |
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**기본값**: 매 default V8 settings — limit 변경은 측정 후.
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## 🔗 Graph
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- 부모: [[V8 엔진 힙 아키텍처|V8 Heap Architecture]] · [[Garbage_Collection]]
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- 변형: [[Mark-Sweep]] · [[Incremental_Marking]] · [[Generational_Hypothesis]]
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- 응용: [[Orinoco]] · [[Pointer_Compression]] · [[Memory_Leaks]]
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- Adjacent: [[Write Barrier|Write_Barrier]] · [[Snapshots]] · [[Reachability_Analysis]]
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## 🤖 LLM 활용
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**언제**: Node.js memory issue 분석, heap profiling, V8 internals 학습, GC tuning.
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**언제 X**: non-V8 runtime (Bun-JSC, Deno-V8 다르지만 비슷, Hermes는 별도), browser-only DOM leak (different territory).
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## ❌ 안티패턴
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- **Forgotten timer/listener**: 매 closure가 old space에 retain.
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- **Global cache without bound**: 매 monotonic growth → OOM.
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- **Large allocation in hot loop**: Young → Old promotion 폭증, frequent major GC.
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- **String concat in loop without builder**: 매 intermediate retained.
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- **`--max-old-space-size` blindly raised**: 매 leak hide, root cause 회피.
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## 🧪 검증 / 중복
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- Verified (V8 source `v8/src/heap/`, V8 blog Orinoco posts, Node.js v8 module docs 2026).
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- 신뢰도 A.
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- Duplicates: `Old_Space(Old_Generation).md` redirects here.
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## 🕓 Changelog
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| 날짜 | 변경 |
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|---|---|
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| 2026-05-08 | Phase 1 |
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| 2026-05-10 | Manual cleanup — canonical V8 Old Space doc + heap profiling patterns |
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