2nd/10_Wiki/Topics/AI_and_ML/Debugging Methods.md

---
id: wiki-2026-0508-debugging-methods
title: Debugging Methods
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [debugging, frontend debugging, observability, Sentry, LogRocket, time-travel debug, session replay]
duplicate_of: none
source_trust_level: A
confidence_score: 0.93
verification_status: applied
tags: [debugging, observability, sentry, logrocket, devtools, error-boundary, time-travel, profiling]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: JS / Python / Go
  framework: Sentry / Datadog / Chrome DevTools / Redux DevTools
---

# Debugging Methods

## 매 한 줄
> **"매 hypothesis-driven 의 systematic"**. 매 reproduce → 매 narrow → 매 hypothesize → 매 test → 매 fix → 매 prevent. 매 modern: 매 observability (Sentry, Datadog) + 매 session replay + 매 distributed trace + 매 LLM-aided.

## 매 핵심 process

### Scientific debugging
1. **Reproduce**: 매 minimum reproducer.
2. **Observe**: 매 relevant signal.
3. **Hypothesize**: 매 specific cause.
4. **Test**: 매 verify hypothesis.
5. **Fix**: 매 root cause.
6. **Prevent**: 매 test + 매 doc + 매 monitor.

### 매 method

#### Print / Log debugging
- 매 simplest.
- 매 strategic placement.

#### Debugger (breakpoint)
- 매 step-through.
- 매 inspect state.
- 매 conditional breakpoint.

#### Logging + observability
- 매 structured log.
- 매 distributed trace.
- 매 metric.

#### Time-travel
- 매 Redux DevTools, Reduxify.
- 매 action replay.

#### Differential
- 매 git bisect.
- 매 binary search of commits.

#### Rubber duck
- 매 explain to inanimate.
- 매 self-clarification.

#### Profiling
- 매 CPU / memory / GPU.

### 매 modern stack

#### Frontend
- **Sentry**: error tracking + session replay.
- **LogRocket**: session replay focus.
- **Datadog RUM**.
- **PostHog**.
- **Chrome DevTools** (Performance + Memory).
- **React DevTools**.
- **Redux DevTools**.

#### Backend
- **Sentry**: error tracking.
- **Datadog APM** / **New Relic**.
- **OpenTelemetry**: standard.
- **Honeycomb**: 매 observability 의 best.
- **Jaeger / Zipkin**: tracing.

#### Logs / metrics
- **Grafana + Loki + Prometheus**.
- **ELK / OpenSearch**.

### LLM-aided debugging
- **Cursor / Copilot**: 매 inline suggestion.
- **Cody / Continue**: 매 codebase-aware.
- **Sentry AI**: 매 root cause suggest.
- **Stack trace → 매 LLM 의 fix proposal**.

### 매 prevention
- **Type check** (TypeScript).
- **Linter** (ESLint).
- **Test** (unit / integration / e2e).
- **Property-based test**.
- **Sanitizer** (UBSan, ASan, TSan).
- **Fuzz test**.

## 💻 패턴

### Sentry (frontend)
```ts
import * as Sentry from '@sentry/react';

Sentry.init({
  dsn: process.env.SENTRY_DSN,
  integrations: [
    Sentry.browserTracingIntegration(),
    Sentry.replayIntegration({
      maskAllText: true,  // 매 PII protection
      blockAllMedia: true,
    }),
  ],
  tracesSampleRate: 0.1,  // 매 10%
  replaysSessionSampleRate: 0.05,
  replaysOnErrorSampleRate: 1.0,  // 매 100% on error
  release: process.env.RELEASE,
  environment: process.env.NODE_ENV,
});

// 매 manual breadcrumb
Sentry.addBreadcrumb({
  category: 'auth',
  message: 'User logged in',
  level: 'info',
});

// 매 manual capture
try {
  riskyOperation();
} catch (e) {
  Sentry.captureException(e, {
    tags: { feature: 'checkout' },
    extra: { orderId: '...' },
  });
}
```

### Error Boundary (React)
```tsx
class ErrorBoundary extends React.Component {
  state = { hasError: false };
  
  static getDerivedStateFromError() {
    return { hasError: true };
  }
  
  componentDidCatch(error, info) {
    Sentry.captureException(error, { extra: info });
  }
  
  render() {
    if (this.state.hasError) return <Fallback />;
    return this.props.children;
  }
}

<ErrorBoundary>
  <App />
</ErrorBoundary>
```

### Distributed tracing (OpenTelemetry)
```python
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchSpanProcessor
from opentelemetry.exporter.otlp.proto.grpc.trace_exporter import OTLPSpanExporter

provider = TracerProvider()
provider.add_span_processor(BatchSpanProcessor(OTLPSpanExporter()))
trace.set_tracer_provider(provider)

tracer = trace.get_tracer(__name__)

@tracer.start_as_current_span('handle_request')
def handle(req):
    span = trace.get_current_span()
    span.set_attribute('user.id', req.user.id)
    
    with tracer.start_as_current_span('db_query') as db_span:
        db_span.set_attribute('db.statement', 'SELECT * FROM users WHERE id = ?')
        result = db.query(...)
    
    return result
```

### git bisect (commit-level)
```bash
git bisect start
git bisect bad HEAD            # 매 broken now
git bisect good v1.0           # 매 known good

# 매 매 step:
# Run test → 'good' or 'bad'
git bisect good

# 매 끝나면
git bisect reset
```

### Time-travel (Redux DevTools)
```ts
import { configureStore } from '@reduxjs/toolkit';

const store = configureStore({
  reducer: rootReducer,
  devTools: process.env.NODE_ENV !== 'production',
});

// 매 매 action 의 record + 매 replay 가능.
```

### Memory leak detection
```js
// 매 [[Chrome DevTools 메모리 프로파일링]] 참조

// 매 3-snapshot technique
// 1. Heap snapshot baseline.
// 2. 매 suspect action × 5.
// 3. Heap snapshot.
// 4. Compare → detached DOM, growing objects.
```

### Performance profiling
```js
// 매 Chrome DevTools Performance tab
performance.mark('start_search');
const results = expensiveSearch(query);
performance.mark('end_search');
performance.measure('search', 'start_search', 'end_search');

// 매 prod: web-vitals + measurement
import { onINP } from 'web-vitals';
onINP(metric => sendToAnalytics(metric));
```

### Reproducible bug report
```markdown
## Repro
1. ...
2. ...

## Expected
...

## Actual
...

## Environment
- Browser: Chrome 130
- OS: macOS 15
- Build: abc123 (commit: SHA)
- User: id 42 (test account)

## Logs / screenshots
[Sentry link, console output, screenshot]
```

### Property-based test (Hypothesis / fast-check)
```python
from hypothesis import given, strategies as st

@given(st.integers(), st.integers())
def test_addition_commutative(a, b):
    assert add(a, b) == add(b, a)
```

### LLM-aided debug (stack trace)
```python
def llm_suggest_fix(error_message, traceback, code_context):
    prompt = f"""Bug report:
Error: {error_message}

Traceback:
{traceback}

Code context:
{code_context}

Suggest:
1. Most likely root cause (1-2 sentences).
2. Specific fix (code diff).
3. How to prevent recurrence (test, type, validation).

Be specific, no generic advice."""
    return llm.generate(prompt)
```

### Bisection (manual binary search)
```python
def bisect_failing_input(test_fn, inputs):
    """매 매 input 의 specific 의 fail 하는 case 의 narrow."""
    lo, hi = 0, len(inputs) - 1
    while lo < hi:
        mid = (lo + hi) // 2
        if test_fn(inputs[:mid + 1]).failed:
            hi = mid
        else:
            lo = mid + 1
    return inputs[lo]
```

### Conditional breakpoint
```js
// 매 Chrome DevTools: 매 매 breakpoint 의 right-click → "Edit breakpoint" → condition
// 매 example: user.id === 42 && retryCount > 5
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Reproducible | Debugger + breakpoint |
| Production | Sentry + session replay |
| Performance | DevTools Performance + APM |
| Memory leak | Heap snapshot 3-shot |
| Distributed | OpenTelemetry trace |
| Bisection | git bisect |
| Cannot reproduce | Session replay + log search |
| Heisenbug | Differential debug + logging |

**기본값**: Sentry + DevTools + git bisect + LLM assist.

## 🔗 Graph
- 부모: [[Debugging]] · [[Observability]]
- 변형: [[Sentry]] · [[OpenTelemetry]] · [[LogRocket]]
- 응용: [[Chrome DevTools 메모리 프로파일링]] · [[Bottlenecks]] · [[CI_CD 파이프라인 및 IDE 통합 보안]]
- Adjacent: [[Concept-Drift]] · [[Quality_Code_Review_Modern]] · [[Bottlenecks]] · [[Code_Smells]]

## 🤖 LLM 활용
**언제**: 매 stack trace analysis. 매 root cause hypothesis. 매 test design.
**언제 X**: 매 sensitive data (no upload to LLM).

## ❌ 안티패턴
- **No reproducer**: 매 hard to fix.
- **No observability**: 매 prod 의 silent.
- **Print all the things** (no structure): 매 noise.
- **No sample / batch**: 매 cost ↑.
- **Skip prevention** (no test for fix): 매 regression.
- **Privacy 의 ignore** (session replay): 매 PII leak.

## 🧪 검증 / 중복
- Verified (Sentry / Datadog docs, OpenTelemetry standard, Chrome DevTools).
- 신뢰도 A.
- Related: [[Chrome DevTools 메모리 프로파일링]] · [[Bottlenecks]] · [[CI_CD 파이프라인 및 IDE 통합 보안]] · [[Quality_Code_Review_Modern]] · [[Concept-Drift]].

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — process + tools + 매 Sentry / OTel / git bisect / LLM debug code |