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144 lines
3.0 KiB
Markdown
144 lines
3.0 KiB
Markdown
---
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name: performance-profiling
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description: Performance profiling principles. Measurement, analysis, and optimization techniques.
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allowed-tools: Read, Glob, Grep, Bash
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---
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# Performance Profiling
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> Measure, analyze, optimize - in that order.
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## 🔧 Runtime Scripts
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**Execute these for automated profiling:**
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| Script | Purpose | Usage |
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|--------|---------|-------|
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| `scripts/lighthouse_audit.py` | Lighthouse performance audit | `python scripts/lighthouse_audit.py https://example.com` |
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---
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## 1. Core Web Vitals
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### Targets
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| Metric | Good | Poor | Measures |
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|--------|------|------|----------|
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| **LCP** | < 2.5s | > 4.0s | Loading |
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| **INP** | < 200ms | > 500ms | Interactivity |
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| **CLS** | < 0.1 | > 0.25 | Stability |
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### When to Measure
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| Stage | Tool |
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|-------|------|
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| Development | Local Lighthouse |
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| CI/CD | Lighthouse CI |
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| Production | RUM (Real User Monitoring) |
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---
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## 2. Profiling Workflow
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### The 4-Step Process
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```
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1. BASELINE → Measure current state
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2. IDENTIFY → Find the bottleneck
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3. FIX → Make targeted change
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4. VALIDATE → Confirm improvement
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```
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### Profiling Tool Selection
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| Problem | Tool |
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|---------|------|
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| Page load | Lighthouse |
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| Bundle size | Bundle analyzer |
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| Runtime | DevTools Performance |
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| Memory | DevTools Memory |
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| Network | DevTools Network |
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---
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## 3. Bundle Analysis
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### What to Look For
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| Issue | Indicator |
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|-------|-----------|
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| Large dependencies | Top of bundle |
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| Duplicate code | Multiple chunks |
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| Unused code | Low coverage |
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| Missing splits | Single large chunk |
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### Optimization Actions
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| Finding | Action |
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|---------|--------|
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| Big library | Import specific modules |
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| Duplicate deps | Dedupe, update versions |
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| Route in main | Code split |
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| Unused exports | Tree shake |
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---
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## 4. Runtime Profiling
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### Performance Tab Analysis
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| Pattern | Meaning |
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|---------|---------|
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| Long tasks (>50ms) | UI blocking |
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| Many small tasks | Possible batching opportunity |
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| Layout/paint | Rendering bottleneck |
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| Script | JavaScript execution |
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### Memory Tab Analysis
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| Pattern | Meaning |
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|---------|---------|
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| Growing heap | Possible leak |
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| Large retained | Check references |
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| Detached DOM | Not cleaned up |
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---
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## 5. Common Bottlenecks
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### By Symptom
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| Symptom | Likely Cause |
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|---------|--------------|
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| Slow initial load | Large JS, render blocking |
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| Slow interactions | Heavy event handlers |
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| Jank during scroll | Layout thrashing |
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| Growing memory | Leaks, retained refs |
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---
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## 6. Quick Win Priorities
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| Priority | Action | Impact |
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|----------|--------|--------|
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| 1 | Enable compression | High |
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| 2 | Lazy load images | High |
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| 3 | Code split routes | High |
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| 4 | Cache static assets | Medium |
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| 5 | Optimize images | Medium |
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---
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## 7. Anti-Patterns
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| ❌ Don't | ✅ Do |
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|----------|-------|
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| Guess at problems | Profile first |
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| Micro-optimize | Fix biggest issue |
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| Optimize early | Optimize when needed |
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| Ignore real users | Use RUM data |
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---
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> **Remember:** The fastest code is code that doesn't run. Remove before optimizing.
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