performance-optimization

# Performance Optimization — Expert Decisions

Expert decision frameworks for performance choices. Claude knows lazy loading and async basics — this skill provides judgment calls for when to optimize and which tool to use.

---

## Decision Trees

### Should You Optimize?

```
When should you invest in optimization?
├─ User-facing latency issue (visible stutter/delay)
│  └─ YES — Profile and fix
│     Measure first, optimize second
│
├─ Premature concern ("this might be slow")
│  └─ NO — Wait for evidence
│     Write clean code, profile later
│
├─ Battery drain complaints
│  └─ YES — Use Energy Diagnostics
│     Focus on background work, location, network
│
├─ Memory warnings / crashes
│  └─ YES — Use Allocations + Leaks
│     Find retain cycles, unbounded caches
│
└─ App store reviews mention slowness
   └─ YES — Profile real scenarios
      User perception matters
```

**The trap**: Optimizing based on assumptions. Always profile first. The bottleneck is rarely where you think.

### Profiling Tool Selection

```
What are you measuring?
├─ Slow UI / frame drops
│  └─ Time Profiler + View Debugger
│     Find expensive work on main thread
│
├─ Memory growth / leaks
│  └─ Allocations + Leaks instruments
│     Track object lifetimes, find cycles
│
├─ Network performance
│  └─ Network instrument + Charles/Proxyman
│     Latency, payload size, request count
│
├─ Disk I/O issues
│  └─ File Activity instrument
│     Excessive reads/writes
│
├─ Battery drain
│  └─ Energy Log instrument
│     CPU wake, location, networking
│
└─ GPU / rendering
   └─ Core Animation instrument
      Offscreen rendering, overdraw
```

### SwiftUI View Update Strategy

```
View is re-rendering too often?
├─ Caused by parent state changes
│  └─ Extract to separate view
│     Child doesn't depend on changing state
│
├─ Complex computed body
│  └─ Cache expensive computations
│     Use ViewModel or memoization
│
├─ List items all updating
│  └─ Check view identity
│     Use stable IDs, not indices