performance-check

Performance Check Skill

This skill provides a comprehensive performance review checklist for code changes that may impact application performance, scalability, or resource usage.

When to use: When making changes to:

• Database queries and models
• API endpoints (especially list/search operations)
• Frontend rendering logic
• Background jobs and scheduled tasks
• Caching mechanisms
• Large data processing
• File operations
• Network requests
• Recursive algorithms

---

Performance Check Checklist

🗄️ 1. Database Query Optimization

Check for:

• N+1 query problem: Are related records loaded efficiently?
• Missing indexes: Are frequently queried columns indexed?
• **Select ***: Are only needed columns selected?
• Unnecessary joins: Are all joins necessary?
• Query in loop: Are queries executed inside loops?
• Pagination: Are large result sets paginated?
• Eager loading: Are associations preloaded when needed?

Detailed guide: references/database-optimization.md (includes code examples)

---

⚡ 2. API Response Optimization

Check for:

• Response size: Are responses minimized (exclude unnecessary fields)?
• Pagination: Are large lists paginated?
• Filtering: Are list endpoints filterable to reduce data?
• Compression: Is gzip compression enabled?
• Caching headers: Are appropriate cache headers set?
• Partial responses: Can clients request only needed fields?

Detailed guide: references/api-optimization.md (includes load testing example)

---

🎨 3. Frontend Rendering Optimization

Check for:

• Unnecessary re-renders: Are components optimized with React.memo/useMemo/useCallback?
• Large lists: Are large lists virtualized (>100 items)?
• Heavy computations: Are expensive calculations memoized?
• Bundle size: Are large dependencies code-split?
• Image optimization: Are images lazy-loaded and properly sized?
• Debouncing/Throttling: Are frequent events (scroll, input) debounced?

Detailed guide: references/frontend-optimization.md (includes memoization example)

---

💾 4. Caching Strategy

Check for:

• Cache frequently accessed data: Are hot paths cached?
• Cache invalidation: Is stale data properly invalidated?
• Cache TTL: Are appropriate expiration times set?
• Cache key design: Are cache keys unique and predictable?
• Memory limits: Is cache size bounded to prevent memory exhaustion?

Detailed guide: references/caching-strategies.md

---

🔄 5. Concurrency & Parallelization

Check for:

• Blocking operations: Are long operations executed asynchronously?
• Parallel processing: Can independent tasks run concurrently?
• Goroutine leaks: Are goroutines properly cleaned up?
• Race conditions: Are shared resources protected with mutexes?
• Channel buffering: Are channels sized appropriately?

Detailed guide: references/concurrency-guide.md (includes goroutine pool pattern)

---

📦 6. Memory Management

Check for:

• Memory leaks: Are resources (connections, files, goroutines) released?
• Large allocations: Are large objects (slices, maps) pre-allocated when size is known?
• Pointer vs value: Are large structs passed by pointer?
• String concatenation: Is strings.Builder used for building large strings?
• JSON marshaling: Are large objects streamed instead of loaded entirely?

Detailed guide: references/memory-management.md

---

🌐 7. Network & HTTP Optimization

Check for:

• Connection pooling: Are HTTP clients reused (not created per request)?
• Timeouts: Are reasonable timeouts set on all network requests?
• Keep-alive: Are persistent connections used?
• Request batching: Can multiple requests be combined?
• Retry logic: Are failed requests retried with exponential backoff?

Detailed guide: references/network-optimization.md

---

🔍 8. Algorithm Complexity

Check for:

• Time complexity: Is the algorithm O(n²) or worse for large n?
• Space complexity: Does the algorithm use excessive memory?
• Redundant work: Are results computed multiple times?
• Early exit: Can loops exit early when condition is met?

Detailed guide: references/algorithm-complexity.md

---

Performance Testing

Backend Benchmarks

# Run benchmark tests
go test -bench=. -benchmem ./services/

# Profile CPU and memory
go test -cpuprofile=cpu.prof -memprofile=mem.prof -bench=.
go tool pprof cpu.prof

API Load Testing

# Apache Bench
ab -n 1000 -c 10 http://localhost:8000/api/v1/nodes

# k6 (see assets/load-test.js)
k6 run assets/load-test.js

Frontend Performance

Run Lighthouse in Chrome DevTools (F12 → Lighthouse tab):

• First Contentful Paint (FCP): < 1.8s
• Largest Contentful Paint (LCP): < 2.5s
• Time to Interactive (TTI): < 3.8s
• Cumulative Layout Shift (CLS): < 0.1

---

Performance Monitoring

Backend Instrumentation

import "time"

func (s *Service) CriticalOperation() error {
    start := time.Now()
    defer func() {
        log.Infof("Operation duration: %v", time.Since(start))
    }()
    // ... work ...
}

Database Query Monitoring

Enable slow query logging in development:

db, err := gorm.Open(sqlite.Open(dsn), &gorm.Config{
    Logger: logger.New(log.New(os.Stdout, "\r\n", log.LstdFlags), logger.Config{
        SlowThreshold: 200 * time.Millisecond, // Log queries > 200ms
        LogLevel:      logger.Warn,
    }),
})

---

Fallback Strategy

If performance issues are unclear:

1. Use profiler to locate actual bottlenecks (pprof, Chrome DevTools)
2. Measure before optimizing (benchmarks, load tests)
3. Focus on hot paths (90/10 rule - 90% of time in 10% of code)
4. Don't guess - profile and measure

---

Exit Criteria

• All performance issues identified and addressed
• Benchmark tests pass with acceptable performance
• No database queries in loops (or justified and documented)
• Large lists are paginated/virtualized
• Performance implications documented in PR (if significant)
• Monitoring/logging added for new critical paths

---

References

Codebase

• services/mihomo/mihomo.go - Core performance-critical service
• services/scheduler/speedtest_task.go - Concurrent node testing example
• webs/src/views/nodes/ - Frontend list rendering patterns

External

• Go Performance: https://github.com/dgryski/go-perfbook
• React Performance: https://react.dev/learn/render-and-commit
• GORM Performance: https://gorm.io/docs/performance.html