go-optimization

What this skill does

# Go Optimization Skill

This skill provides expert guidance on Go performance optimization, covering profiling, benchmarking, memory management, and runtime tuning for building high-performance applications.

## When to Use

Activate this skill when:
- Profiling application performance
- Optimizing CPU-intensive operations
- Reducing memory allocations
- Tuning garbage collection
- Writing benchmarks
- Analyzing performance bottlenecks
- Optimizing hot paths
- Reducing lock contention

## Profiling

### CPU Profiling

```go
import (
    "os"
    "runtime/pprof"
)

func main() {
    // Start CPU profiling
    f, err := os.Create("cpu.prof")
    if err != nil {
        log.Fatal(err)
    }
    defer f.Close()

    if err := pprof.StartCPUProfile(f); err != nil {
        log.Fatal(err)
    }
    defer pprof.StopCPUProfile()

    // Your code here
    runApplication()
}

// Analyze:
// go tool pprof cpu.prof
// (pprof) top10
// (pprof) list functionName
// (pprof) web
```

### Memory Profiling

```go
import (
    "os"
    "runtime"
    "runtime/pprof"
)

func writeMemProfile(filename string) {
    f, err := os.Create(filename)
    if err != nil {
        log.Fatal(err)
    }
    defer f.Close()

    runtime.GC() // Force GC before snapshot
    if err := pprof.WriteHeapProfile(f); err != nil {
        log.Fatal(err)
    }
}

// Analyze:
// go tool pprof -alloc_space mem.prof
// go tool pprof -inuse_space mem.prof
```

### HTTP Profiling

```go
import (
    _ "net/http/pprof"
    "net/http"
)

func main() {
    // Enable pprof endpoints
    go func() {
        log.Println(http.ListenAndServe("localhost:6060", nil))
    }()

    // Your application
    runServer()
}

// Access profiles:
// http://localhost:6060/debug/pprof/
// go tool pprof http://localhost:6060/debug/pprof/profile?seconds=30
// go tool pprof http://localhost:6060/debug/pprof/heap
```

### Execution Tracing

```go
import (
    "os"
    "runtime/trace"
)

func main() {
    f, err := os.Create("trace.out")
    if err != nil {
        log.Fatal(err)
    }
    defer f.Close()

    if err := trace.Start(f); err != nil {
        log.Fatal(err)
    }
    defer trace.Stop()

    // Your code
    runApplication()
}

// View trace:
// go tool trace trace.out
```

## Benchmarking

### Basic Benchmarks

```go
func BenchmarkStringConcat(b *testing.B) {
    for i := 0; i < b.N; i++ {
        _ = "hello" + " " + "world"
    }
}

func BenchmarkStringBuilder(b *testing.B) {
    for i := 0; i < b.N; i++ {
        var sb strings.Builder
        sb.WriteString("hello")
        sb.WriteString(" ")
        sb.WriteString("world")
        _ = sb.String()
    }
}

// Run: go test -bench=. -benchmem
```

### Sub-benchmarks

```go
func BenchmarkEncode(b *testing.B) {
    data := generateTestData()

    b.Run("JSON", func(b *testing.B) {
        b.ReportAllocs()
        for i := 0; i < b.N; i++ {
            json.Marshal(data)
        }
    })

    b.Run("MessagePack", func(b *testing.B) {
        b.ReportAllocs()
        for i := 0; i < b.N; i++ {
            msgpack.Marshal(data)
        }
    })
}
```

### Parallel Benchmarks

```go
func BenchmarkConcurrentAccess(b *testing.B) {
    cache := NewCache()

    b.RunParallel(func(pb *testing.PB) {
        for pb.Next() {
            cache.Get("key")
        }
    })
}
```

### Benchmark Comparison

```bash
# Run benchmarks and save results
go test -bench=. -benchmem > old.txt

# Make optimizations

# Run again and compare
go test -bench=. -benchmem > new.txt
benchstat old.txt new.txt
```

## Memory Optimization

### Escape Analysis

```go
// Check what escapes to heap
// go build -gcflags="-m" main.go

// ✅ GOOD: Stack allocation
func stackAlloc() int {
    x := 42
    return x
}

// ❌ BAD: Heap escape
func heapEscape() *int {
    x := 42
    return &x // x escapes to heap
}

// ✅ GOOD: Interface without allocation
func noAlloc(w io.Writer, data []byte) {
    w.Write(data)
}

// ❌ BAD: Interface causes allocation
func withAlloc() io.Writer {
    var b bytes.Buffer
    return &b // &b escapes
}
```

### Pre-allocation

```go
// ❌ BAD: Growing slice
func badAppend(n int) []int {
    var result []int
    for i := 0; i < n; i++ {
        result = append(result, i) // Multiple allocations
    }
    return result
}

// ✅ GOOD: Pre-allocate
func goodAppend(n int) []int {
    result := make([]int, 0, n) // Single allocation
    for i := 0; i < n; i++ {
        result = append(result, i)
    }
    return result
}

// ✅ GOOD: Known length
func knownLength(n int) []int {
    result := make([]int, n)
    for i := 0; i < n; i++ {
        result[i] = i
    }
    return result
}

// ❌ BAD: String concatenation
func badConcat(strs []string) string {
    result := ""
    for _, s := range strs {
        result += s // New allocation each time
    }
    return result
}

// ✅ GOOD: strings.Builder
func goodConcat(strs []string) string {
    var sb strings.Builder
    sb.Grow(estimateSize(strs))
    for _, s := range strs {
        sb.WriteString(s)
    }
    return sb.String()
}
```

### sync.Pool

```go
var bufferPool = sync.Pool{
    New: func() interface{} {
        return new(bytes.Buffer)
    },
}

func processData(data []byte) []byte {
    // Get buffer from pool
    buf := bufferPool.Get().(*bytes.Buffer)
    buf.Reset()
    defer bufferPool.Put(buf)

    // Use buffer
    buf.Write(data)
    // Process...

    return buf.Bytes()
}

// String builder pool
var sbPool = sync.Pool{
    New: func() interface{} {
        return &strings.Builder{}
    },
}

func buildString(parts []string) string {
    sb := sbPool.Get().(*strings.Builder)
    sb.Reset()
    defer sbPool.Put(sb)

    for _, part := range parts {
        sb.WriteString(part)
    }
    return sb.String()
}
```

### Zero-Copy Techniques

```go
// Use byte slices instead of strings
func parseHeader(header []byte) (key, value []byte) {
    i := bytes.IndexByte(header, ':')
    if i < 0 {
        return nil, nil
    }
    return header[:i], header[i+1:]
}

// Reuse buffers
type Parser struct {
    buf []byte
}

func (p *Parser) Parse(data []byte) error {
    p.buf = p.buf[:0] // Reset length, keep capacity
    p.buf = append(p.buf, data...)
    // Process p.buf...
    return nil
}

// Direct writing
func writeResponse(w io.Writer, data interface{}) error {
    enc := json.NewEncoder(w) // Write directly to w
    return enc.Encode(data)
}
```

## Garbage Collection Tuning

### GC Control

```go
import "runtime/debug"

// Adjust GC target percentage
debug.SetGCPercent(100) // Default
// Higher = less frequent GC, more memory
// Lower = more frequent GC, less memory

// Force GC (use sparingly!)
runtime.GC()

// Monitor GC stats
var stats runtime.MemStats
runtime.ReadMemStats(&stats)
fmt.Printf("Alloc = %v MB\n", stats.Alloc/1024/1024)
fmt.Printf("TotalAlloc = %v MB\n", stats.TotalAlloc/1024/1024)
fmt.Printf("Sys = %v MB\n", stats.Sys/1024/1024)
fmt.Printf("NumGC = %v\n", stats.NumGC)
```

### GOGC Environment Variable

```bash
# Default (100%)
GOGC=100 ./myapp

# More aggressive GC (uses less memory)
GOGC=50 ./myapp

# Less frequent GC (uses more memory)
GOGC=200 ./myapp

# Disable GC (for debugging)
GOGC=off ./myapp
```

## Concurrency Optimization

### Reduce Lock Contention

```go
// ❌ BAD: Single lock
type BadCache struct {
    mu    sync.Mutex
    items map[string]interface{}
}

// ✅ GOOD: RWMutex
type GoodCache struct {
    mu    sync.RWMutex
    items map[string]interface{}
}

func (c *GoodCache) Get(key string) interface{} {
    c.mu.RLock()
    defer c.mu.RUnlock()
    return c.items[key]
}

// ✅ BETTER: Sharded locks
type ShardedCache struct {
    shards [256]*shard
}

type shard struct {
    mu    sync.RWMutex
    items map[string]interface{}
}

func (c *ShardedCache) Get(key string) interface{} {
    shard := c.getShard(key)
    shard.mu.RLock()
    defer shard.mu.RUnlock()
    return shard.items[key]
}
```

### Channel Buffering

```go
// ❌ BAD: Unbuffered channel causes blocking
ch := make(chan int)

// ✅ GOO