go-performance-review

Go Performance Review

Profile first, optimize second. Never optimize without a benchmark proving the problem.

1. Allocation Reduction

Prefer strconv over fmt for primitive conversions:

// ✅ Good — zero allocations for simple conversions
s := strconv.Itoa(42)
s := strconv.FormatFloat(3.14, 'f', 2, 64)

// ❌ Bad — fmt.Sprintf allocates
s := fmt.Sprintf("%d", 42)

Avoid unnecessary string-to-byte conversions:

// ✅ Good — use strings.Builder for concatenation
var b strings.Builder
for _, s := range parts {
    b.WriteString(s)
}
result := b.String()

// ❌ Bad — repeated concatenation allocates on every +
result := ""
for _, s := range parts {
    result += s
}

Preallocate slices and maps when size is known:

// ✅ Good — single allocation
users := make([]User, 0, len(ids))
for _, id := range ids {
    users = append(users, getUser(id))
}

// ✅ Good — map with capacity hint
lookup := make(map[string]User, len(users))

// ❌ Bad — repeated growing
var users []User // starts at 0, grows via doubling

Use sync.Pool for frequently allocated, short-lived objects:

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

func process(data []byte) string {
    buf := bufPool.Get().(*bytes.Buffer)
    defer func() {
        buf.Reset()
        bufPool.Put(buf)
    }()

    buf.Write(data)
    return buf.String()
}

2. Hot Path Optimizations

Avoid interface conversions in tight loops:

// ✅ Good — concrete type in loop
func sum(vals []int64) int64 {
    var total int64
    for _, v := range vals {
        total += v
    }
    return total
}

// ❌ Bad — interface{} causes boxing/unboxing
func sum(vals []interface{}) int64 { ... }

Avoid reflect in performance-critical paths:

If you need reflection-like behavior at scale, use code generation (go generate, stringer, protocol buffers).

Reduce pointer chasing:

// ✅ Good — contiguous memory, cache-friendly
type Points struct {
    X []float64
    Y []float64
}

// ❌ Slower — pointer chasing per element
type Points []*Point