Struct layout article

main.go

package main

import (
	"unsafe"
)

// Poor layout - fields ordered by size
type PoorLayout struct {
	a bool  // 1 byte
	b int64 // 8 bytes
	c bool  // 1 byte
	d int32 // 4 bytes
	e bool  // 1 byte
}

// Optimized layout - larger fields first
type OptimizedLayout struct {
	b int64 // 8 bytes
	d int32 // 4 bytes
	a bool  // 1 byte
	c bool  // 1 byte
	e bool  // 1 byte
}

func main() {
	// Print struct sizes
	println("PoorLayout size:", unsafe.Sizeof(PoorLayout{}), "bytes")
	println("OptimizedLayout size:", unsafe.Sizeof(OptimizedLayout{}), "bytes")
}

main_test.go

package main

import "testing"

// Benchmark to measure memory allocation
func BenchmarkMemoryAllocation(b *testing.B) {
	b.Run("PoorLayout", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			_ = make([]PoorLayout, 1000000)
		}
	})

	b.Run("OptimizedLayout", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			_ = make([]OptimizedLayout, 1000000)
		}
	})
}

// Benchmark to measure access time
func BenchmarkFieldAccess(b *testing.B) {
	poor := make([]PoorLayout, 1000000)
	optimized := make([]OptimizedLayout, 1000000)

	b.Run("PoorLayout", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			for j := range poor {
				poor[j].b = int64(j)
			}
		}
	})

	b.Run("OptimizedLayout", func(b *testing.B) {
		for i := 0; i < b.N; i++ {
			for j := range optimized {
				optimized[j].b = int64(j)
			}
		}
	})
}

To get outputs:

go test -bench=. -benchmem