bytes.Buffer vs make

main_test.go

package app

import (
	"bytes"
	"testing"
)

const ALLOC_SIZE = 64 * 1024 * 1024

func BenchmarkAlloc1(b *testing.B) {
	for i := 0; i < b.N; i++ {
		v := make([]byte, 0, ALLOC_SIZE)
		if len(v) != 0 {
			b.Fatal("oops")
		}
	}
}

func BenchmarkAlloc2(b *testing.B) {
	for i := 0; i < b.N; i++ {
		v := new(bytes.Buffer)
		if len(v.Bytes()) != 0 {
			b.Fatal("oops")
		}
	}
}

func BenchmarkAlloc3(b *testing.B) {
	for i := 0; i < b.N; i++ {
		v := new(bytes.Buffer)
		v.Grow(ALLOC_SIZE)
		if len(v.Bytes()) != 0 {
			b.Fatal("oops")
		}
	}
}

func BenchmarkWrite1(b *testing.B) {
	for i := 0; i < b.N; i++ {
		v := make([]byte, 0, ALLOC_SIZE)
		fill(v, '1', 0, ALLOC_SIZE)
	}
}

func BenchmarkWrite2(b *testing.B) {
	for i := 0; i < b.N; i++ {
		v := new(bytes.Buffer)
		fill(v.Bytes(), '2', 0, ALLOC_SIZE)
	}
}

func BenchmarkWrite3(b *testing.B) {
	for i := 0; i < b.N; i++ {
		v := new(bytes.Buffer)
		v.Grow(ALLOC_SIZE)
		fill(v.Bytes(), '3', 0, ALLOC_SIZE)
	}
}

func fill(slice []byte, val byte, start, end int) {
	for i := start; i < end; i++ {
		slice = append(slice, val)
	}
}

Result

at 13:56:36 ❯ go test -bench . -benchmem
goos: darwin
goarch: amd64
pkg: app
cpu: Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
BenchmarkAlloc1-8            337           2976935 ns/op        67108871 B/op          1 allocs/op
BenchmarkAlloc2-8       1000000000               0.3202 ns/op          0 B/op          0 allocs/op
BenchmarkAlloc3-8            375           2950193 ns/op        67108873 B/op          1 allocs/op
BenchmarkWrite1-8             16          66047937 ns/op        67108876 B/op          1 allocs/op
BenchmarkWrite2-8             12          85604838 ns/op        338720834 B/op        54 allocs/op
BenchmarkWrite3-8             26          44761869 ns/op        67108871 B/op          1 allocs/op
PASS
ok      app     6.945s