Benchmark fdatasync vs fsync

fdatasync_vs_fsync.go

package main

import (
	"log"
	"math/rand"
	"os"
	"syscall"
	"testing"
	"time"

	"golang.org/x/sys/unix"
)

const theFile = "/tmp/theFileBenchMarkFile.txt"
const fSize = 50 * 1024 * 1024 // 50Mb

func randString(length int) []byte {
	var source = rand.NewSource(time.Now().UnixNano())
	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	b := make([]byte, length)
	for i := range b {
		b[i] = charset[source.Int63()%int64(len(charset))]
	}
	return b
}

func fsync_stdlib() {
	f, err := os.Create(theFile)
	if err != nil {
		log.Fatalln("unable to open file:", err)
	}

	_, err = f.Write(randString(fSize))
	if err != nil {
		log.Fatalln("unable to write to file:", err)
	}

	err = f.Sync()
	if err != nil {
		log.Fatalln("unable to Sync file:", err)
	}

	err = f.Close()
	if err != nil {
		log.Fatalln("unable to Close file:", err)
	}
}
func fsync_x_sys() {
	f, err := os.Create(theFile)
	if err != nil {
		log.Fatalln("unable to open file:", err)
	}

	_, err = f.Write(randString(fSize))
	if err != nil {
		log.Fatalln("unable to write to file:", err)
	}

	err = unix.Fsync(int(f.Fd()))
	if err != nil {
		log.Fatalln("unable to Sync file:", err)
	}

	err = f.Close()
	if err != nil {
		log.Fatalln("unable to Close file:", err)
	}
}

func fdatasync_stdlib() {
	f, err := os.Create(theFile)
	if err != nil {
		log.Fatalln("unable to open file:", err)
	}

	_, err = f.Write(randString(fSize))
	if err != nil {
		log.Fatalln("unable to write to file:", err)
	}

	// fdatasync() [...] does not flush modified metadata unless that metadata is needed in order to allow a subsequent data retrieval to be correctly handled. [...]
	// On the other hand, a change to the file size (st_size, as made by say ftruncate(2)), would require a metadata flush.
	//
	// Note: sync of file does not also sync its directory.
	// The directory needs to also be synced
	err = syscall.Fdatasync(int(f.Fd()))
	if err != nil {
		log.Fatalln("unable to Fdatasync file:", err)
	}

	err = f.Close()
	if err != nil {
		log.Fatalln("unable to Close file:", err)
	}
}

func fdatasync_x_sys() {
	f, err := os.Create(theFile)
	if err != nil {
		log.Fatalln("unable to open file:", err)
	}

	_, err = f.Write(randString(fSize))
	if err != nil {
		log.Fatalln("unable to write to file:", err)
	}

	err = unix.Fdatasync(int(f.Fd()))
	if err != nil {
		log.Fatalln("unable to Fdatasync file:", err)
	}

	err = f.Close()
	if err != nil {
		log.Fatalln("unable to Close file:", err)
	}
}

func removeFile() {
	_ = os.Remove(theFile)
}

func BenchmarkFSync_stdlib(b *testing.B) {
	removeFile()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		fsync_stdlib()
	}
}

func BenchmarkFSync_x_sys(b *testing.B) {
	removeFile()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		fsync_x_sys()
	}
}

func BenchmarkFDataSync_stdlib(b *testing.B) {
	removeFile()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		fdatasync_stdlib()
	}
}

func BenchmarkFDataSync_x_sys(b *testing.B) {
	removeFile()
	b.ResetTimer()
	for i := 0; i < b.N; i++ {
		fdatasync_x_sys()
	}
}

go test -timeout 10m -v -race -cover -bench=. -run=XXX ./...

BenchmarkFSync_stdlib-4       	       1	13182840400 ns/op.   // 13_182_840_400 ns/op
BenchmarkFSync_x_sys-4        	       1	13364355200 ns/op.   // 13_364_355_200 ns/op
BenchmarkFDataSync_stdlib-4   	       1	13715179700 ns/op.   // 13_715_179_700 ns/op
BenchmarkFDataSync_x_sys-4    	       1	13434866000 ns/op.   // 13_434_866_000 ns/op