fix: add more optimizations to putMetacacheObject() (#12916)

- avoid extra lookup for 'xl.meta' since we are
  definitely sure that it doesn't exist.

- use this in newMultipartUpload() as well

- also additionally do not write with O_DSYNC
  to avoid loading the drives, instead create
  'xl.meta' for listing operations without
  O_DSYNC since these are ephemeral objects.

- do the same with newMultipartUpload() since
  it gets synced when the PutObjectPart() is
  attempted, we do not need to tax newMultipartUpload()
  instead.

cmd/xl-storage.go

@@ -953,6 +953,24 @@ func (s *xlStorage) UpdateMetadata(ctx context.Context, volume, path string, fi
 
 // WriteMetadata - writes FileInfo metadata for path at `xl.meta`
 func (s *xlStorage) WriteMetadata(ctx context.Context, volume, path string, fi FileInfo) error {
+	if fi.Fresh {
+		var xlMeta xlMetaV2
+		if err := xlMeta.AddVersion(fi); err != nil {
+			logger.LogIf(ctx, err)
+			return err
+		}
+		buf, err := xlMeta.AppendTo(nil)
+		if err != nil {
+			logger.LogIf(ctx, err)
+			return err
+		}
+		// First writes for special situations do not write to stable storage.
+		// this is currently used by
+		// - emphemeral objects such as objects created during listObjects() calls
+		// - newMultipartUpload() call..
+		return s.writeAll(ctx, volume, pathJoin(path, xlStorageFormatFile), buf, false)
+	}
+
 	buf, err := s.ReadAll(ctx, volume, pathJoin(path, xlStorageFormatFile))
 	if err != nil && err != errFileNotFound {
 		return err
@@ -1288,7 +1306,7 @@ func (s *xlStorage) ReadFile(ctx context.Context, volume string, path string, of
 	return int64(len(buffer)), nil
 }
 
-func (s *xlStorage) openFile(filePath string, mode int) (f *os.File, err error) {
+func (s *xlStorage) openFileSync(filePath string, mode int) (f *os.File, err error) {
 	// Create top level directories if they don't exist.
 	// with mode 0777 mkdir honors system umask.
 	if err = mkdirAll(pathutil.Dir(filePath), 0777); err != nil {
@@ -1315,6 +1333,33 @@ func (s *xlStorage) openFile(filePath string, mode int) (f *os.File, err error)
 	return w, nil
 }
 
+func (s *xlStorage) openFileNoSync(filePath string, mode int) (f *os.File, err error) {
+	// Create top level directories if they don't exist.
+	// with mode 0777 mkdir honors system umask.
+	if err = mkdirAll(pathutil.Dir(filePath), 0777); err != nil {
+		return nil, osErrToFileErr(err)
+	}
+
+	w, err := OpenFile(filePath, mode, 0666)
+	if err != nil {
+		// File path cannot be verified since one of the parents is a file.
+		switch {
+		case isSysErrIsDir(err):
+			return nil, errIsNotRegular
+		case osIsPermission(err):
+			return nil, errFileAccessDenied
+		case isSysErrIO(err):
+			return nil, errFaultyDisk
+		case isSysErrTooManyFiles(err):
+			return nil, errTooManyOpenFiles
+		default:
+			return nil, err
+		}
+	}
+
+	return w, nil
+}
+
 // To support O_DIRECT reads for erasure backends.
 type odirectReader struct {
 	f         *os.File
@@ -1525,7 +1570,7 @@ func (s *xlStorage) CreateFile(ctx context.Context, volume, path string, fileSiz
 	if fileSize >= 0 && fileSize <= smallFileThreshold {
 		// For streams smaller than 128KiB we simply write them as O_DSYNC (fdatasync)
 		// and not O_DIRECT to avoid the complexities of aligned I/O.
-		w, err := s.openFile(filePath, os.O_CREATE|os.O_WRONLY|os.O_EXCL)
+		w, err := s.openFileSync(filePath, os.O_CREATE|os.O_WRONLY|os.O_EXCL)
 		if err != nil {
 			return err
 		}
@@ -1585,7 +1630,7 @@ func (s *xlStorage) CreateFile(ctx context.Context, volume, path string, fileSiz
 	return nil
 }
 
-func (s *xlStorage) WriteAll(ctx context.Context, volume string, path string, b []byte) (err error) {
+func (s *xlStorage) writeAll(ctx context.Context, volume string, path string, b []byte, sync bool) (err error) {
 	volumeDir, err := s.getVolDir(volume)
 	if err != nil {
 		return err
@@ -1596,7 +1641,12 @@ func (s *xlStorage) WriteAll(ctx context.Context, volume string, path string, b
 		return err
 	}
 
-	w, err := s.openFile(filePath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC)
+	var w *os.File
+	if sync {
+		w, err = s.openFileSync(filePath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC)
+	} else {
+		w, err = s.openFileNoSync(filePath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC)
+	}
 	if err != nil {
 		return err
 	}
@@ -1614,6 +1664,10 @@ func (s *xlStorage) WriteAll(ctx context.Context, volume string, path string, b
 	return nil
 }
 
+func (s *xlStorage) WriteAll(ctx context.Context, volume string, path string, b []byte) (err error) {
+	return s.writeAll(ctx, volume, path, b, true)
+}
+
 // AppendFile - append a byte array at path, if file doesn't exist at
 // path this call explicitly creates it.
 func (s *xlStorage) AppendFile(ctx context.Context, volume string, path string, buf []byte) (err error) {
@@ -1642,7 +1696,7 @@ func (s *xlStorage) AppendFile(ctx context.Context, volume string, path string,
 	var w *os.File
 	// Create file if not found. Not doing O_DIRECT here to avoid the code that does buffer aligned writes.
 	// AppendFile() is only used by healing code to heal objects written in old format.
-	w, err = s.openFile(filePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY)
+	w, err = s.openFileSync(filePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY)
 	if err != nil {
 		return err
 	}