func (s *Snapshotter) DBFilePath(id uint64) (string, error) {
	if _, err := fileutil.ReadDir(s.dir); err != nil {
		return "", err
	}
	fn := s.dbFilePath(id)
	if fileutil.Exist(fn) {
		return fn, nil
	}
	if s.lg != nil {
		s.lg.Warn(
			"failed to find [SNAPSHOT-INDEX].snap.db",
			zap.Uint64("snapshot-index", id),
			zap.String("snapshot-file-path", fn),
			zap.Error(ErrNoDBSnapshot),
		)
	}
	return "", ErrNoDBSnapshot
}
func (s *Snapshotter) DBFilePath(id uint64) (string, error) {
	if _, err := fileutil.ReadDir(s.dir); err != nil {
		return "", err
	}
	fn := s.dbFilePath(id)
	if fileutil.Exist(fn) {
		return fn, nil
	}
	if s.lg != nil {
		s.lg.Warn(
			"failed to find [SNAPSHOT-INDEX].snap.db",
			zap.Uint64("snapshot-index", id),
			zap.String("snapshot-file-path", fn),
			zap.Error(ErrNoDBSnapshot),
		)
	}
	return "", ErrNoDBSnapshot
}
// DBFilePath returns the file path for the snapshot of the database with
// given id. If the snapshot does not exist, it returns error.