func NewV3(lg *zap.Logger) Manager {
	if lg == nil {
		lg = zap.NewExample()
	}
	return &v3Manager{lg: lg}
}
func NewV3(lg *zap.Logger) Manager {
	if lg == nil {
		lg = zap.NewExample()
	}
	return &v3Manager{lg: lg}
}
// NewV3 returns a new snapshot Manager for v3.x snapshot.