storage/remote/write.go
func (t *timestampTracker) AddFast(l labels.Labels, _ uint64, ts int64, v float64) error {
	_, err := t.Add(l, ts, v)
	return err
}
func (t *timestampTracker) AddFast(l labels.Labels, _ uint64, ts int64, v float64) error {
	_, err := t.Add(l, ts, v)
	return err
}
// AddFast implements storage.Appender.