storage/buffer.go
func (b *BufferedSeriesIterator) Next() bool {
	if !b.ok {
		return false
	}

	// Add current element to buffer before advancing.
	b.buf.add(b.it.At())

	b.ok = b.it.Next()
	if b.ok {
		b.lastTime, _ = b.Values()
	}

	return b.ok
}
func (b *BufferedSeriesIterator) Next() bool {
	if !b.ok {
		return false
	}

	// Add current element to buffer before advancing.
	b.buf.add(b.it.At())

	b.ok = b.it.Next()
	if b.ok {
		b.lastTime, _ = b.Values()
	}

	return b.ok
}
// Next advances the iterator to the next element.