func (b *BufferedSeriesIterator) Reset(it chunkenc.Iterator) {
	b.it = it
	b.lastTime = math.MinInt64
	b.ok = true
	b.buf.reset()
	b.buf.delta = b.delta
	it.Next()
}
Reset re-uses the buffer with a new iterator, resetting the buffered time
delta to its original value.
package storage
import (
	"math"
	"github.com/prometheus/prometheus/tsdb/chunkenc"
)
type BufferedSeriesIterator struct {
	it    chunkenc.Iterator
	buf   *sampleRing
	delta int64
	lastTime int64
	ok       bool
}
func NewBuffer(delta int64) *BufferedSeriesIterator {
	return NewBufferIterator(chunkenc.NewNopIterator(), delta)
}
func NewBufferIterator(it chunkenc.Iterator, delta int64) *BufferedSeriesIterator {
	bit := &BufferedSeriesIterator{
		buf:   newSampleRing(delta, 16),
		delta: delta,
	}
	bit.Reset(it)
	return bit
}