mvcc/backend/tx_buffer.go
func (bb *bucketBuffer) merge(bbsrc *bucketBuffer) {
	for i := 0; i < bbsrc.used; i++ {
		bb.add(bbsrc.buf[i].key, bbsrc.buf[i].val)
	}
	if bb.used == bbsrc.used {
		return
	}
	if bytes.Compare(bb.buf[(bb.used-bbsrc.used)-1].key, bbsrc.buf[0].key) < 0 {
		return
	}

	sort.Stable(bb)

	// remove duplicates, using only newest update
	widx := 0
	for ridx := 1; ridx < bb.used; ridx++ {
		if !bytes.Equal(bb.buf[ridx].key, bb.buf[widx].key) {
			widx++
		}
		bb.buf[widx] = bb.buf[ridx]
	}
	bb.used = widx + 1
}
func (bb *bucketBuffer) merge(bbsrc *bucketBuffer) {
	for i := 0; i < bbsrc.used; i++ {
		bb.add(bbsrc.buf[i].key, bbsrc.buf[i].val)
	}
	if bb.used == bbsrc.used {
		return
	}
	if bytes.Compare(bb.buf[(bb.used-bbsrc.used)-1].key, bbsrc.buf[0].key) < 0 {
		return
	}

	sort.Stable(bb)

	// remove duplicates, using only newest update
	widx := 0
	for ridx := 1; ridx < bb.used; ridx++ {
		if !bytes.Equal(bb.buf[ridx].key, bb.buf[widx].key) {
			widx++
		}
		bb.buf[widx] = bb.buf[ridx]
	}
	bb.used = widx + 1
}
// merge merges data from bb into bbsrc.