skiplist/merger.go
func (mit *MergeIterator) SeekFirst() {
	for _, it := range mit.iters {
		it.SeekFirst()
		if it.Valid() {
			n := it.GetNode()
			mit.h = append(mit.h, heapItem{iter: it, n: n})
		}
	}

	heap.Init(&mit.h)
	mit.Next()
}
func (mit *MergeIterator) SeekFirst() {
	for _, it := range mit.iters {
		it.SeekFirst()
		if it.Valid() {
			n := it.GetNode()
			mit.h = append(mit.h, heapItem{iter: it, n: n})
		}
	}

	heap.Init(&mit.h)
	mit.Next()
}
// SeekFirst moves cursor to the first item