heap = heap[:len(heap)-1]
	// Sift the root down.
	heapSiftDown(heap, 0)
	return heap
}

func heapSiftUp(heap []*batchCursor, i int) int {
	for i > 0 && heap[(i-1)/2].ev.time > heap[i].ev.time {
		heap[(i-1)/2], heap[i] = heap[i], heap[(i-1)/2]
		i = (i - 1) / 2
	}
	return i
}

func heapSiftDown(heap []*batchCursor, i int) int {
	for {
		m := min3(heap, i, 2*i+1, 2*i+2)