Ex18.2-2 redundant DISK_READ

When the original root is split, suppose the new root is _s_, while the original root is _r_ and its sibling is _r'_. As in _B-TREE-INSERT_, _B-TREE-INSERT-NONFULL(s,k)_ is called, either _r_ or _r'_ will be read again, which is a redundant _DISK-READ_.