Is this a bug in Database System Concepts 6th edition-Figure 11.11 Querying a B+-tree.-procedure printAll(value V)?

Question

In Database System Concepts, 6 ^th edition, chapter 11, in "Figure 11.11 Querying a B+-tree.", there is a procedure printAll(value V) . It is used to print all records with search key value V (there can be duplicates). It calls find(V) , which returns the first leaf node that has key V , and the first index i in that leaf that has that key.

Why doesn't the code include Set i = 1 when i > number of keys in L ?

procedure printAll( value V )
/* prints all records with search key value V */
Set done = false;
Set ( L,i ) = find( V );
if (( L,i ) is null) return
repeat
repeat
Print record pointed to by L.P _i
Set i = i + 1
until ( i > number of keys in L or LK _i > V )
if ( i > number of keys in L )
then L = LP _n // No need to set i to 1?
else Set done = true;
until (done or L is null)

Answer 1

You are absolutely right. i needs to be reset to 1 when moving to the next leaf in the B+ tree.

It is also not corrected in the "Errata and Updates For Database System Concepts, 6 ^th Edition"

There is a C++ implementation on github , inspired by this book, which does reset i as it should have been. Of course, in C++ indexes are zero-based:

void BPlusTree::printAll(string v) {
    //
    // B+ tree described in the book may contain duplicate keys
    // printAl prints all the records with key v
    // but here I modified it to print all records with key >= v
    //
    bool done = false;
    auto pair = find(v);
    auto p = pair.first;
    auto i = pair.second;
    if (i == -1) {  // not found
        cout << "no such record" << endl;
        return;
    }
    cout << "i is " << i << endl;
    while (!done and p != NULL) {
         // be careful with special cases, may encounter NULL pointer, size is also a problem (#pointer = #key + 1)
        for (; (i < p->_ptrs.size() && i < p->_keys.size() && v <= p->_keys[i]) or (i == p->_keys.size()); i++) {
            if (p->_ptrs[i] == NULL) {
                continue;
            }
            cout << "record: " << *reinterpret_cast<int*>(p->_ptrs[i]) << endl;
        }
        if (i >= _num_of_keys(p)) {
            p = p->_next;  // move to next leaf node
            i = 0;  // adjust i
        }
        else {
            done = true;
        }
    }
}