SQLite

/*
** 2004 April 6
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.522 2008/09/30 14:06:29 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

        ** node above may have modified the structure of the B-Tree and
        ** so the current contents of leafCur.apPage[] and leafCur.aiIdx[]
        ** may not be trusted.
        **
        ** It is not possible to copy the ancestry from pCur, as the same
        ** balance() call has invalidated the pCur->apPage[] and aiIdx[]
        ** arrays. 
        **
        ** The call to saveCursorPosition() below internally saves the 
        ** key that leafCur is currently pointing to. Currently, there
        ** are two copies of that key in the tree - one here on the leaf
        ** page and one on some internal node in the tree. The copy on
        ** the leaf node is always the next key in tree-order after the 
        ** copy on the internal node. So, the call to sqlite3BtreeNext()
        ** calls restoreCursorPosition() to point the cursor to the copy
        ** stored on the internal node, then advances to the next entry,
        ** which happens to be the copy of the key on the internal node.
        ** Net effect: leafCur is pointing back where
        */
      #ifndef NDEBUG
        Pgno leafPgno = pLeafPage->pgno;
      #endif
        rc = saveCursorPosition(&leafCur);
        if( rc==SQLITE_OK ){
          rc = sqlite3BtreeNext(&leafCur, &notUsed);