** 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 1.205 2004/11/05 00:43:12 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
**
**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
**     "Sorting And Searching", pages 473-480. Addison-Wesley
**     Publishing Company, Reading, Massachusetts.
................................................................................
  ** to a free page earlier in the file (somewhere before finSize).
  */
  for( iDbPage=finSize+1; iDbPage<=origSize; iDbPage++ ){
    rc = ptrmapGet(pBt, iDbPage, &eType, &iPtrPage);
    if( rc!=SQLITE_OK ) goto autovacuum_out;
    assert( eType!=PTRMAP_ROOTPAGE );

    /* If iDbPage is a free or pointer map page, do not swap it. */


    if( eType==PTRMAP_FREEPAGE || PTRMAP_ISPAGE(pgsz, iDbPage) ){
      continue;
    }
    rc = getPage(pBt, iDbPage, &pDbMemPage);
    if( rc!=SQLITE_OK ) goto autovacuum_out;

    /* Find the next page in the free-list that is not already at the end 
................................................................................
  rc = sqlite3pager_write(pPage1->aData);
  if( rc ) return rc;
  n = get4byte(&pPage1->aData[36]);
  put4byte(&pPage1->aData[36], n+1);

#ifndef SQLITE_OMIT_AUTOVACUUM
  /* If the database supports auto-vacuum, write an entry in the pointer-map
  ** to indicate that the page is free.

  */
  if( pBt->autoVacuum ){
    rc = ptrmapPut(pBt, pPage->pgno, PTRMAP_FREEPAGE, 0);



  }
#endif

  if( n==0 ){
    /* This is the first free page */
    rc = sqlite3pager_write(pPage->aData);
    if( rc ) return rc;
................................................................................
    Pgno pgnoMove;      /* Move a page here to make room for the root-page */
    MemPage *pPageMove; /* The page to move to. */

    /* Run the auto-vacuum code to ensure the free-list is empty. This is
    ** not really necessary, but it avoids complications in dealing with
    ** a free-list in the code below.
    ** TODO: This may need to be revisited.



    */

    rc = autoVacuumCommit(pBt);
    if( rc!=SQLITE_OK ) return rc;


    /* Read the value of meta[3] from the database to determine where the
    ** root page of the new table should go. meta[3] is the largest root-page
    ** created so far, so the new root-page is (meta[3]+1).
    */
    rc = sqlite3BtreeGetMeta(pBt, 4, &pgnoRoot);
    if( rc!=SQLITE_OK ) return rc;
................................................................................
    }
    assert( pgnoRoot>=3 );

    /* Allocate a page. The page that currently resides at pgnoRoot will
    ** be moved to the allocated page (unless the allocated page happens
    ** to reside at pgnoRoot).
    */
    rc = allocatePage(pBt, &pPageMove, &pgnoMove, 0);
    if( rc!=SQLITE_OK ){
      return rc;
    }

    if( pgnoMove!=pgnoRoot ){
      u8 eType;
      Pgno iPtrPage;
................................................................................
      releasePage(pPageMove);
      rc = getPage(pBt, pgnoRoot, &pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = ptrmapGet(pBt, pgnoRoot, &eType, &iPtrPage);
      assert( eType!=PTRMAP_ROOTPAGE );

      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
      }
      rc = relocatePage(pBt, pRoot, eType, iPtrPage, pgnoMove);
      releasePage(pRoot);
      if( rc!=SQLITE_OK ){

** 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 1.206 2004/11/05 01:45:14 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** For a detailed discussion of BTrees, refer to
**
**     Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3:
**     "Sorting And Searching", pages 473-480. Addison-Wesley
**     Publishing Company, Reading, Massachusetts.
................................................................................
  ** to a free page earlier in the file (somewhere before finSize).
  */
  for( iDbPage=finSize+1; iDbPage<=origSize; iDbPage++ ){
    rc = ptrmapGet(pBt, iDbPage, &eType, &iPtrPage);
    if( rc!=SQLITE_OK ) goto autovacuum_out;
    assert( eType!=PTRMAP_ROOTPAGE );

    /* If iDbPage is a free or pointer map page, do not swap it.
    ** Instead, make sure the page is in the journal file.
    */
    if( eType==PTRMAP_FREEPAGE || PTRMAP_ISPAGE(pgsz, iDbPage) ){
      continue;
    }
    rc = getPage(pBt, iDbPage, &pDbMemPage);
    if( rc!=SQLITE_OK ) goto autovacuum_out;

    /* Find the next page in the free-list that is not already at the end 
................................................................................
  rc = sqlite3pager_write(pPage1->aData);
  if( rc ) return rc;
  n = get4byte(&pPage1->aData[36]);
  put4byte(&pPage1->aData[36], n+1);

#ifndef SQLITE_OMIT_AUTOVACUUM
  /* If the database supports auto-vacuum, write an entry in the pointer-map
  ** to indicate that the page is free. Also make sure the page is in
  ** the journal file.
  */
  if( pBt->autoVacuum ){
    rc = ptrmapPut(pBt, pPage->pgno, PTRMAP_FREEPAGE, 0);
    if( rc ) return rc;
    rc = sqlite3pager_write(pPage->aData);
    if( rc ) return rc;
  }
#endif

  if( n==0 ){
    /* This is the first free page */
    rc = sqlite3pager_write(pPage->aData);
    if( rc ) return rc;
................................................................................
    Pgno pgnoMove;      /* Move a page here to make room for the root-page */
    MemPage *pPageMove; /* The page to move to. */

    /* Run the auto-vacuum code to ensure the free-list is empty. This is
    ** not really necessary, but it avoids complications in dealing with
    ** a free-list in the code below.
    ** TODO: This may need to be revisited.
    ** TODO2: Actually this is no-good. running the auto-vacuum routine
    **        involves truncating the database, which means the journal-file
    **        must be synced(). No-good.
    */
/*
    rc = autoVacuumCommit(pBt);
    if( rc!=SQLITE_OK ) return rc;
*/

    /* Read the value of meta[3] from the database to determine where the
    ** root page of the new table should go. meta[3] is the largest root-page
    ** created so far, so the new root-page is (meta[3]+1).
    */
    rc = sqlite3BtreeGetMeta(pBt, 4, &pgnoRoot);
    if( rc!=SQLITE_OK ) return rc;
................................................................................
    }
    assert( pgnoRoot>=3 );

    /* Allocate a page. The page that currently resides at pgnoRoot will
    ** be moved to the allocated page (unless the allocated page happens
    ** to reside at pgnoRoot).
    */
    rc = allocatePage(pBt, &pPageMove, &pgnoMove, 1);
    if( rc!=SQLITE_OK ){
      return rc;
    }

    if( pgnoMove!=pgnoRoot ){
      u8 eType;
      Pgno iPtrPage;
................................................................................
      releasePage(pPageMove);
      rc = getPage(pBt, pgnoRoot, &pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = ptrmapGet(pBt, pgnoRoot, &eType, &iPtrPage);
      assert( eType!=PTRMAP_ROOTPAGE );
      assert( eType!=PTRMAP_FREEPAGE );
      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
      }
      rc = relocatePage(pBt, pRoot, eType, iPtrPage, pgnoMove);
      releasePage(pRoot);
      if( rc!=SQLITE_OK ){