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 1.203 2004/11/04 02:57:34 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.

  data[20] = pBt->pageSize - pBt->usableSize;
  data[21] = pBt->maxEmbedFrac;
  data[22] = pBt->minEmbedFrac;
  data[23] = pBt->minLeafFrac;
  memset(&data[24], 0, 100-24);
  zeroPage(pP1, PTF_INTKEY|PTF_LEAF|PTF_LEAFDATA );
  pBt->pageSizeFixed = 1;
#ifndef SQLITE_OMIT_AUTOVACUUM
  if( pBt->autoVacuum ){
    put4byte(&data[36 + 4*4], 1);
  }
#endif
  return SQLITE_OK;
}

/*
** Attempt to start a new transaction. A write-transaction
** is started if the second argument is nonzero, otherwise a read-
** transaction.  If the second argument is 2 or more and exclusive

      put4byte(&pPage->aData[pPage->hdrOffset+8], iTo);
    }

    pPage->isInit = isInitOrig;
  }
}


static int relocatePage(
  Btree *pBt, 
  MemPage *pDbPage,
  u8 eType,
  Pgno iPtrPage,
  Pgno iFreePage
){
  MemPage *pPtrPage;   /* The page that contains a pointer to pDbPage */
  Pgno iDbPage = pDbPage->pgno;
  Pager *pPager = pBt->pPager;
  int rc;

  assert( eType==PTRMAP_OVERFLOW2 
      || eType==PTRMAP_OVERFLOW1 || eType==PTRMAP_BTREE );

  /* Move page iDbPage from it's current location to page number iFreePage */
  TRACE(("AUTOVACUUM: Moving %d to free page %d (ptr page %d type %d)\n", 
      iDbPage, iFreePage, iPtrPage, eType));
  rc = sqlite3pager_movepage(pPager, pDbPage->aData, iFreePage);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  pDbPage->pgno = iFreePage;

  /* If pDbPage was a btree-page, then it may have child pages and/or cells
  ** that point to overflow pages. The pointer map entries for all these
  ** pages need to be changed.
  **
  ** If pDbPage is an overflow page, then the first 4 bytes may store a
  ** pointer to a subsequent overflow page. If this is the case, then
  ** the pointer map needs to be updated for the subsequent overflow page.
  */
  if( eType==PTRMAP_BTREE ){
    rc = setChildPtrmaps(pDbPage);
    if( rc!=SQLITE_OK ){
      return rc;
    }
  }else{
    Pgno nextOvfl = get4byte(pDbPage->aData);
    if( nextOvfl!=0 ){
      assert( nextOvfl<=sqlite3pager_pagecount(pPager) );
      rc = ptrmapPut(pBt, nextOvfl, PTRMAP_OVERFLOW2, iFreePage);
      if( rc!=SQLITE_OK ){
        return rc;
      }
    }
  }

  /* Fix the database pointer on page iPtrPage that pointed at iDbPage so
  ** that it points at iFreePage. Also fix the pointer map entry for
  ** iPtrPage.
  */
  rc = getPage(pBt, iPtrPage, &pPtrPage);
  if( rc!=SQLITE_OK ){
    return rc;
  }
  rc = sqlite3pager_write(pPtrPage->aData);
  if( rc!=SQLITE_OK ){
    releasePage(pPtrPage);
    return rc;
  }
  modifyPagePointer(pPtrPage, iDbPage, iFreePage, eType);
  rc = ptrmapPut(pBt, iFreePage, eType, iPtrPage);
  releasePage(pPtrPage);
  return rc;
}

/* Forward declaration required by autoVacuumCommit(). */
static int allocatePage(Btree *, MemPage **, Pgno *, Pgno);

/*
** This routine is called prior to sqlite3pager_commit when a transaction
** is commited for an auto-vacuum database.
*/
static int autoVacuumCommit(Btree *pBt){
  Pager *pPager = pBt->pPager;
  Pgno nFreeList;   /* Number of pages remaining on the free-list. */
  int nPtrMap;      /* Number of pointer-map pages deallocated */
  Pgno origSize;  /* Pages in the database file */
  Pgno finSize;   /* Pages in the database file after truncation */
  int i;            /* Counter variable */
  int rc;           /* Return code */
  u8 eType;
  int pgsz = pBt->pageSize;  /* Page size for this database */
  Pgno iDbPage;              /* The database page to move */

  MemPage *pDbMemPage = 0;   /* "" */
  Pgno iPtrPage;             /* The page that contains a pointer to iDbPage */

  Pgno iFreePage;            /* The free-list page to move iDbPage to */
  MemPage *pFreeMemPage = 0; /* "" */

#ifndef NDEBUG
  int nRef = *sqlite3pager_stats(pPager);
#endif

    /* 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 
    ** of the file. A page can be pulled off the free list using the 
    ** allocatePage() routine.
    */
    do{
      if( pFreeMemPage ){
        releasePage(pFreeMemPage);
        pFreeMemPage = 0;
      }
      rc = allocatePage(pBt, &pFreeMemPage, &iFreePage, 0);
      if( rc!=SQLITE_OK ) goto autovacuum_out;
      assert( iFreePage<=origSize );
    }while( iFreePage>finSize );




    releasePage(pFreeMemPage);
    pFreeMemPage = 0;













    rc = relocatePage(pBt, pDbMemPage, eType, iPtrPage, iFreePage);









    releasePage(pDbMemPage);







    if( rc!=SQLITE_OK ) goto autovacuum_out;






  }

  /* The entire free-list has been swapped to the end of the file. So
  ** truncate the database file to finSize pages and consider the
  ** free-list empty.
  */
  rc = sqlite3pager_write(pBt->pPage1->aData);

**     BTREE_INTKEY|BTREE_LEAFDATA     Used for SQL tables with rowid keys
**     BTREE_ZERODATA                  Used for SQL indices
*/
int sqlite3BtreeCreateTable(Btree *pBt, int *piTable, int flags){
  MemPage *pRoot;
  Pgno pgnoRoot;
  int rc;
/* TODO: Disallow schema modifications if there are open cursors */
  if( pBt->inTrans!=TRANS_WRITE ){
    /* Must start a transaction first */
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  if( pBt->readOnly ){
    return SQLITE_READONLY;
  }
#ifdef SQLITE_OMIT_AUTOVACUUM
  rc = allocatePage(pBt, &pRoot, &pgnoRoot, 1);
  if( rc ) return rc;
#else
  if( pBt->autoVacuum ){
    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;
    pgnoRoot++;

    /* The new root-page may not be allocated on a pointer-map page. */
    if( pgnoRoot==PTRMAP_PAGENO(pBt->pageSize, pgnoRoot) ){
      pgnoRoot++;
    }
    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);
      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
      }
      rc = relocatePage(pBt, pRoot, eType, iPtrPage, pgnoMove);
      releasePage(pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = getPage(pBt, pgnoRoot, &pRoot);
      if( rc!=SQLITE_OK ){
        return rc;
      }
      rc = sqlite3pager_write(pRoot->aData);
      if( rc!=SQLITE_OK ){
        releasePage(pRoot);
        return rc;
      }
    }else{
      pRoot = pPageMove;
    } 

    rc = ptrmapPut(pBt, pgnoRoot, PTRMAP_ROOTPAGE, 0);
    if( rc ){
      releasePage(pRoot);
      return rc;
    }
    rc = sqlite3BtreeUpdateMeta(pBt, 4, pgnoRoot);
    if( rc ){
      releasePage(pRoot);
      return rc;
    }
  }else{
    rc = allocatePage(pBt, &pRoot, &pgnoRoot, 1);
    if( rc ) return rc;
  }
#endif
  assert( sqlite3pager_iswriteable(pRoot->aData) );
  zeroPage(pRoot, flags | PTF_LEAF);
  sqlite3pager_unref(pRoot->aData);
  *piTable = (int)pgnoRoot;
  return SQLITE_OK;

** This routine will fail with SQLITE_LOCKED if there are any open
** cursors on the table.
*/
int sqlite3BtreeDropTable(Btree *pBt, int iTable){
  int rc;
  MemPage *pPage;
  BtCursor *pCur;
/* TODO: Disallow schema modifications if there are open cursors */
  if( pBt->inTrans!=TRANS_WRITE ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    if( pCur->pgnoRoot==(Pgno)iTable ){
      return SQLITE_LOCKED;  /* Cannot drop a table that has a cursor */
    }

  rc = sqlite3pager_get(pBt->pPager, 1, (void**)&pP1);
  if( rc ) return rc;
  *pMeta = get4byte(&pP1[36 + idx*4]);
  sqlite3pager_unref(pP1);

  /* The current implementation is unable to handle writes to an autovacuumed
  ** database.  So make such a database readonly. */
#ifdef SQLITE_OMIT_AUTOVACUUM
  if( idx==4 && *pMeta>0 ) pBt->readOnly = 1;
#endif

  return SQLITE_OK;
}

/*
** Write meta-information back into the database.  Meta[0] is
** read-only and may not be written.

# 2001 September 15
#
# 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.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the SELECT statement.
#
# $Id: autovacuum.test,v 1.5 2004/11/04 02:57:35 danielk1977 Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Return a string $len characters long. The returned string is $char repeated
# over and over. For example, [make_str abc 8] returns "abcabcab".
proc make_str {char len} {

  }

  # All rows have been deleted. Ensure the file has shrunk to 4 pages.
  do_test autovacuum-1.$tn.3 {
    file_pages
  } {4}
}

# Tests autovacuum-2.* test that root pages are allocated correctly at
# the start of the file.
do_test autovacuum-2.1 {
  for {set i 0} {$i<5} {incr i} {
    execsql "
      INSERT INTO av1 VALUES('[make_str abc 1000]')
    "
  }
  file_pages 
} {14}

for {set i 5} {$i < 15} {incr i} {
  set tablename "av$i"
  
  do_test autovacuum-2.$i.2 {
    execsql "
      CREATE TABLE $tablename (a);
      SELECT rootpage FROM sqlite_master WHERE name = '$tablename';
    "
  } $i

  do_test autovacuum-2.$i.3 {
    file_pages 
  } [expr $i+10]

  do_test autovacuum-2.$i.4 {
    execsql {
      pragma integrity_check
    }
  } {ok}
}


finish_test