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 1.108 2004/05/03 19:49:33 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.

  data = pPage->aData;
  assert( sqlitepager_iswriteable(data->aData) );
  assert( pPage->pBt );
  if( nByte<4 ) nByte = 4;
  if( pPage->nFree<nByte || pPage->isOverfull ) return 0;
  hdr = pPage->hdrOffset;
  if( data[hdr+5]>=60 ){
    defragmentPage(pPage);
  }
  addr = hdr+1;
  pc = get2byte(&data[addr]);
  assert( addr<pc );
  assert( pc<=pPage->pageSize-4 );
  while( (size = get2byte(&data[pc+2]))<nByte ){

** to start a new checkpoint if another checkpoint is already active.
*/
int sqlite3BtreeBeginStmt(Btree *pBt){
  int rc;
  if( !pBt->inTrans || pBt->inStmt ){
    return pBt->readOnly ? SQLITE_READONLY : SQLITE_ERROR;
  }
  rc = pBt->readOnly ? SQLITE_OK : sqlitepager_stmt_begin(pBt->pPager);
  pBt->inStmt = 1;
  return rc;
}


/*
** Commit a checkpoint to transaction currently in progress.  If no
** checkpoint is active, this is a no-op.
*/
int sqlite3BtreeCommitStmt(Btree *pBt){
  int rc;
  if( pBt->inStmt && !pBt->readOnly ){
    rc = sqlitepager_stmt_commit(pBt->pPager);
  }else{
    rc = SQLITE_OK;
  }
  pBt->inStmt = 0;
  return rc;
}

/*
** Rollback the checkpoint to the current transaction.  If there
** is no active checkpoint or transaction, this routine is a no-op.
**
** All cursors will be invalided by this operation.  Any attempt
** to use a cursor that was open at the beginning of this operation
** will result in an error.
*/
int sqlite3BtreeRollbackStmt(Btree *pBt){
  int rc;
  BtCursor *pCur;
  if( pBt->inStmt==0 || pBt->readOnly ) return SQLITE_OK;
  rc = sqlitepager_stmt_rollback(pBt->pPager);
  for(pCur=pBt->pCursor; pCur; pCur=pCur->pNext){
    MemPage *pPage = pCur->pPage;
    if( pPage && !pPage->isInit ){
      releasePage(pPage);
      pCur->pPage = 0;
    }
  }

  int rc;
  int n;     /* Number of pages on the freelist */
  int k;     /* Number of leaves on the trunk of the freelist */

  pPage1 = pBt->pPage1;
  n = get4byte(&pPage1->aData[36]);
  if( n>0 ){
    /* There are pages on the freelist.  Reuse one of those pages. */
    MemPage *pTrunk;
    rc = sqlitepager_write(pPage1->aData);
    if( rc ) return rc;
    put4byte(&pPage1->aData[36], n-1);
    rc = getPage(pBt, get4byte(&pPage1->aData[32]), &pTrunk);
    if( rc ) return rc;
    rc = sqlitepager_write(pTrunk->aData);

    if( rc ) return rc;
    sqlitepager_unref(pOvfl->aData);
  }
  return SQLITE_OK;
}

/*
** Create the byte sequence used to represent a cell on page pPage
** and write that byte sequence into pCell[].  Overflow pages are
** allocated and filled in as necessary.  The calling procedure
** is responsible for making sure sufficient space has been allocated
** for pCell[].
**

** Note that pCell does not necessary need to point to the pPage->aData




** area.  pCell might point to some temporary storage.  The cell will







** be constructed in this temporary area then copied into pPage->aData
** later.



*/
static int fillInCell(
  MemPage *pPage,                /* The page that contains the cell */
  unsigned char *pCell,          /* Complete text of the cell */
  const void *pKey, u64 nKey,    /* The key */
  const void *pData,int nData,   /* The data */
  int *pnSize                    /* Write cell size here */
){
  int nPayload;
  const void *pSrc;
  int nSrc, nSrc2;
  int spaceLeft;
  MemPage *pOvfl = 0;
  unsigned char *pPrior;
  unsigned char *pPayload;
  Btree *pBt = pPage->pBt;
  Pgno pgnoOvfl = 0;
  int nHeader;

  /* Fill in the header. */
  nHeader = 2;
  if( !pPage->leaf ){
    nHeader += 4;
  }
  if( !pPage->zeroData ){
    nHeader += putVarint(&pCell[nHeader], nData);
  }
  nHeader += putVarint(&pCell[nHeader], nKey);
  
  /* Fill in the payload */
  if( pPage->zeroData ){
    nData = 0;
  }
  nPayload = nData;
  if( pPage->intKey ){
    pSrc = pData;
    nSrc = nData;
    nData = 0;
  }else{
    nPayload += nKey;
    pSrc = pKey;
    nSrc = nKey;
  }
  if( nPayload>pBt->maxLocal ){
    *pnSize = nHeader + pBt->maxLocal + 4;

    put2byte(&pPage->aData[idxFrom], idx);
    idxFrom = idx;
  }
  put2byte(&pPage->aData[idxFrom], 0);
}

/*
** Move the content of the page at pFrom over to pTo.  The pFrom->aCell[]
** pointers that point into pFrom->aData[] must be adjusted to point
** into pTo->aData[] instead.  But some pFrom->aCell[] entries might
** not point to pFrom->aData[].  Those are unchanged.
**
** Over this operation completes, the meta data for pFrom is zeroed.
*/
static void copyPage(MemPage *pTo, MemPage *pFrom){
  uptr from, to;
  int i;
  int pageSize;
  int ofst;

  assert( pTo->hdrOffset==0 );
  ofst = pFrom->hdrOffset;
  pageSize = pTo->pBt->pageSize;
  sqliteFree(pTo->aCell);
  memcpy(pTo->aData, &pFrom->aData[ofst], pageSize - ofst + sizeof(MemPage));



  memset(pFrom, 0, sizeof(MemPage));

  assert( pTo->aData[5]<155 );
  pTo->aData[5] += ofst;
  pTo->isOverfull = pFrom->isOverfull;
  to = Addr(pTo->aData);
  from = Addr(&pFrom->aData[ofst]);
  for(i=0; i<pTo->nCell; i++){
    uptr x = Addr(pTo->aCell[i]);
    if( x>from && x<from+pageSize-ofst ){
      *((uptr*)&pTo->aCell[i]) = x + to - from;


    }
  }
}

/*
** The following parameters determine how many adjacent pages get involved
** in a balancing operation.  NN is the number of neighbors on either side

  int nNew;                    /* Number of pages in apNew[] */
  int nDiv;                    /* Number of cells in apDiv[] */
  int i, j, k;                 /* Loop counters */
  int idx;                     /* Index of pPage in pParent->apCell[] */
  int nxDiv;                   /* Next divider slot in pParent->apCell[] */
  int rc;                      /* The return code */
  int iCur;                    /* apCell[iCur] is the cell of the cursor */
  int leafCorrection;          /* 4 if pPage is a leaf.  0 if not */
  int usableSpace;             /* Bytes in pPage beyond the header */
  int pageFlags;               /* Value of pPage->aData[0] */
  MemPage *pOldCurPage;        /* The cursor originally points to this page */
  int subtotal;                /* Subtotal of bytes in cells on one page */
  MemPage *apOld[NB];          /* pPage and up to two siblings */
  Pgno pgnoOld[NB];            /* Page numbers for each page in apOld[] */
  MemPage *apCopy[NB];         /* Private copies of apOld[] pages */
  MemPage *apNew[NB+1];        /* pPage and up to NB siblings after balancing */
  Pgno pgnoNew[NB+1];          /* Page numbers for each page in apNew[] */

      break;
    }
    rc = getPage(pBt, pgnoOld[i], &apOld[i]);
    if( rc ) goto balance_cleanup;
    rc = initPage(apOld[i], pParent);
    if( rc ) goto balance_cleanup;
    apOld[i]->idxParent = k;
    apCopy[i] = 0;
    assert( i==nOld );
    nOld++;
  }

  /*
  ** Make copies of the content of pPage and its siblings into aOld[].
  ** The rest of this function will use data from the copies rather
  ** that the original pages since the original pages will be in the

  rc = balance(pParent);

  /*
  ** Cleanup before returning.
  */
balance_cleanup:
  for(i=0; i<nOld; i++){
    releasePage(apOld[i]);
    if( apCopy[i] ){
      releasePage(apCopy[i]->pParent);
      sqliteFree(apCopy[i]->aCell);
    }
  }
  for(i=0; i<nNew; i++){
    releasePage(apNew[i]);
  }
  releasePage(pParent);
  return rc;
}

/*
** This routine checks all cursors that point to the same table
** as pCur points to.  If any of those cursors were opened with
** wrFlag==0 then this routine returns SQLITE_LOCKED.  If all

*/
static int checkReadLocks(BtCursor *pCur){
  BtCursor *p;
  assert( pCur->wrFlag );
  for(p=pCur->pShared; p!=pCur; p=p->pShared){
    assert( p );
    assert( p->pgnoRoot==pCur->pgnoRoot );
    assert( p->pPage->pgno==sqlitepager_pagenumber(p->pPage->aData);
    if( p->wrFlag==0 ) return SQLITE_LOCKED;
    if( p->pPage->pgno!=p->pgnoRoot ){
      moveToRoot(p);
    }
  }
  return SQLITE_OK;
}

/*
** Insert a new record into the BTree.  The key is given by (pKey,nKey)
** and the data is given by (pData,nData).  The cursor is used only to
** define what table the record should be inserted into.  The cursor
** is left pointing at a random location.
**
** For an INTKEY table, only the nKey value of the key is used.  pKey is
** ignored.  For a ZERODATA table, the pData and nData are both ignored.
*/
int sqlite3BtreeInsert(
  BtCursor *pCur,                /* Insert data into the table of this cursor */

  }
  if( checkReadLocks(pCur) ){
    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
  }
  rc = sqlite3BtreeMoveto(pCur, pKey, nKey, &loc);
  if( rc ) return rc;
  pPage = pCur->pPage;

  assert( pPage->isInit );
  rc = sqlitepager_write(pPage->aData);
  if( rc ) return rc;
  rc = fillInCell(pPage, &newCell, pKey, nKey, pData, nData, &szNew);
  if( rc ) return rc;
  assert( szNew==cellSize(pPage, newCell) );
  if( loc==0 ){
    int szOld
    assert( pCur->idx>=0 && pCur->idx<pPage->nPage );

  }
  if( !pCur->wrFlag ){
    return SQLITE_PERM;   /* Did not open this cursor for writing */
  }
  if( checkReadLocks(pCur) ){
    return SQLITE_LOCKED; /* The table pCur points to has a read lock */
  }
  rc = sqlitepager_write(pPage->aData);
  if( rc ) return rc;
  pCell = pPage->aCell[pCur->idx];
  if( !pPage->leaf ){
    pgnoChild = get4byte(&pCell[2]);
  }
  clearCell(pPage, pCell);
  if( !pPage->leaf ){

    int notUsed;
    getTempCursor(pCur, &leafCur);
    rc = sqlite3BtreeNext(&leafCur, &notUsed);
    if( rc!=SQLITE_OK ){
      if( rc!=SQLITE_NOMEM ) rc = SQLITE_CORRUPT;
      return rc;
    }
    rc = sqlitepager_write(leafCur.pPage->aData);
    if( rc ) return rc;
    dropCell(pPage, pCur->idx, cellSize(pPage, pCell));
    pNext = leafCur.pPage->aCell[leafCur.idx];
    szNext = cellSize(leafCur.pPage, pNext);
    insertCell(pPage, pCur->idx, &pNext[-4], szNext+4);
    put4byte(&pNext[-2], pgnoChild);
    rc = balance(pPage);

  if( pBt->readOnly ){
    return SQLITE_READONLY;
  }
  rc = allocatePage(pBt, &pRoot, &pgnoRoot, 0);
  if( rc ) return rc;
  assert( sqlitepager_iswriteable(pRoot->aData) );
  zeroPage(pBt, pRoot);
  sqlitepager_unref(pRoot->aData);
  *piTable = (int)pgnoRoot;
  return SQLITE_OK;
}

/*
** Erase the given database page and all its children.  Return
** the page to the freelist.

    while( idx>0 && idx<SQLITE_USABLE_SIZE-MIN_CELL_SIZE ){
      unsigned char *pCell = &pPage->aData[idx];
      fileBtreePageDump(pBt, get4byte(&pPage->aData[idx+2]), 1);
      idx = get2byte(&pPage->aData[idx]);
    }
    fileBtreePageDump(pBt, get4byte(&pPage->aData[hdrOffset+6]), 1);
  }
  sqlitepager_unref(pPage->aData);
  return SQLITE_OK;
}
#endif

#ifdef SQLITE_TEST
/*
** Fill aResult[] with information about the entry and page that the

** This routine is used for testing and debugging only.
*/
static int fileBtreeCursorDump(BtCursor *pCur, int *aResult){
  int cnt, idx;
  MemPage *pPage = pCur->pPage;
  Btree *pBt = pCur->pBt;
  assert( pPage->isInit );
  aResult[0] = sqlitepager_pagenumber(pPage->aData);
  assert( aResult[0]==pPage->pgno );
  aResult[1] = pCur->idx;
  aResult[2] = pPage->nCell;
  if( pCur->idx>=0 && pCur->idx<pPage->nCell ){
    aResult[3] = cellSize(pPage, pPage->aCell[pCur->idx]);
    aResult[6] = pPage->leaf ? 0 : get4byte(&pPage->aCell[pCur->idx][2]);
  }else{
    aResult[3] = 0;

    sprintf(zMsg, "unable to get the page. error code=%d", rc);
    checkAppendMsg(pCheck, zContext, zMsg);
    return 0;
  }
  if( (rc = initPage(pPage, pParent))!=0 ){
    sprintf(zMsg, "initPage() returns error code %d", rc);
    checkAppendMsg(pCheck, zContext, zMsg);
    releasePage(pPage);
    return 0;
  }

#if 0

  /* Check out all the cells.
  */