btree.c

来自「sqlite-3.4.1,嵌入式数据库.是一个功能强大的开源数据库,给学习和研发」· C语言 代码 · 共 2,088 行 · 第 1/5 页

**
** This routine works only for pages that do not contain overflow cells.
*/
#define findCell(pPage, iCell) \
  ((pPage)->aData + get2byte(&(pPage)->aData[(pPage)->cellOffset+2*(iCell)]))
u8 *sqlite3BtreeFindCell(MemPage *pPage, int iCell){
  assert( iCell>=0 );
  assert( iCell<get2byte(&pPage->aData[pPage->hdrOffset+3]) );
  return findCell(pPage, iCell);
}

/*
** This a more complex version of sqlite3BtreeFindCell() that works for
** pages that do contain overflow cells.  See insert
*/
static u8 *findOverflowCell(MemPage *pPage, int iCell){
  int i;
  for(i=pPage->nOverflow-1; i>=0; i--){
    int k;
    struct _OvflCell *pOvfl;
    pOvfl = &pPage->aOvfl[i];
    k = pOvfl->idx;
    if( k<=iCell ){
      if( k==iCell ){
        return pOvfl->pCell;
      }
      iCell--;
    }
  }
  return findCell(pPage, iCell);
}

/*
** Parse a cell content block and fill in the CellInfo structure.  There
** are two versions of this function.  sqlite3BtreeParseCell() takes a 
** cell index as the second argument and sqlite3BtreeParseCellPtr() 
** takes a pointer to the body of the cell as its second argument.
**
** Within this file, the parseCell() macro can be called instead of
** sqlite3BtreeParseCellPtr(). Using some compilers, this will be faster.
*/
void sqlite3BtreeParseCellPtr(
  MemPage *pPage,         /* Page containing the cell */
  u8 *pCell,              /* Pointer to the cell text. */
  CellInfo *pInfo         /* Fill in this structure */
){
  int n;                  /* Number bytes in cell content header */
  u32 nPayload;           /* Number of bytes of cell payload */

  pInfo->pCell = pCell;
  assert( pPage->leaf==0 || pPage->leaf==1 );
  n = pPage->childPtrSize;
  assert( n==4-4*pPage->leaf );
  if( pPage->hasData ){
    n += getVarint32(&pCell[n], &nPayload);
  }else{
    nPayload = 0;
  }
  pInfo->nData = nPayload;
  if( pPage->intKey ){
    n += getVarint(&pCell[n], (u64 *)&pInfo->nKey);
  }else{
    u32 x;
    n += getVarint32(&pCell[n], &x);
    pInfo->nKey = x;
    nPayload += x;
  }
  pInfo->nPayload = nPayload;
  pInfo->nHeader = n;
  if( nPayload<=pPage->maxLocal ){
    /* This is the (easy) common case where the entire payload fits
    ** on the local page.  No overflow is required.
    */
    int nSize;          /* Total size of cell content in bytes */
    pInfo->nLocal = nPayload;
    pInfo->iOverflow = 0;
    nSize = nPayload + n;
    if( nSize<4 ){
      nSize = 4;        /* Minimum cell size is 4 */
    }
    pInfo->nSize = nSize;
  }else{
    /* If the payload will not fit completely on the local page, we have
    ** to decide how much to store locally and how much to spill onto
    ** overflow pages.  The strategy is to minimize the amount of unused
    ** space on overflow pages while keeping the amount of local storage
    ** in between minLocal and maxLocal.
    **
    ** Warning:  changing the way overflow payload is distributed in any
    ** way will result in an incompatible file format.
    */
    int minLocal;  /* Minimum amount of payload held locally */
    int maxLocal;  /* Maximum amount of payload held locally */
    int surplus;   /* Overflow payload available for local storage */

    minLocal = pPage->minLocal;
    maxLocal = pPage->maxLocal;
    surplus = minLocal + (nPayload - minLocal)%(pPage->pBt->usableSize - 4);
    if( surplus <= maxLocal ){
      pInfo->nLocal = surplus;
    }else{
      pInfo->nLocal = minLocal;
    }
    pInfo->iOverflow = pInfo->nLocal + n;
    pInfo->nSize = pInfo->iOverflow + 4;
  }
}
#define parseCell(pPage, iCell, pInfo) \
  sqlite3BtreeParseCellPtr((pPage), findCell((pPage), (iCell)), (pInfo))
void sqlite3BtreeParseCell(
  MemPage *pPage,         /* Page containing the cell */
  int iCell,              /* The cell index.  First cell is 0 */
  CellInfo *pInfo         /* Fill in this structure */
){
  parseCell(pPage, iCell, pInfo);
}

/*
** Compute the total number of bytes that a Cell needs in the cell
** data area of the btree-page.  The return number includes the cell
** data header and the local payload, but not any overflow page or
** the space used by the cell pointer.
*/
#ifndef NDEBUG
static int cellSize(MemPage *pPage, int iCell){
  CellInfo info;
  sqlite3BtreeParseCell(pPage, iCell, &info);
  return info.nSize;
}
#endif
static int cellSizePtr(MemPage *pPage, u8 *pCell){
  CellInfo info;
  sqlite3BtreeParseCellPtr(pPage, pCell, &info);
  return info.nSize;
}

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** If the cell pCell, part of page pPage contains a pointer
** to an overflow page, insert an entry into the pointer-map
** for the overflow page.
*/
static int ptrmapPutOvflPtr(MemPage *pPage, u8 *pCell){
  if( pCell ){
    CellInfo info;
    sqlite3BtreeParseCellPtr(pPage, pCell, &info);
    assert( (info.nData+(pPage->intKey?0:info.nKey))==info.nPayload );
    if( (info.nData+(pPage->intKey?0:info.nKey))>info.nLocal ){
      Pgno ovfl = get4byte(&pCell[info.iOverflow]);
      return ptrmapPut(pPage->pBt, ovfl, PTRMAP_OVERFLOW1, pPage->pgno);
    }
  }
  return SQLITE_OK;
}
/*
** If the cell with index iCell on page pPage contains a pointer
** to an overflow page, insert an entry into the pointer-map
** for the overflow page.
*/
static int ptrmapPutOvfl(MemPage *pPage, int iCell){
  u8 *pCell;
  pCell = findOverflowCell(pPage, iCell);
  return ptrmapPutOvflPtr(pPage, pCell);
}
#endif


/*
** Defragment the page given.  All Cells are moved to the
** end of the page and all free space is collected into one
** big FreeBlk that occurs in between the header and cell
** pointer array and the cell content area.
*/
static int defragmentPage(MemPage *pPage){
  int i;                     /* Loop counter */
  int pc;                    /* Address of a i-th cell */
  int addr;                  /* Offset of first byte after cell pointer array */
  int hdr;                   /* Offset to the page header */
  int size;                  /* Size of a cell */
  int usableSize;            /* Number of usable bytes on a page */
  int cellOffset;            /* Offset to the cell pointer array */
  int brk;                   /* Offset to the cell content area */
  int nCell;                 /* Number of cells on the page */
  unsigned char *data;       /* The page data */
  unsigned char *temp;       /* Temp area for cell content */

  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( pPage->pBt!=0 );
  assert( pPage->pBt->usableSize <= SQLITE_MAX_PAGE_SIZE );
  assert( pPage->nOverflow==0 );
  temp = sqliteMalloc( pPage->pBt->pageSize );
  if( temp==0 ) return SQLITE_NOMEM;
  data = pPage->aData;
  hdr = pPage->hdrOffset;
  cellOffset = pPage->cellOffset;
  nCell = pPage->nCell;
  assert( nCell==get2byte(&data[hdr+3]) );
  usableSize = pPage->pBt->usableSize;
  brk = get2byte(&data[hdr+5]);
  memcpy(&temp[brk], &data[brk], usableSize - brk);
  brk = usableSize;
  for(i=0; i<nCell; i++){
    u8 *pAddr;     /* The i-th cell pointer */
    pAddr = &data[cellOffset + i*2];
    pc = get2byte(pAddr);
    assert( pc<pPage->pBt->usableSize );
    size = cellSizePtr(pPage, &temp[pc]);
    brk -= size;
    memcpy(&data[brk], &temp[pc], size);
    put2byte(pAddr, brk);
  }
  assert( brk>=cellOffset+2*nCell );
  put2byte(&data[hdr+5], brk);
  data[hdr+1] = 0;
  data[hdr+2] = 0;
  data[hdr+7] = 0;
  addr = cellOffset+2*nCell;
  memset(&data[addr], 0, brk-addr);
  sqliteFree(temp);
  return SQLITE_OK;
}

/*
** Allocate nByte bytes of space on a page.
**
** Return the index into pPage->aData[] of the first byte of
** the new allocation. Or return 0 if there is not enough free
** space on the page to satisfy the allocation request.
**
** If the page contains nBytes of free space but does not contain
** nBytes of contiguous free space, then this routine automatically
** calls defragementPage() to consolidate all free space before 
** allocating the new chunk.
*/
static int allocateSpace(MemPage *pPage, int nByte){
  int addr, pc, hdr;
  int size;
  int nFrag;
  int top;
  int nCell;
  int cellOffset;
  unsigned char *data;
  
  data = pPage->aData;
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( pPage->pBt );
  if( nByte<4 ) nByte = 4;
  if( pPage->nFree<nByte || pPage->nOverflow>0 ) return 0;
  pPage->nFree -= nByte;
  hdr = pPage->hdrOffset;

  nFrag = data[hdr+7];
  if( nFrag<60 ){
    /* Search the freelist looking for a slot big enough to satisfy the
    ** space request. */
    addr = hdr+1;
    while( (pc = get2byte(&data[addr]))>0 ){
      size = get2byte(&data[pc+2]);
      if( size>=nByte ){
        if( size<nByte+4 ){
          memcpy(&data[addr], &data[pc], 2);
          data[hdr+7] = nFrag + size - nByte;
          return pc;
        }else{
          put2byte(&data[pc+2], size-nByte);
          return pc + size - nByte;
        }
      }
      addr = pc;
    }
  }

  /* Allocate memory from the gap in between the cell pointer array
  ** and the cell content area.
  */
  top = get2byte(&data[hdr+5]);
  nCell = get2byte(&data[hdr+3]);
  cellOffset = pPage->cellOffset;
  if( nFrag>=60 || cellOffset + 2*nCell > top - nByte ){
    if( defragmentPage(pPage) ) return 0;
    top = get2byte(&data[hdr+5]);
  }
  top -= nByte;
  assert( cellOffset + 2*nCell <= top );
  put2byte(&data[hdr+5], top);
  return top;
}

/*
** Return a section of the pPage->aData to the freelist.
** The first byte of the new free block is pPage->aDisk[start]
** and the size of the block is "size" bytes.
**
** Most of the effort here is involved in coalesing adjacent
** free blocks into a single big free block.
*/
static void freeSpace(MemPage *pPage, int start, int size){
  int addr, pbegin, hdr;
  unsigned char *data = pPage->aData;

  assert( pPage->pBt!=0 );
  assert( sqlite3PagerIswriteable(pPage->pDbPage) );
  assert( start>=pPage->hdrOffset+6+(pPage->leaf?0:4) );
  assert( (start + size)<=pPage->pBt->usableSize );
  if( size<4 ) size = 4;

#ifdef SQLITE_SECURE_DELETE
  /* Overwrite deleted information with zeros when the SECURE_DELETE 
  ** option is enabled at compile-time */
  memset(&data[start], 0, size);
#endif

  /* Add the space back into the linked list of freeblocks */
  hdr = pPage->hdrOffset;
  addr = hdr + 1;
  while( (pbegin = get2byte(&data[addr]))<start && pbegin>0 ){
    assert( pbegin<=pPage->pBt->usableSize-4 );
    assert( pbegin>addr );
    addr = pbegin;
  }
  assert( pbegin<=pPage->pBt->usableSize-4 );
  assert( pbegin>addr || pbegin==0 );
  put2byte(&data[addr], start);
  put2byte(&data[start], pbegin);
  put2byte(&data[start+2], size);
  pPage->nFree += size;

  /* Coalesce adjacent free blocks */
  addr = pPage->hdrOffset + 1;
  while( (pbegin = get2byte(&data[addr]))>0 ){
    int pnext, psize;
    assert( pbegin>addr );
    assert( pbegin<=pPage->pBt->usableSize-4 );
    pnext = get2byte(&data[pbegin]);
    psize = get2byte(&data[pbegin+2]);
    if( pbegin + psize + 3 >= pnext && pnext>0 ){
      int frag = pnext - (pbegin+psize);
      assert( frag<=data[pPage->hdrOffset+7] );
      data[pPage->hdrOffset+7] -= frag;
      put2byte(&data[pbegin], get2byte(&data[pnext]));
      put2byte(&data[pbegin+2], pnext+get2byte(&data[pnext+2])-pbegin);
    }else{
      addr = pbegin;
    }
  }

  /* If the cell content area begins with a freeblock, remove it. */
  if( data[hdr+1]==data[hdr+5] && data[hdr+2]==data[hdr+6] ){
    int top;
    pbegin = get2byte(&data[hdr+1]);
    memcpy(&data[hdr+1], &data[pbegin], 2);
    top = get2byte(&data[hdr+5]);
    put2byte(&data[hdr+5], top + get2byte(&data[pbegin+2]));
  }
}

/*
** Decode the flags byte (the first byte of the header) for a page
** and initialize fields of the MemPage structure accordingly.
*/
static void decodeFlags(MemPage *pPage, int flagByte){
  BtShared *pBt;     /* A copy of pPage->pBt */

  assert( pPage->hdrOffset==(pPage->pgno==1 ? 100 : 0) );
  pPage->intKey = (flagByte & (PTF_INTKEY|PTF_LEAFDATA))!=0;
  pPage->zeroData = (flagByte & PTF_ZERODATA)!=0;
  pPage->leaf = (flagByte & PTF_LEAF)!=0;
  pPage->childPtrSize = 4*(pPage->leaf==0);
  pBt = pPage->pBt;
  if( flagByte & PTF_LEAFDATA ){
    pPage->leafData = 1;
    pPage->maxLocal = pBt->maxLeaf;
    pPage->minLocal = pBt->minLeaf;
  }else{
    pPage->leafData = 0;
    pPage->maxLocal = pBt->maxLocal;
    pPage->minLocal = pBt->minLocal;
  }
  pPage->hasData = !(pPage->zeroData || (!pPage->leaf && pPage->leafData));
}

/*
** Initialize the auxiliary information for a disk block.
**
** The pParent parameter must be a pointer to the MemPage which
** is the parent of the page being initialized.  The root of a
** BTree has no parent and so for that page, pParent==NULL.
**
** Return SQLITE_OK on success.  If we see that the page does
** not contain a well-formed database page, then return 
** SQLITE_CORRUPT.  Note that a return of SQLITE_OK does not
** guarantee that the page is well-formed.  It only shows that
** we failed to detect any corruption.
*/
int sqlite3BtreeInitPage(
  MemPage *pPage,        /* The page to be initialized */
  MemPage *pParent       /* The parent.  Might be NULL */
){
  int pc;            /* Address of a freeblock within pPage->aData[] */
  int hdr;           /* Offset to beginning of page header */
  u8 *data;          /* Equal to pPage->aData */
  BtShared *pBt;        /* The main btree structure */
  int usableSize;    /* Amount of usable space on each page */
  int cellOffset;    /* Offset from start of page to first cell pointer */
  int nFree;         /* Number of unused bytes on the page */
  int top;           /* First byte of the cell content area */

  pBt = pPage->pBt;
  assert( pBt!=0 );
  assert( pParent==0 || pParent->pBt==pBt );
  assert( pPage->pgno==sqlite3PagerPagenumber(pPage->pDbPage) );
  assert( pPage->aData == &((unsigned char*)pPage)[-pBt->pageSize] );
  if( pPage->pParent!=pParent && (pPage->pParent!=0 || pPage->isInit) ){
    /* The parent page should never change unless the file is corrupt */
    return SQLITE_CORRUPT_BKPT;
  }
  if( pPage->isInit ) return SQLITE_OK;
  if( pPage->pParent==0 && pParent!=0 ){