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Omit the check for cell-pointer consistency in sqlite3BtreeInitPage()

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for a 2.5% performance gain. (CVS 5433)

FossilOrigin-Name: b88087e69dffb743c5b552703e14a030349cf65b
This commit is contained in:
drh
2008-07-18 02:44:17 +00:00
parent 79df1f4a37
commit 1688c86f5a
4 changed files with 35 additions and 21 deletions
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37
src/btree.c
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@@ -9,7 +9,7 @@
** May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.485 2008/07/18 00:57:33 drh Exp $
** $Id: btree.c,v 1.486 2008/07/18 02:44:18 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
@@ -516,8 +516,8 @@ static int ptrmapGet(BtShared *pBt, Pgno key, u8 *pEType, Pgno *pPgno){
**
** 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)]))
#define findCell(P,I) \
((P)->aData + ((P)->maskPage & get2byte(&(P)->aData[(P)->cellOffset+2*(I)])))
/*
** This a more complex version of findCell() that works for
@@ -929,9 +929,6 @@ int sqlite3BtreeInitPage(
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 */
u8 *pOff; /* Iterator used to check all cell offsets are in range */
u8 *pEnd; /* Pointer to end of cell offset array */
u8 mask; /* Mask of bits that must be zero in MSB of cell offsets */
pBt = pPage->pBt;
assert( pBt!=0 );
@@ -952,6 +949,8 @@ int sqlite3BtreeInitPage(
hdr = pPage->hdrOffset;
data = pPage->aData;
if( decodeFlags(pPage, data[hdr]) ) return SQLITE_CORRUPT_BKPT;
assert( pBt->pageSize>=512 && pBt->pageSize<=32768 );
pPage->maskPage = pBt->pageSize - 1;
pPage->nOverflow = 0;
pPage->idxShift = 0;
usableSize = pBt->usableSize;
@@ -991,13 +990,25 @@ int sqlite3BtreeInitPage(
return SQLITE_CORRUPT_BKPT;
}
/* Check that all the offsets in the cell offset array are within range. */
mask = ~(((u8)(pBt->pageSize>>8))-1);
pEnd = &data[cellOffset + pPage->nCell*2];
for(pOff=&data[cellOffset]; pOff!=pEnd && !((*pOff)&mask); pOff+=2);
if( pOff!=pEnd ){
return SQLITE_CORRUPT_BKPT;
#if 0
/* Check that all the offsets in the cell offset array are within range.
**
** Omitting this consistency check and using the pPage->maskPage mask
** to prevent overrunning the page buffer in findCell() results in a
** 2.5% performance gain.
*/
{
u8 *pOff; /* Iterator used to check all cell offsets are in range */
u8 *pEnd; /* Pointer to end of cell offset array */
u8 mask; /* Mask of bits that must be zero in MSB of cell offsets */
mask = ~(((u8)(pBt->pageSize>>8))-1);
pEnd = &data[cellOffset + pPage->nCell*2];
for(pOff=&data[cellOffset]; pOff!=pEnd && !((*pOff)&mask); pOff+=2);
if( pOff!=pEnd ){
return SQLITE_CORRUPT_BKPT;
}
}
#endif
pPage->isInit = 1;
return SQLITE_OK;
@@ -1029,6 +1040,8 @@ static void zeroPage(MemPage *pPage, int flags){
pPage->hdrOffset = hdr;
pPage->cellOffset = first;
pPage->nOverflow = 0;
assert( pBt->pageSize>=512 && pBt->pageSize<=32768 );
pPage->maskPage = pBt->pageSize - 1;
pPage->idxShift = 0;
pPage->nCell = 0;
pPage->isInit = 1;