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Reimplement the freeSpace() routine in btree.c so that it runs faster.

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FossilOrigin-Name: fe4fd014b42b7b158ca968f1535b5636c67769f6
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drh
2014-08-20 17:56:27 +00:00
parent 7fb91646b5
commit 5f5c753efb
3 changed files with 70 additions and 69 deletions
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125
src/btree.c
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@@ -1293,92 +1293,93 @@ defragment_page:
** The first byte of the new free block is pPage->aData[iStart]
** and the size of the block is iSize bytes.
**
** Most of the effort here is involved in coalesing adjacent
** free blocks into a single big free block.
** Adjacent freeblocks are coalesced.
**
** Note that even though the freeblock list was checked by btreeInitPage(),
** that routine will not detect overlap between cells or freeblocks. Nor
** does it detect cells or freeblocks that encrouch into the reserved bytes
** at the end of the page. So do additional corruption checks inside this
** routine and return SQLITE_CORRUPT if any problems are found.
*/
static int freeSpace(MemPage *pPage, int iStart, int iSize){
int iPtr; /* Address of pointer to next freeblock */
int iFreeBlk; /* Address of the next freeblock */
int hdr; /* Page header size. 0 or 100 */
int iLast; /* Largest possible freeblock offset */
static int freeSpace(MemPage *pPage, u16 iStart, u16 iSize){
u16 iPtr; /* Address of pointer to next freeblock */
u16 iFreeBlk; /* Address of the next freeblock */
u8 hdr; /* Page header size. 0 or 100 */
u8 nFrag = 0; /* Reduction in fragmentation */
u16 iOrigSize = iSize; /* Original value of iSize */
u32 iLast = pPage->pBt->usableSize-4; /* Largest possible freeblock offset */
u32 iEnd = iStart + iSize; /* First byte past the iStart buffer */
unsigned char *data = pPage->aData; /* Page content */
assert( pPage->pBt!=0 );
assert( sqlite3PagerIswriteable(pPage->pDbPage) );
assert( iStart>=pPage->hdrOffset+6+pPage->childPtrSize );
assert( (iStart + iSize) <= (int)pPage->pBt->usableSize );
assert( iEnd <= pPage->pBt->usableSize );
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
assert( iSize>=4 ); /* Minimum cell size is 4 */
assert( iStart<=iLast );
/* Overwrite deleted information with zeros when the secure_delete
** option is enabled */
if( pPage->pBt->btsFlags & BTS_SECURE_DELETE ){
/* Overwrite deleted information with zeros when the secure_delete
** option is enabled */
memset(&data[iStart], 0, iSize);
}
/* Add the space back into the linked list of freeblocks. Note that
** even though the freeblock list was checked by btreeInitPage(),
** btreeInitPage() did not detect overlapping cells or
** freeblocks that overlapped cells. Nor does it detect when the
** cell content area exceeds the value in the page header. If these
** situations arise, then subsequent insert operations might corrupt
** the freelist. So we do need to check for corruption while scanning
** the freelist.
/* The list of freeblocks must be in ascending order. Find the
** spot on the list where iStart should be inserted.
*/
hdr = pPage->hdrOffset;
iPtr = hdr + 1;
iLast = pPage->pBt->usableSize - 4;
assert( iStart<=iLast );
while( (iFreeBlk = get2byte(&data[iPtr]))<iStart && iFreeBlk>0 ){
if( iFreeBlk<iPtr+4 ){
return SQLITE_CORRUPT_BKPT;
}
while( (iFreeBlk = get2byte(&data[iPtr]))>0 && iFreeBlk<iStart ){
if( iFreeBlk<iPtr+4 ) return SQLITE_CORRUPT_BKPT;
iPtr = iFreeBlk;
}
if( iFreeBlk>iLast ){
return SQLITE_CORRUPT_BKPT;
}
if( iFreeBlk>iLast ) return SQLITE_CORRUPT_BKPT;
assert( iFreeBlk>iPtr || iFreeBlk==0 );
put2byte(&data[iPtr], iStart);
put2byte(&data[iStart], iFreeBlk);
put2byte(&data[iStart+2], iSize);
pPage->nFree = pPage->nFree + (u16)iSize;
/* Coalesce adjacent free blocks */
iPtr = hdr + 1;
while( (iFreeBlk = get2byte(&data[iPtr]))>0 ){
int iNextBlk; /* Next freeblock after iFreeBlk */
int szFreeBlk; /* Size of iFreeBlk */
assert( iFreeBlk>iPtr );
assert( iFreeBlk <= (int)pPage->pBt->usableSize-4 );
iNextBlk = get2byte(&data[iFreeBlk]);
szFreeBlk = get2byte(&data[iFreeBlk+2]);
if( iFreeBlk + szFreeBlk + 3 >= iNextBlk && iNextBlk>0 ){
int nFrag; /* Fragment bytes in between iFreeBlk and iNextBlk */
int x; /* Temp value */
nFrag = iNextBlk - (iFreeBlk+szFreeBlk);
if( (nFrag<0) || (nFrag>(int)data[hdr+7]) ){
return SQLITE_CORRUPT_BKPT;
}
data[hdr+7] -= (u8)nFrag;
x = get2byte(&data[iNextBlk]);
put2byte(&data[iFreeBlk], x);
x = iNextBlk + get2byte(&data[iNextBlk+2]) - iFreeBlk;
put2byte(&data[iFreeBlk+2], x);
}else{
iPtr = iFreeBlk;
/* At this point:
** iFreeBlk: First freeblock after iStart, or zero if none
** iPtr: The address of a pointer iFreeBlk
**
** Check to see if iFreeBlk should be coalesced onto the end of iStart.
*/
if( iFreeBlk && iEnd+3>=iFreeBlk ){
nFrag = iFreeBlk - iEnd;
if( iEnd>iFreeBlk ) return SQLITE_CORRUPT_BKPT;
iEnd = iFreeBlk + get2byte(&data[iFreeBlk+2]);
iSize = iEnd - iStart;
iFreeBlk = get2byte(&data[iFreeBlk]);
}
/* If iPtr is another freeblock (that is, if iPtr is not the freelist pointer
** in the page header) then check to see if iStart should be coalesced
** onto the end of iPtr.
*/
if( iPtr>hdr+1 ){
int iPtrEnd = iPtr + get2byte(&data[iPtr+2]);
if( iPtrEnd+3>=iStart ){
if( iPtrEnd>iStart ) return SQLITE_CORRUPT_BKPT;
nFrag += iStart - iPtrEnd;
iSize = iEnd - iPtr;
iStart = iPtr;
}
}
if( nFrag>data[hdr+7] ) return SQLITE_CORRUPT_BKPT;
/* 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;
iFreeBlk = get2byte(&data[hdr+1]);
memcpy(&data[hdr+1], &data[iFreeBlk], 2);
top = get2byte(&data[hdr+5]) + get2byte(&data[iFreeBlk+2]);
put2byte(&data[hdr+5], top);
data[hdr+7] -= nFrag;
if( iPtr==hdr+1 && iStart==get2byte(&data[hdr+5]) ){
/* The new freeblock is at the beginning of the cell content area,
** so just extend the cell content area rather than create another
** freelist entry */
put2byte(&data[hdr+1], iFreeBlk);
put2byte(&data[hdr+5], iEnd);
}else{
/* Insert the new freeblock into the freelist */
put2byte(&data[iPtr], iStart);
put2byte(&data[iStart], iFreeBlk);
put2byte(&data[iStart+2], iSize);
}
assert( sqlite3PagerIswriteable(pPage->pDbPage) );
pPage->nFree += iOrigSize;
return SQLITE_OK;
}