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Small performance increase and size decrease in the btreeInitPage() routine.

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FossilOrigin-Name: 6f415833e0554706dcf04f68ecba4ca2e54c08f3bbf6a1dba182bb132c912a2e
This commit is contained in:
drh
2017-05-25 21:35:56 +00:00
parent 137c46f8b6
commit 14e845a9d4
3 changed files with 117 additions and 120 deletions
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223
src/btree.c
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@@ -1781,6 +1781,16 @@ static int decodeFlags(MemPage *pPage, int flagByte){
** we failed to detect any corruption.
*/
static int btreeInitPage(MemPage *pPage){
int pc; /* Address of a freeblock within pPage->aData[] */
u8 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 */
u16 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 */
int iCellFirst; /* First allowable cell or freeblock offset */
int iCellLast; /* Last possible cell or freeblock offset */
assert( pPage->pBt!=0 );
assert( pPage->pBt->db!=0 );
@@ -1788,127 +1798,114 @@ static int btreeInitPage(MemPage *pPage){
assert( pPage->pgno==sqlite3PagerPagenumber(pPage->pDbPage) );
assert( pPage == sqlite3PagerGetExtra(pPage->pDbPage) );
assert( pPage->aData == sqlite3PagerGetData(pPage->pDbPage) );
assert( pPage->isInit==0 );
if( !pPage->isInit ){
int pc; /* Address of a freeblock within pPage->aData[] */
u8 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 */
u16 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 */
int iCellFirst; /* First allowable cell or freeblock offset */
int iCellLast; /* Last possible cell or freeblock offset */
pBt = pPage->pBt;
hdr = pPage->hdrOffset;
data = pPage->aData;
/* EVIDENCE-OF: R-28594-02890 The one-byte flag at offset 0 indicating
** the b-tree page type. */
if( decodeFlags(pPage, data[hdr]) ) return SQLITE_CORRUPT_BKPT;
assert( pBt->pageSize>=512 && pBt->pageSize<=65536 );
pPage->maskPage = (u16)(pBt->pageSize - 1);
pPage->nOverflow = 0;
usableSize = pBt->usableSize;
pPage->cellOffset = cellOffset = hdr + 8 + pPage->childPtrSize;
pPage->aDataEnd = &data[usableSize];
pPage->aCellIdx = &data[cellOffset];
pPage->aDataOfst = &data[pPage->childPtrSize];
/* EVIDENCE-OF: R-58015-48175 The two-byte integer at offset 5 designates
** the start of the cell content area. A zero value for this integer is
** interpreted as 65536. */
top = get2byteNotZero(&data[hdr+5]);
/* EVIDENCE-OF: R-37002-32774 The two-byte integer at offset 3 gives the
** number of cells on the page. */
pPage->nCell = get2byte(&data[hdr+3]);
if( pPage->nCell>MX_CELL(pBt) ){
/* To many cells for a single page. The page must be corrupt */
return SQLITE_CORRUPT_BKPT;
}
testcase( pPage->nCell==MX_CELL(pBt) );
/* EVIDENCE-OF: R-24089-57979 If a page contains no cells (which is only
** possible for a root page of a table that contains no rows) then the
** offset to the cell content area will equal the page size minus the
** bytes of reserved space. */
assert( pPage->nCell>0 || top==usableSize || CORRUPT_DB );
pBt = pPage->pBt;
/* A malformed database page might cause us to read past the end
** of page when parsing a cell.
**
** The following block of code checks early to see if a cell extends
** past the end of a page boundary and causes SQLITE_CORRUPT to be
** returned if it does.
*/
iCellFirst = cellOffset + 2*pPage->nCell;
iCellLast = usableSize - 4;
if( pBt->db->flags & SQLITE_CellSizeCk ){
int i; /* Index into the cell pointer array */
int sz; /* Size of a cell */
hdr = pPage->hdrOffset;
data = pPage->aData;
/* EVIDENCE-OF: R-28594-02890 The one-byte flag at offset 0 indicating
** the b-tree page type. */
if( decodeFlags(pPage, data[hdr]) ) return SQLITE_CORRUPT_BKPT;
assert( pBt->pageSize>=512 && pBt->pageSize<=65536 );
pPage->maskPage = (u16)(pBt->pageSize - 1);
pPage->nOverflow = 0;
usableSize = pBt->usableSize;
pPage->cellOffset = cellOffset = hdr + 8 + pPage->childPtrSize;
pPage->aDataEnd = &data[usableSize];
pPage->aCellIdx = &data[cellOffset];
pPage->aDataOfst = &data[pPage->childPtrSize];
/* EVIDENCE-OF: R-58015-48175 The two-byte integer at offset 5 designates
** the start of the cell content area. A zero value for this integer is
** interpreted as 65536. */
top = get2byteNotZero(&data[hdr+5]);
/* EVIDENCE-OF: R-37002-32774 The two-byte integer at offset 3 gives the
** number of cells on the page. */
pPage->nCell = get2byte(&data[hdr+3]);
if( pPage->nCell>MX_CELL(pBt) ){
/* To many cells for a single page. The page must be corrupt */
return SQLITE_CORRUPT_BKPT;
}
testcase( pPage->nCell==MX_CELL(pBt) );
/* EVIDENCE-OF: R-24089-57979 If a page contains no cells (which is only
** possible for a root page of a table that contains no rows) then the
** offset to the cell content area will equal the page size minus the
** bytes of reserved space. */
assert( pPage->nCell>0 || top==usableSize || CORRUPT_DB );
/* A malformed database page might cause us to read past the end
** of page when parsing a cell.
**
** The following block of code checks early to see if a cell extends
** past the end of a page boundary and causes SQLITE_CORRUPT to be
** returned if it does.
*/
iCellFirst = cellOffset + 2*pPage->nCell;
iCellLast = usableSize - 4;
if( pBt->db->flags & SQLITE_CellSizeCk ){
int i; /* Index into the cell pointer array */
int sz; /* Size of a cell */
if( !pPage->leaf ) iCellLast--;
for(i=0; i<pPage->nCell; i++){
pc = get2byteAligned(&data[cellOffset+i*2]);
testcase( pc==iCellFirst );
testcase( pc==iCellLast );
if( pc<iCellFirst || pc>iCellLast ){
return SQLITE_CORRUPT_BKPT;
}
sz = pPage->xCellSize(pPage, &data[pc]);
testcase( pc+sz==usableSize );
if( pc+sz>usableSize ){
return SQLITE_CORRUPT_BKPT;
}
if( !pPage->leaf ) iCellLast--;
for(i=0; i<pPage->nCell; i++){
pc = get2byteAligned(&data[cellOffset+i*2]);
testcase( pc==iCellFirst );
testcase( pc==iCellLast );
if( pc<iCellFirst || pc>iCellLast ){
return SQLITE_CORRUPT_BKPT;
}
if( !pPage->leaf ) iCellLast++;
}
/* Compute the total free space on the page
** EVIDENCE-OF: R-23588-34450 The two-byte integer at offset 1 gives the
** start of the first freeblock on the page, or is zero if there are no
** freeblocks. */
pc = get2byte(&data[hdr+1]);
nFree = data[hdr+7] + top; /* Init nFree to non-freeblock free space */
if( pc>0 ){
u32 next, size;
if( pc<iCellFirst ){
/* EVIDENCE-OF: R-55530-52930 In a well-formed b-tree page, there will
** always be at least one cell before the first freeblock.
*/
return SQLITE_CORRUPT_BKPT;
}
while( 1 ){
if( pc>iCellLast ){
return SQLITE_CORRUPT_BKPT; /* Freeblock off the end of the page */
}
next = get2byte(&data[pc]);
size = get2byte(&data[pc+2]);
nFree = nFree + size;
if( next<=pc+size+3 ) break;
pc = next;
}
if( next>0 ){
return SQLITE_CORRUPT_BKPT; /* Freeblock not in ascending order */
}
if( pc+size>(unsigned int)usableSize ){
return SQLITE_CORRUPT_BKPT; /* Last freeblock extends past page end */
sz = pPage->xCellSize(pPage, &data[pc]);
testcase( pc+sz==usableSize );
if( pc+sz>usableSize ){
return SQLITE_CORRUPT_BKPT;
}
}
if( !pPage->leaf ) iCellLast++;
}
/* At this point, nFree contains the sum of the offset to the start
** of the cell-content area plus the number of free bytes within
** the cell-content area. If this is greater than the usable-size
** of the page, then the page must be corrupted. This check also
** serves to verify that the offset to the start of the cell-content
** area, according to the page header, lies within the page.
*/
if( nFree>usableSize ){
/* Compute the total free space on the page
** EVIDENCE-OF: R-23588-34450 The two-byte integer at offset 1 gives the
** start of the first freeblock on the page, or is zero if there are no
** freeblocks. */
pc = get2byte(&data[hdr+1]);
nFree = data[hdr+7] + top; /* Init nFree to non-freeblock free space */
if( pc>0 ){
u32 next, size;
if( pc<iCellFirst ){
/* EVIDENCE-OF: R-55530-52930 In a well-formed b-tree page, there will
** always be at least one cell before the first freeblock.
*/
return SQLITE_CORRUPT_BKPT;
}
pPage->nFree = (u16)(nFree - iCellFirst);
pPage->isInit = 1;
while( 1 ){
if( pc>iCellLast ){
return SQLITE_CORRUPT_BKPT; /* Freeblock off the end of the page */
}
next = get2byte(&data[pc]);
size = get2byte(&data[pc+2]);
nFree = nFree + size;
if( next<=pc+size+3 ) break;
pc = next;
}
if( next>0 ){
return SQLITE_CORRUPT_BKPT; /* Freeblock not in ascending order */
}
if( pc+size>(unsigned int)usableSize ){
return SQLITE_CORRUPT_BKPT; /* Last freeblock extends past page end */
}
}
/* At this point, nFree contains the sum of the offset to the start
** of the cell-content area plus the number of free bytes within
** the cell-content area. If this is greater than the usable-size
** of the page, then the page must be corrupted. This check also
** serves to verify that the offset to the start of the cell-content
** area, according to the page header, lies within the page.
*/
if( nFree>usableSize ){
return SQLITE_CORRUPT_BKPT;
}
pPage->nFree = (u16)(nFree - iCellFirst);
pPage->isInit = 1;
return SQLITE_OK;
}
@@ -3360,7 +3357,7 @@ static int setChildPtrmaps(MemPage *pPage){
Pgno pgno = pPage->pgno;
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
rc = btreeInitPage(pPage);
rc = pPage->isInit ? SQLITE_OK : btreeInitPage(pPage);
if( rc!=SQLITE_OK ) return rc;
nCell = pPage->nCell;
@@ -3411,7 +3408,7 @@ static int modifyPagePointer(MemPage *pPage, Pgno iFrom, Pgno iTo, u8 eType){
int nCell;
int rc;
rc = btreeInitPage(pPage);
rc = pPage->isInit ? SQLITE_OK : btreeInitPage(pPage);
if( rc ) return rc;
nCell = pPage->nCell;