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Defer computing the MemPage.nFree value of an in-memory btree page

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until it is actually needed, since for many pages it is never needed.
This checkin works sufficiently to prove the concept, but still has issues
with exception handling.

FossilOrigin-Name: 1d43ee4000b71f5c6d49244dee96358c567f09ba3451b9d22895a796d3f61ad6
This commit is contained in:
drh
2019-02-09 21:06:40 +00:00
parent 2fa619a3a8
commit b0ea9432a1
4 changed files with 159 additions and 85 deletions
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221
src/btree.c
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@@ -1506,6 +1506,7 @@ static int defragmentPage(MemPage *pPage, int nMaxFrag){
data[hdr+7] = 0;
defragment_out:
assert( pPage->nFree>=0 );
if( data[hdr+7]+cbrk-iCellFirst!=pPage->nFree ){
return SQLITE_CORRUPT_PAGE(pPage);
}
@@ -1657,6 +1658,7 @@ static int allocateSpace(MemPage *pPage, int nByte, int *pIdx){
testcase( gap+2+nByte==top );
if( gap+2+nByte>top ){
assert( pPage->nCell>0 || CORRUPT_DB );
assert( pPage->nFree>=0 );
rc = defragmentPage(pPage, MIN(4, pPage->nFree - (2+nByte)));
if( rc ) return rc;
top = get2byteNotZero(&data[hdr+5]);
@@ -1846,21 +1848,14 @@ static int decodeFlags(MemPage *pPage, int flagByte){
}
/*
** Initialize the auxiliary information for a disk block.
**
** 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.
** Compute the amount of freespace on the page. In other words, fill
** in the pPage->nFree field.
*/
static int btreeInitPage(MemPage *pPage){
static int btreeComputeFreeSpace(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 */
@@ -1872,71 +1867,18 @@ 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 );
assert( pPage->isInit==1 );
assert( pPage->nFree<0 );
pBt = pPage->pBt;
usableSize = pPage->pBt->usableSize;
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_PAGE(pPage);
}
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_PAGE(pPage);
}
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;
iCellFirst = hdr + 8 + pPage->childPtrSize + 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_PAGE(pPage);
}
sz = pPage->xCellSize(pPage, &data[pc]);
testcase( pc+sz==usableSize );
if( pc+sz>usableSize ){
return SQLITE_CORRUPT_PAGE(pPage);
}
}
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
@@ -1984,6 +1926,98 @@ static int btreeInitPage(MemPage *pPage){
return SQLITE_CORRUPT_PAGE(pPage);
}
pPage->nFree = (u16)(nFree - iCellFirst);
return SQLITE_OK;
}
/*
** Initialize the auxiliary information for a disk block.
**
** 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.
*/
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 iCellFirst; /* First allowable cell or freeblock offset */
int iCellLast; /* Last possible cell or freeblock offset */
assert( pPage->pBt!=0 );
assert( pPage->pBt->db!=0 );
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
assert( pPage->pgno==sqlite3PagerPagenumber(pPage->pDbPage) );
assert( pPage == sqlite3PagerGetExtra(pPage->pDbPage) );
assert( pPage->aData == sqlite3PagerGetData(pPage->pDbPage) );
assert( pPage->isInit==0 );
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_PAGE(pPage);
}
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-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_PAGE(pPage);
}
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
|| get2byteNotZero(&data[hdr+5])==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_PAGE(pPage);
}
sz = pPage->xCellSize(pPage, &data[pc]);
testcase( pc+sz==usableSize );
if( pc+sz>usableSize ){
return SQLITE_CORRUPT_PAGE(pPage);
}
}
if( !pPage->leaf ) iCellLast++;
}
pPage->nFree = -1; /* Indicate that this value is yet uncomputed */
pPage->isInit = 1;
return SQLITE_OK;
}
@@ -2127,19 +2161,18 @@ static int getAndInitPage(
if( pgno>btreePagecount(pBt) ){
rc = SQLITE_CORRUPT_BKPT;
goto getAndInitPage_error;
goto getAndInitPage_error1;
}
rc = sqlite3PagerGet(pBt->pPager, pgno, (DbPage**)&pDbPage, bReadOnly);
if( rc ){
goto getAndInitPage_error;
goto getAndInitPage_error1;
}
*ppPage = (MemPage*)sqlite3PagerGetExtra(pDbPage);
if( (*ppPage)->isInit==0 ){
btreePageFromDbPage(pDbPage, pgno, pBt);
rc = btreeInitPage(*ppPage);
if( rc!=SQLITE_OK ){
releasePage(*ppPage);
goto getAndInitPage_error;
goto getAndInitPage_error2;
}
}
assert( (*ppPage)->pgno==pgno );
@@ -2149,12 +2182,13 @@ static int getAndInitPage(
** compatible with the root page. */
if( pCur && ((*ppPage)->nCell<1 || (*ppPage)->intKey!=pCur->curIntKey) ){
rc = SQLITE_CORRUPT_PGNO(pgno);
releasePage(*ppPage);
goto getAndInitPage_error;
goto getAndInitPage_error2;
}
return SQLITE_OK;
getAndInitPage_error:
getAndInitPage_error2:
releasePage(*ppPage);
getAndInitPage_error1:
if( pCur ){
pCur->iPage--;
pCur->pPage = pCur->apPage[pCur->iPage];
@@ -6566,6 +6600,7 @@ static void dropCell(MemPage *pPage, int idx, int sz, int *pRC){
assert( CORRUPT_DB || sz==cellSize(pPage, idx) );
assert( sqlite3PagerIswriteable(pPage->pDbPage) );
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
assert( pPage->nFree>=0 );
data = pPage->aData;
ptr = &pPage->aCellIdx[2*idx];
pc = get2byte(ptr);
@@ -6636,6 +6671,7 @@ static void insertCell(
** might be less than 8 (leaf-size + pointer) on the interior node. Hence
** the term after the || in the following assert(). */
assert( sz==pPage->xCellSize(pPage, pCell) || (sz==8 && iChild>0) );
assert( pPage->nFree>=0 );
if( pPage->nOverflow || sz+2>pPage->nFree ){
if( pTemp ){
memcpy(pTemp, pCell, sz);
@@ -7187,8 +7223,17 @@ static int balance_quick(MemPage *pParent, MemPage *pPage, u8 *pSpace){
assert( sqlite3_mutex_held(pPage->pBt->mutex) );
assert( sqlite3PagerIswriteable(pParent->pDbPage) );
assert( pPage->nOverflow==1 );
if( pPage->nCell==0 ) return SQLITE_CORRUPT_BKPT; /* dbfuzz001.test */
if( pPage->nFree<0 ){
rc = btreeComputeFreeSpace(pPage);
if( rc ) return rc;
}
if( pParent->nFree<0 ){
rc = btreeComputeFreeSpace(pParent);
if( rc ) return rc;
}
/* Allocate a new page. This page will become the right-sibling of
** pPage. Make the parent page writable, so that the new divider cell
@@ -7466,6 +7511,10 @@ static int balance_nonroot(
if( !aOvflSpace ){
return SQLITE_NOMEM_BKPT;
}
if( pParent->nFree<0 ){
rc = btreeComputeFreeSpace(pParent);
if( rc ) return rc;
}
/* Find the sibling pages to balance. Also locate the cells in pParent
** that divide the siblings. An attempt is made to find NN siblings on
@@ -7501,6 +7550,9 @@ static int balance_nonroot(
pgno = get4byte(pRight);
while( 1 ){
rc = getAndInitPage(pBt, pgno, &apOld[i], 0, 0);
if( rc==0 && apOld[i]->nFree<0 ){
rc = btreeComputeFreeSpace(apOld[i]);
}
if( rc ){
memset(apOld, 0, (i+1)*sizeof(MemPage*));
goto balance_cleanup;
@@ -7704,6 +7756,7 @@ static int balance_nonroot(
b.apEnd[k] = pParent->aDataEnd;
b.ixNx[k] = cntOld[i]+1;
}
assert( p->nFree>=0 );
szNew[i] = usableSpace - p->nFree;
for(j=0; j<p->nOverflow; j++){
szNew[i] += 2 + p->xCellSize(p, p->apOvfl[j]);
@@ -8247,6 +8300,10 @@ static int balance(BtCursor *pCur){
int iPage = pCur->iPage;
MemPage *pPage = pCur->pPage;
if( pPage->nFree<0 ){
rc = btreeComputeFreeSpace(pPage);
if( rc ) break;
}
if( iPage==0 ){
if( pPage->nOverflow ){
/* The root page of the b-tree is overfull. In this case call the
@@ -8621,6 +8678,10 @@ int sqlite3BtreeInsert(
pPage = pCur->pPage;
assert( pPage->intKey || pX->nKey>=0 );
assert( pPage->leaf || !pPage->intKey );
if( pPage->nFree<0 ){
rc = btreeComputeFreeSpace(pPage);
if( rc ) return rc;
}
TRACE(("INSERT: table=%d nkey=%lld ndata=%d page=%d %s\n",
pCur->pgnoRoot, pX->nKey, pX->nData, pPage->pgno,
@@ -8771,6 +8832,7 @@ int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
iCellIdx = pCur->ix;
pPage = pCur->pPage;
pCell = findCell(pPage, iCellIdx);
if( pPage->nFree<0 && btreeComputeFreeSpace(pPage) ) return SQLITE_CORRUPT;
/* If the bPreserve flag is set to true, then the cursor position must
** be preserved following this delete operation. If the current delete
@@ -8841,6 +8903,10 @@ int sqlite3BtreeDelete(BtCursor *pCur, u8 flags){
Pgno n;
unsigned char *pTmp;
if( pLeaf->nFree<0 ){
rc = btreeComputeFreeSpace(pLeaf);
if( rc ) return rc;
}
if( iCellDepth<pCur->iPage-1 ){
n = pCur->apPage[iCellDepth+1]->pgno;
}else{
@@ -9732,6 +9798,11 @@ static int checkTreePage(
"btreeInitPage() returns error code %d", rc);
goto end_of_check;
}
if( (rc = btreeComputeFreeSpace(pPage))!=0 ){
assert( rc==SQLITE_CORRUPT );
checkAppendMsg(pCheck, "free space corruption", rc);
goto end_of_check;
}
data = pPage->aData;
hdr = pPage->hdrOffset;