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-rw-r--r--src/btree.c102
1 files changed, 82 insertions, 20 deletions
diff --git a/src/btree.c b/src/btree.c
index f61078cac..5ae5986cf 100644
--- a/src/btree.c
+++ b/src/btree.c
@@ -1139,6 +1139,11 @@ static void ptrmapPutOvflPtr(MemPage *pPage, u8 *pCell, int *pRC){
** 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.
+**
+** EVIDENCE-OF: R-44582-60138 SQLite may from time to time reorganize a
+** b-tree page so that there are no freeblocks or fragment bytes, all
+** unused bytes are contained in the unallocated space region, and all
+** cells are packed tightly at the end of the page.
*/
static int defragmentPage(MemPage *pPage){
int i; /* Loop counter */
@@ -1262,6 +1267,8 @@ static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc, int *pbDefrag){
testcase( x==4 );
testcase( x==3 );
if( x<4 ){
+ /* EVIDENCE-OF: R-11498-58022 In a well-formed b-tree page, the total
+ ** number of bytes in fragments may not exceed 60. */
if( aData[hdr+7]>=60 ){
if( pbDefrag ) *pbDefrag = 1;
return 0;
@@ -1316,19 +1323,13 @@ static int allocateSpace(MemPage *pPage, int nByte, int *pIdx){
assert( pPage->cellOffset == hdr + 12 - 4*pPage->leaf );
gap = pPage->cellOffset + 2*pPage->nCell;
assert( gap<=65536 );
- top = get2byte(&data[hdr+5]);
- if( gap>top ){
- if( top==0 ){
- /* EVIDENCE-OF: R-29356-02391 If the database uses a 65536-byte page size
- ** and the reserved space is zero (the usual value for reserved space)
- ** then the cell content offset of an empty page wants to be 65536.
- ** However, that integer is too large to be stored in a 2-byte unsigned
- ** integer, so a value of 0 is used in its place. */
- top = 65536;
- }else{
- return SQLITE_CORRUPT_BKPT;
- }
- }
+ /* EVIDENCE-OF: R-29356-02391 If the database uses a 65536-byte page size
+ ** and the reserved space is zero (the usual value for reserved space)
+ ** then the cell content offset of an empty page wants to be 65536.
+ ** However, that integer is too large to be stored in a 2-byte unsigned
+ ** integer, so a value of 0 is used in its place. */
+ top = get2byteNotZero(&data[hdr+5]);
+ if( gap>top ) return SQLITE_CORRUPT_BKPT;
/* If there is enough space between gap and top for one more cell pointer
** array entry offset, and if the freelist is not empty, then search the
@@ -1497,18 +1498,32 @@ static int decodeFlags(MemPage *pPage, int flagByte){
pPage->childPtrSize = 4-4*pPage->leaf;
pBt = pPage->pBt;
if( flagByte==(PTF_LEAFDATA | PTF_INTKEY) ){
+ /* EVIDENCE-OF: R-03640-13415 A value of 5 means the page is an interior
+ ** table b-tree page. */
+ assert( (PTF_LEAFDATA|PTF_INTKEY)==5 );
+ /* EVIDENCE-OF: R-20501-61796 A value of 13 means the page is a leaf
+ ** table b-tree page. */
+ assert( (PTF_LEAFDATA|PTF_INTKEY|PTF_LEAF)==13 );
pPage->intKey = 1;
pPage->intKeyLeaf = pPage->leaf;
pPage->noPayload = !pPage->leaf;
pPage->maxLocal = pBt->maxLeaf;
pPage->minLocal = pBt->minLeaf;
}else if( flagByte==PTF_ZERODATA ){
+ /* EVIDENCE-OF: R-27225-53936 A value of 2 means the page is an interior
+ ** index b-tree page. */
+ assert( (PTF_ZERODATA)==2 );
+ /* EVIDENCE-OF: R-16571-11615 A value of 10 means the page is a leaf
+ ** index b-tree page. */
+ assert( (PTF_ZERODATA|PTF_LEAF)==10 );
pPage->intKey = 0;
pPage->intKeyLeaf = 0;
pPage->noPayload = 0;
pPage->maxLocal = pBt->maxLocal;
pPage->minLocal = pBt->minLocal;
}else{
+ /* EVIDENCE-OF: R-47608-56469 Any other value for the b-tree page type is
+ ** an error. */
return SQLITE_CORRUPT_BKPT;
}
pPage->max1bytePayload = pBt->max1bytePayload;
@@ -1548,21 +1563,33 @@ static int btreeInitPage(MemPage *pPage){
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 + 12 - 4*pPage->leaf;
+ pPage->cellOffset = cellOffset = hdr + 8 + pPage->childPtrSize;
pPage->aDataEnd = &data[usableSize];
pPage->aCellIdx = &data[cellOffset];
+ /* 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.
@@ -1596,13 +1623,20 @@ static int btreeInitPage(MemPage *pPage){
}
#endif
- /* Compute the total free space on the page */
+ /* 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;
+ nFree = data[hdr+7] + top; /* Init nFree to non-freeblock free space */
while( pc>0 ){
u16 next, size;
if( pc<iCellFirst || pc>iCellLast ){
- /* Start of free block is off the page */
+ /* EVIDENCE-OF: R-55530-52930 In a well-formed b-tree page, there will
+ ** always be at least one cell before the first freeblock.
+ **
+ ** Or, the freeblock is off the end of the page
+ */
return SQLITE_CORRUPT_BKPT;
}
next = get2byte(&data[pc]);
@@ -5959,9 +5993,17 @@ static void dropCell(MemPage *pPage, int idx, int sz, int *pRC){
return;
}
pPage->nCell--;
- memmove(ptr, ptr+2, 2*(pPage->nCell - idx));
- put2byte(&data[hdr+3], pPage->nCell);
- pPage->nFree += 2;
+ if( pPage->nCell==0 ){
+ memset(&data[hdr+1], 0, 4);
+ data[hdr+7] = 0;
+ put2byte(&data[hdr+5], pPage->pBt->usableSize);
+ pPage->nFree = pPage->pBt->usableSize - pPage->hdrOffset
+ - pPage->childPtrSize - 8;
+ }else{
+ memmove(ptr, ptr+2, 2*(pPage->nCell - idx));
+ put2byte(&data[hdr+3], pPage->nCell);
+ pPage->nFree += 2;
+ }
}
/*
@@ -8609,8 +8651,14 @@ static int checkTreePage(
assert( contentOffset<=usableSize ); /* Enforced by btreeInitPage() */
memset(hit+contentOffset, 0, usableSize-contentOffset);
memset(hit, 1, contentOffset);
+ /* EVIDENCE-OF: R-37002-32774 The two-byte integer at offset 3 gives the
+ ** number of cells on the page. */
nCell = get2byte(&data[hdr+3]);
+ /* EVIDENCE-OF: R-23882-45353 The cell pointer array of a b-tree page
+ ** immediately follows the b-tree page header. */
cellStart = hdr + 12 - 4*pPage->leaf;
+ /* EVIDENCE-OF: R-02776-14802 The cell pointer array consists of K 2-byte
+ ** integer offsets to the cell contents. */
for(i=0; i<nCell; i++){
int pc = get2byte(&data[cellStart+i*2]);
u32 size = 65536;
@@ -8626,6 +8674,9 @@ static int checkTreePage(
for(j=pc+size-1; j>=pc; j--) hit[j]++;
}
}
+ /* EVIDENCE-OF: R-20690-50594 The second field of the b-tree page header
+ ** is the offset of the first freeblock, or zero if there are no
+ ** freeblocks on the page. */
i = get2byte(&data[hdr+1]);
while( i>0 ){
int size, j;
@@ -8633,7 +8684,13 @@ static int checkTreePage(
size = get2byte(&data[i+2]);
assert( i+size<=usableSize ); /* Enforced by btreeInitPage() */
for(j=i+size-1; j>=i; j--) hit[j]++;
+ /* EVIDENCE-OF: R-58208-19414 The first 2 bytes of a freeblock are a
+ ** big-endian integer which is the offset in the b-tree page of the next
+ ** freeblock in the chain, or zero if the freeblock is the last on the
+ ** chain. */
j = get2byte(&data[i]);
+ /* EVIDENCE-OF: R-06866-39125 Freeblocks are always connected in order of
+ ** increasing offset. */
assert( j==0 || j>i+size ); /* Enforced by btreeInitPage() */
assert( j<=usableSize-4 ); /* Enforced by btreeInitPage() */
i = j;
@@ -8647,6 +8704,11 @@ static int checkTreePage(
break;
}
}
+ /* EVIDENCE-OF: R-43263-13491 The total number of bytes in all fragments
+ ** is stored in the fifth field of the b-tree page header.
+ ** EVIDENCE-OF: R-07161-27322 The one-byte integer at offset 7 gives the
+ ** number of fragmented free bytes within the cell content area.
+ */
if( cnt!=data[hdr+7] ){
checkAppendMsg(pCheck,
"Fragmentation of %d bytes reported as %d on page %d",
generated by cgit v1.2.3 (git 2.25.1) at 2025-07-20 02:19:43 +0000