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Small performance improvement and size reduction for pageFindSlot() - the

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routine in btree.c that locates a free slot for a cell on a btree page.

FossilOrigin-Name: 1969372ac72d25cc642a0268f4bb0ae4b59f2dca568c119ef61b67183b3a8bd9
This commit is contained in:
drh
2019-02-08 22:34:59 +00:00
parent 16d7e87caa
commit 298f45c641
3 changed files with 30 additions and 23 deletions
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39
src/btree.c
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@@ -1533,16 +1533,16 @@ static int defragmentPage(MemPage *pPage, int nMaxFrag){
** causes the fragmentation count to exceed 60.
*/
static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc){
const int hdr = pPg->hdrOffset;
u8 * const aData = pPg->aData;
int iAddr = hdr + 1;
int pc = get2byte(&aData[iAddr]);
int x;
int usableSize = pPg->pBt->usableSize;
int size; /* Size of the free slot */
const int hdr = pPg->hdrOffset; /* Offset to page header */
u8 * const aData = pPg->aData; /* Page data */
int iAddr = hdr + 1; /* Address of ptr to pc */
int pc = get2byte(&aData[iAddr]); /* Address of a free slot */
int x; /* Excess size of the slot */
int maxPC = pPg->pBt->usableSize - nByte; /* Max address for a usable slot */
int size; /* Size of the free slot */
assert( pc>0 );
while( pc<=usableSize-4 ){
while( pc<=maxPC ){
/* EVIDENCE-OF: R-22710-53328 The third and fourth bytes of each
** freeblock form a big-endian integer which is the size of the freeblock
** in bytes, including the 4-byte header. */
@@ -1550,10 +1550,7 @@ static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc){
if( (x = size - nByte)>=0 ){
testcase( x==4 );
testcase( x==3 );
if( size+pc > usableSize ){
*pRc = SQLITE_CORRUPT_PAGE(pPg);
return 0;
}else if( x<4 ){
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]>57 ) return 0;
@@ -1562,21 +1559,31 @@ static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc){
** fragmented bytes within the page. */
memcpy(&aData[iAddr], &aData[pc], 2);
aData[hdr+7] += (u8)x;
}else if( x+pc > maxPC ){
/* This slot extends off the end of the usable part of the page */
*pRc = SQLITE_CORRUPT_PAGE(pPg);
return 0;
}else{
/* The slot remains on the free-list. Reduce its size to account
** for the portion used by the new allocation. */
** for the portion used by the new allocation. */
put2byte(&aData[pc+2], x);
}
return &aData[pc + x];
}
iAddr = pc;
pc = get2byte(&aData[pc]);
if( pc<iAddr+size ) break;
if( pc<iAddr+size ){
if( pc ){
/* The next slot in the chain is not past the end of the current slot */
*pRc = SQLITE_CORRUPT_PAGE(pPg);
}
return 0;
}
}
if( pc ){
if( pc>maxPC+nByte-4 ){
/* The free slot chain extends off the end of the page */
*pRc = SQLITE_CORRUPT_PAGE(pPg);
}
return 0;
}