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Overview
| Comment: | Small performance improvement and size reduction for pageFindSlot() - the routine in btree.c that locates a free slot for a cell on a btree page. |
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| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
1969372ac72d25cc642a0268f4bb0ae4 |
| User & Date: | drh 2019-02-08 22:34:59.960 |
Context
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2019-02-09
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| 19:23 | Change a few assert() statements in fts3 that might fail if the database is corrupt. (check-in: db74a56af7 user: dan tags: trunk) | |
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2019-02-08
| ||
| 22:34 | Small performance improvement and size reduction for pageFindSlot() - the routine in btree.c that locates a free slot for a cell on a btree page. (check-in: 1969372ac7 user: drh tags: trunk) | |
| 17:28 | Further simplifications to sqlite3VdbeMemSetStr(). (check-in: 1d21295707 user: drh tags: trunk) | |
Changes
Changes to src/btree.c.
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** detected then *pRc is set to SQLITE_CORRUPT and NULL is returned.
**
** Slots on the free list that are between 1 and 3 bytes larger than nByte
** will be ignored if adding the extra space to the fragmentation count
** causes the fragmentation count to exceed 60.
*/
static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc){
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** detected then *pRc is set to SQLITE_CORRUPT and NULL is returned.
**
** Slots on the free list that are between 1 and 3 bytes larger than nByte
** will be ignored if adding the extra space to the fragmentation count
** causes the fragmentation count to exceed 60.
*/
static u8 *pageFindSlot(MemPage *pPg, int nByte, int *pRc){
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<=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. */
size = get2byte(&aData[pc+2]);
if( (x = size - nByte)>=0 ){
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]>57 ) return 0;
/* Remove the slot from the free-list. Update the number of
** 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. */
put2byte(&aData[pc+2], x);
}
return &aData[pc + x];
}
iAddr = pc;
pc = get2byte(&aData[pc]);
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>maxPC+nByte-4 ){
/* The free slot chain extends off the end of the page */
*pRc = SQLITE_CORRUPT_PAGE(pPg);
}
return 0;
}
/*
** Allocate nByte bytes of space from within the B-Tree page passed
** as the first argument. Write into *pIdx the index into pPage->aData[]
** of the first byte of allocated space. Return either SQLITE_OK or
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