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Overview
| Comment: | Another size and performance optimization to readDbPage(). This time we eliminate some unnecessary local variables. |
|---|---|
| Downloads: | Tarball | ZIP archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
745bc8decd18d4dc00589474fd3928a3 |
| User & Date: | drh 2017-08-18 22:30:20.164 |
Context
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2017-08-19
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| 20:38 | Space and size optimization to the printf implementation. (check-in: d01d2cffef user: drh tags: trunk) | |
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2017-08-18
| ||
| 22:30 | Another size and performance optimization to readDbPage(). This time we eliminate some unnecessary local variables. (check-in: 745bc8decd user: drh tags: trunk) | |
| 21:14 | Size and performance optimization the readDbPage() routine in the pager. (check-in: ca9e1875c3 user: drh tags: trunk) | |
Changes
Changes to src/pager.c.
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** the value read from the database file.
**
** If an IO error occurs, then the IO error is returned to the caller.
** Otherwise, SQLITE_OK is returned.
*/
static int readDbPage(PgHdr *pPg){
Pager *pPager = pPg->pPager; /* Pager object associated with page pPg */
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** the value read from the database file.
**
** If an IO error occurs, then the IO error is returned to the caller.
** Otherwise, SQLITE_OK is returned.
*/
static int readDbPage(PgHdr *pPg){
Pager *pPager = pPg->pPager; /* Pager object associated with page pPg */
int rc = SQLITE_OK; /* Return code */
u32 iFrame = 0; /* Frame of WAL containing pgno */
assert( pPager->eState>=PAGER_READER && !MEMDB );
assert( isOpen(pPager->fd) );
if( pagerUseWal(pPager) ){
rc = sqlite3WalFindFrame(pPager->pWal, pPg->pgno, &iFrame);
if( rc ) return rc;
}
if( iFrame ){
rc = sqlite3WalReadFrame(pPager->pWal, iFrame,pPager->pageSize,pPg->pData);
}else{
i64 iOffset = (pPg->pgno-1)*(i64)pPager->pageSize;
rc = sqlite3OsRead(pPager->fd, pPg->pData, pPager->pageSize, iOffset);
if( rc==SQLITE_IOERR_SHORT_READ ){
rc = SQLITE_OK;
}
}
if( pPg->pgno==1 ){
if( rc ){
/* If the read is unsuccessful, set the dbFileVers[] to something
** that will never be a valid file version. dbFileVers[] is a copy
** of bytes 24..39 of the database. Bytes 28..31 should always be
** zero or the size of the database in page. Bytes 32..35 and 35..39
** should be page numbers which are never 0xffffffff. So filling
** pPager->dbFileVers[] with all 0xff bytes should suffice.
**
** For an encrypted database, the situation is more complex: bytes
** 24..39 of the database are white noise. But the probability of
** white noise equaling 16 bytes of 0xff is vanishingly small so
** we should still be ok.
*/
memset(pPager->dbFileVers, 0xff, sizeof(pPager->dbFileVers));
}else{
u8 *dbFileVers = &((u8*)pPg->pData)[24];
memcpy(&pPager->dbFileVers, dbFileVers, sizeof(pPager->dbFileVers));
}
}
CODEC1(pPager, pPg->pData, pPg->pgno, 3, rc = SQLITE_NOMEM_BKPT);
PAGER_INCR(sqlite3_pager_readdb_count);
PAGER_INCR(pPager->nRead);
IOTRACE(("PGIN %p %d\n", pPager, pPg->pgno));
PAGERTRACE(("FETCH %d page %d hash(%08x)\n",
PAGERID(pPager), pPg->pgno, pager_pagehash(pPg)));
return rc;
}
/*
** Update the value of the change-counter at offsets 24 and 92 in
** the header and the sqlite version number at offset 96.
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