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Add the SQLITE_IOCAP_BYPASS device characteristic. Do not allow the

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SQLITE_DIRECT_OVERFLOW_READ optimization if that capability is missing.

FossilOrigin-Name: f50ae00ce9ff572e6bd5e2788602ba356383526ab7289622a32fbf52926c6df0
This commit is contained in:
drh
2024-10-22 18:00:26 +00:00
parent 76e48f4d66
commit c8284c766a
6 changed files with 36 additions and 17 deletions
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1
src/os_unix.c
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@ -4128,6 +4128,7 @@ static void setDeviceCharacteristics(unixFile *pFd){
if( pFd->ctrlFlags & UNIXFILE_PSOW ){
pFd->deviceCharacteristics |= SQLITE_IOCAP_POWERSAFE_OVERWRITE;
}
pFd->deviceCharacteristics |= SQLITE_IOCAP_BYPASS;
pFd->sectorSize = SQLITE_DEFAULT_SECTOR_SIZE;
}

2
src/os_win.c
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@ -3660,7 +3660,7 @@ static int winSectorSize(sqlite3_file *id){
*/
static int winDeviceCharacteristics(sqlite3_file *id){
winFile *p = (winFile*)id;
return SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN |
return SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN | SQLITE_IOCAP_BYPASS |
((p->ctrlFlags & WINFILE_PSOW)?SQLITE_IOCAP_POWERSAFE_OVERWRITE:0);
}

20
src/pager.c
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@ -808,18 +808,26 @@ static const unsigned char aJournalMagic[] = {
** Return true if page pgno can be read directly from the database file
** by the b-tree layer. This is the case if:
**
** * the database file is open,
** * there are no dirty pages in the cache, and
** * the desired page is not currently in the wal file.
** (1) the database file is open
** (2) the VFS for the database has BYPASS capability
** (3) there are no dirty pages in the cache, and
** (4) the desired page is not currently in the wal file.
*/
int sqlite3PagerDirectReadOk(Pager *pPager, Pgno pgno){
if( pPager->fd->pMethods==0 ) return 0;
if( sqlite3PCacheIsDirty(pPager->pPCache) ) return 0;
assert( pPager!=0 );
assert( pPager->fd!=0 );
if( pPager->fd->pMethods==0 ) return 0; /* Case (1) */
assert( pPager->fd->pMethods->xDeviceCharacteristics!=0 );
if( (pPager->fd->pMethods->xDeviceCharacteristics(pPager->fd)
& SQLITE_IOCAP_BYPASS)==0 ){
return 0; /* Case (2) */
}
if( sqlite3PCacheIsDirty(pPager->pPCache) ) return 0; /* Failed (3) */
#ifndef SQLITE_OMIT_WAL
if( pPager->pWal ){
u32 iRead = 0;
(void)sqlite3WalFindFrame(pPager->pWal, pgno, &iRead);
return iRead==0;
return iRead==0; /* Condition (4) */
}
#endif
return 1;

7
src/sqlite.h.in
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@ -652,6 +652,11 @@ int sqlite3_exec(
** filesystem supports doing multiple write operations atomically when those
** write operations are bracketed by [SQLITE_FCNTL_BEGIN_ATOMIC_WRITE] and
** [SQLITE_FCNTL_COMMIT_ATOMIC_WRITE].
**
** The SQLITE_IOCAP_BYPASS property means that it is ok for the
** B-tree layer to bypass the pager and VFS and read content directly
** from the filesystem (the SQLITE_DIRECT_OVERFLOW_READ optimization)
** when that is beneficial for performance.
*/
#define SQLITE_IOCAP_ATOMIC 0x00000001
#define SQLITE_IOCAP_ATOMIC512 0x00000002
@ -668,6 +673,7 @@ int sqlite3_exec(
#define SQLITE_IOCAP_POWERSAFE_OVERWRITE 0x00001000
#define SQLITE_IOCAP_IMMUTABLE 0x00002000
#define SQLITE_IOCAP_BATCH_ATOMIC 0x00004000
#define SQLITE_IOCAP_BYPASS 0x00008000
/*
** CAPI3REF: File Locking Levels
@ -814,6 +820,7 @@ struct sqlite3_file {
** <li> [SQLITE_IOCAP_POWERSAFE_OVERWRITE]
** <li> [SQLITE_IOCAP_IMMUTABLE]
** <li> [SQLITE_IOCAP_BATCH_ATOMIC]
** <li> [SQLITE_IOCAP_BYPASS]
** </ul>
**
** The SQLITE_IOCAP_ATOMIC property means that all writes of