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Remove the requirement to open the wal file before sqlite3_snapshot_recover()

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is called. Also add some comments to new functions.

FossilOrigin-Name: 28393c413cc4505b94411730e728583c5d4baaae
This commit is contained in:
dan
2016-11-19 18:31:37 +00:00
parent 4d4757fcc8
commit 93f5113290
6 changed files with 86 additions and 61 deletions
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104
src/wal.c
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@@ -2380,70 +2380,76 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
}
/*
** Recover as many snapshots as possible from the wal file.
** Attempt to reduce the value of the WalCkptInfo.nBackfillAttempted
** variable so that older snapshots can be accessed. To do this, loop
** through all wal frames from nBackfillAttempted to (nBackfill+1),
** comparing their content to the corresponding page with the database
** file, if any. Set nBackfillAttempted to the frame number of the
** first frame for which the wal file content matches the db file.
**
** This is only really safe if the file-system is such that any page
** writes made by earlier checkpointers were atomic operations, which
** is not always true. It is also possible that nBackfillAttempted
** may be left set to a value larger than expected, if a wal frame
** contains content that duplicate of an earlier version of the same
** page.
**
** SQLITE_OK is returned if successful, or an SQLite error code if an
** error occurs. It is not an error if nBackfillAttempted cannot be
** decreased at all.
*/
int sqlite3WalSnapshotRecover(Wal *pWal){
int dummy;
int rc;
rc = sqlite3WalBeginReadTransaction(pWal, &dummy);
assert( pWal->readLock>=0 );
rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
if( rc==SQLITE_OK ){
rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
int szPage = (int)pWal->szPage;
i64 szDb; /* Size of db file in bytes */
rc = sqlite3OsFileSize(pWal->pDbFd, &szDb);
if( rc==SQLITE_OK ){
volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
int szPage = (int)pWal->szPage;
i64 szDb; /* Size of db file in bytes */
void *pBuf1 = sqlite3_malloc(szPage);
void *pBuf2 = sqlite3_malloc(szPage);
if( pBuf1==0 || pBuf2==0 ){
rc = SQLITE_NOMEM;
}else{
u32 i = pInfo->nBackfillAttempted;
for(i=pInfo->nBackfillAttempted; i>pInfo->nBackfill; i--){
volatile ht_slot *dummy;
volatile u32 *aPgno; /* Array of page numbers */
u32 iZero; /* Frame corresponding to aPgno[0] */
u32 pgno; /* Page number in db file */
i64 iDbOff; /* Offset of db file entry */
i64 iWalOff; /* Offset of wal file entry */
rc = sqlite3OsFileSize(pWal->pDbFd, &szDb);
if( rc==SQLITE_OK ){
void *pBuf1 = sqlite3_malloc(szPage);
void *pBuf2 = sqlite3_malloc(szPage);
if( pBuf1==0 || pBuf2==0 ){
rc = SQLITE_NOMEM;
}else{
u32 i = pInfo->nBackfillAttempted;
for(i=pInfo->nBackfillAttempted; i>pInfo->nBackfill; i--){
volatile ht_slot *dummy;
volatile u32 *aPgno; /* Array of page numbers */
u32 iZero; /* Frame corresponding to aPgno[0] */
u32 pgno; /* Page number in db file */
i64 iDbOff; /* Offset of db file entry */
i64 iWalOff; /* Offset of wal file entry */
rc = walHashGet(pWal, walFramePage(i), &dummy, &aPgno, &iZero);
if( rc!=SQLITE_OK ) break;
pgno = aPgno[i-iZero];
iDbOff = (i64)(pgno-1) * szPage;
rc = walHashGet(pWal, walFramePage(i), &dummy, &aPgno, &iZero);
if( rc!=SQLITE_OK ) break;
pgno = aPgno[i-iZero];
iDbOff = (i64)(pgno-1) * szPage;
if( iDbOff+szPage<=szDb ){
iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
if( iDbOff+szPage<=szDb ){
iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
if( rc==SQLITE_OK ){
rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
}
if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
break;
}
if( rc==SQLITE_OK ){
rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
}
pInfo->nBackfillAttempted = i-1;
if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
break;
}
}
pInfo->nBackfillAttempted = i-1;
}
sqlite3_free(pBuf1);
sqlite3_free(pBuf2);
}
walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
}
/* End the read transaction opened above. Also zero the cache of the
** wal-index header to force the pager-cache to be flushed when the next
** read transaction is open, as it may not match the current contents of
** pWal->hdr. */
sqlite3WalEndReadTransaction(pWal);
memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
sqlite3_free(pBuf1);
sqlite3_free(pBuf2);
}
walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
}
return rc;