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Add experimental sqlite3_snapshot_recover() API.

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FossilOrigin-Name: 174a6076a8d7bebe5efebf55f3fdc5d87c589cc7
This commit is contained in:
dan
2016-11-18 20:49:43 +00:00
parent edace5d4f1
commit 1158498dce
10 changed files with 221 additions and 15 deletions
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65
src/wal.c
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@@ -2379,6 +2379,65 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
return rc;
}
/*
** Recover as many snapshots as possible from the wal file.
*/
int sqlite3WalSnapshotRecover(Wal *pWal){
int dummy;
int rc;
rc = sqlite3WalBeginReadTransaction(pWal, &dummy);
if( rc==SQLITE_OK ){
rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
if( rc==SQLITE_OK ){
volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
int szPage = (int)pWal->szPage;
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 ){
pgno = aPgno[i-iZero];
iDbOff = (i64)(pgno-1) * szPage;
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;
}
pInfo->nBackfillAttempted = i-1;
}
}
sqlite3_free(pBuf1);
sqlite3_free(pBuf2);
walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
}
sqlite3WalEndReadTransaction(pWal);
}
return rc;
}
/*
** Begin a read transaction on the database.
**
@@ -2441,7 +2500,11 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
** has not yet set the pInfo->nBackfillAttempted variable to indicate
** its intent. To avoid the race condition this leads to, ensure that
** there is no checkpointer process by taking a shared CKPT lock
** before checking pInfo->nBackfillAttempted. */
** before checking pInfo->nBackfillAttempted.
**
** TODO: Does the aReadMark[] lock prevent a checkpointer from doing
** this already?
*/
rc = walLockShared(pWal, WAL_CKPT_LOCK);
if( rc==SQLITE_OK ){