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-rw-r--r--src/wal.c331
1 files changed, 184 insertions, 147 deletions
diff --git a/src/wal.c b/src/wal.c
index fd2eabfd9..41018b584 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -44,7 +44,7 @@
** 28: Checksum-2 (second part of checksum for first 24 bytes of header).
**
** Immediately following the wal-header are zero or more frames. Each
-** frame consists of a 24-byte frame-header followed by a <page-size> bytes
+** frame consists of a 24-byte frame-header followed by <page-size> bytes
** of page data. The frame-header is six big-endian 32-bit unsigned
** integer values, as follows:
**
@@ -502,6 +502,11 @@ struct WalCkptInfo {
/*
** An open write-ahead log file is represented by an instance of the
** following object.
+**
+** writeLock:
+** This is usually set to 1 whenever the WRITER lock is held. However,
+** if it is set to 2, then the WRITER lock is held but must be released
+** by walHandleException() if a SEH exception is thrown.
*/
struct Wal {
sqlite3_vfs *pVfs; /* The VFS used to create pDbFd */
@@ -541,6 +546,7 @@ struct Wal {
#endif
#ifdef SQLITE_ENABLE_SNAPSHOT
WalIndexHdr *pSnapshot; /* Start transaction here if not NULL */
+ int bGetSnapshot; /* Transaction opened for sqlite3_get_snapshot() */
#endif
#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
sqlite3 *db;
@@ -591,9 +597,13 @@ struct WalIterator {
u32 *aPgno; /* Array of page numbers. */
int nEntry; /* Nr. of entries in aPgno[] and aIndex[] */
int iZero; /* Frame number associated with aPgno[0] */
- } aSegment[1]; /* One for every 32KB page in the wal-index */
+ } aSegment[FLEXARRAY]; /* One for every 32KB page in the wal-index */
};
+/* Size (in bytes) of a WalIterator object suitable for N or fewer segments */
+#define SZ_WALITERATOR(N) \
+ (offsetof(WalIterator,aSegment)*(N)*sizeof(struct WalSegment))
+
/*
** Define the parameters of the hash tables in the wal-index file. There
** is a hash-table following every HASHTABLE_NPAGE page numbers in the
@@ -752,7 +762,7 @@ static SQLITE_NOINLINE int walIndexPageRealloc(
/* Enlarge the pWal->apWiData[] array if required */
if( pWal->nWiData<=iPage ){
- sqlite3_int64 nByte = sizeof(u32*)*(iPage+1);
+ sqlite3_int64 nByte = sizeof(u32*)*(1+(i64)iPage);
volatile u32 **apNew;
apNew = (volatile u32 **)sqlite3Realloc((void *)pWal->apWiData, nByte);
if( !apNew ){
@@ -861,10 +871,8 @@ static void walChecksumBytes(
s1 = s2 = 0;
}
- assert( nByte>=8 );
- assert( (nByte&0x00000007)==0 );
- assert( nByte<=65536 );
- assert( nByte%4==0 );
+ /* nByte is a multiple of 8 between 8 and 65536 */
+ assert( nByte>=8 && (nByte&7)==0 && nByte<=65536 );
if( !nativeCksum ){
do {
@@ -1954,8 +1962,7 @@ static int walIteratorInit(Wal *pWal, u32 nBackfill, WalIterator **pp){
/* Allocate space for the WalIterator object. */
nSegment = walFramePage(iLast) + 1;
- nByte = sizeof(WalIterator)
- + (nSegment-1)*sizeof(struct WalSegment)
+ nByte = SZ_WALITERATOR(nSegment)
+ iLast*sizeof(ht_slot);
p = (WalIterator *)sqlite3_malloc64(nByte
+ sizeof(ht_slot) * (iLast>HASHTABLE_NPAGE?HASHTABLE_NPAGE:iLast)
@@ -2026,7 +2033,7 @@ static int walEnableBlockingMs(Wal *pWal, int nMs){
static int walEnableBlocking(Wal *pWal){
int res = 0;
if( pWal->db ){
- int tmout = pWal->db->busyTimeout;
+ int tmout = pWal->db->setlkTimeout;
if( tmout ){
res = walEnableBlockingMs(pWal, tmout);
}
@@ -2412,7 +2419,9 @@ static int walHandleException(Wal *pWal){
static const int S = 1;
static const int E = (1<<SQLITE_SHM_NLOCK);
int ii;
- u32 mUnlock = pWal->lockMask & ~(
+ u32 mUnlock;
+ if( pWal->writeLock==2 ) pWal->writeLock = 0;
+ mUnlock = pWal->lockMask & ~(
(pWal->readLock<0 ? 0 : (S << WAL_READ_LOCK(pWal->readLock)))
| (pWal->writeLock ? (E << WAL_WRITE_LOCK) : 0)
| (pWal->ckptLock ? (E << WAL_CKPT_LOCK) : 0)
@@ -2433,7 +2442,7 @@ static int walHandleException(Wal *pWal){
/*
** Assert that the Wal.lockMask mask, which indicates the locks held
-** by the connenction, is consistent with the Wal.readLock, Wal.writeLock
+** by the connection, is consistent with the Wal.readLock, Wal.writeLock
** and Wal.ckptLock variables. To be used as:
**
** assert( walAssertLockmask(pWal) );
@@ -2684,7 +2693,12 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){
if( bWriteLock
|| SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1))
){
- pWal->writeLock = 1;
+ /* If the write-lock was just obtained, set writeLock to 2 instead of
+ ** the usual 1. This causes walIndexPage() to behave as if the
+ ** write-lock were held (so that it allocates new pages as required),
+ ** and walHandleException() to unlock the write-lock if a SEH exception
+ ** is thrown. */
+ if( !bWriteLock ) pWal->writeLock = 2;
if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){
badHdr = walIndexTryHdr(pWal, pChanged);
if( badHdr ){
@@ -2985,11 +2999,7 @@ static int walBeginShmUnreliable(Wal *pWal, int *pChanged){
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
volatile WalCkptInfo *pInfo; /* Checkpoint information in wal-index */
- u32 mxReadMark; /* Largest aReadMark[] value */
- int mxI; /* Index of largest aReadMark[] value */
- int i; /* Loop counter */
int rc = SQLITE_OK; /* Return code */
- u32 mxFrame; /* Wal frame to lock to */
#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
int nBlockTmout = 0;
#endif
@@ -3052,7 +3062,6 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
rc = walIndexReadHdr(pWal, pChanged);
}
#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
- walDisableBlocking(pWal);
if( rc==SQLITE_BUSY_TIMEOUT ){
rc = SQLITE_BUSY;
*pCnt |= WAL_RETRY_BLOCKED_MASK;
@@ -3067,6 +3076,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
** WAL_RETRY this routine will be called again and will probably be
** right on the second iteration.
*/
+ (void)walEnableBlocking(pWal);
if( pWal->apWiData[0]==0 ){
/* This branch is taken when the xShmMap() method returns SQLITE_BUSY.
** We assume this is a transient condition, so return WAL_RETRY. The
@@ -3083,6 +3093,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
rc = SQLITE_BUSY_RECOVERY;
}
}
+ walDisableBlocking(pWal);
if( rc!=SQLITE_OK ){
return rc;
}
@@ -3095,141 +3106,147 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int *pCnt){
assert( pWal->apWiData[0]!=0 );
pInfo = walCkptInfo(pWal);
SEH_INJECT_FAULT;
- if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame
+ {
+ u32 mxReadMark; /* Largest aReadMark[] value */
+ int mxI; /* Index of largest aReadMark[] value */
+ int i; /* Loop counter */
+ u32 mxFrame; /* Wal frame to lock to */
+ if( !useWal && AtomicLoad(&pInfo->nBackfill)==pWal->hdr.mxFrame
#ifdef SQLITE_ENABLE_SNAPSHOT
- && (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0)
+ && ((pWal->bGetSnapshot==0 && pWal->pSnapshot==0) || pWal->hdr.mxFrame==0)
#endif
- ){
- /* The WAL has been completely backfilled (or it is empty).
- ** and can be safely ignored.
- */
- rc = walLockShared(pWal, WAL_READ_LOCK(0));
- walShmBarrier(pWal);
- if( rc==SQLITE_OK ){
- if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
- /* It is not safe to allow the reader to continue here if frames
- ** may have been appended to the log before READ_LOCK(0) was obtained.
- ** When holding READ_LOCK(0), the reader ignores the entire log file,
- ** which implies that the database file contains a trustworthy
- ** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from
- ** happening, this is usually correct.
- **
- ** However, if frames have been appended to the log (or if the log
- ** is wrapped and written for that matter) before the READ_LOCK(0)
- ** is obtained, that is not necessarily true. A checkpointer may
- ** have started to backfill the appended frames but crashed before
- ** it finished. Leaving a corrupt image in the database file.
- */
- walUnlockShared(pWal, WAL_READ_LOCK(0));
- return WAL_RETRY;
+ ){
+ /* The WAL has been completely backfilled (or it is empty).
+ ** and can be safely ignored.
+ */
+ rc = walLockShared(pWal, WAL_READ_LOCK(0));
+ walShmBarrier(pWal);
+ if( rc==SQLITE_OK ){
+ if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr,sizeof(WalIndexHdr)) ){
+ /* It is not safe to allow the reader to continue here if frames
+ ** may have been appended to the log before READ_LOCK(0) was obtained.
+ ** When holding READ_LOCK(0), the reader ignores the entire log file,
+ ** which implies that the database file contains a trustworthy
+ ** snapshot. Since holding READ_LOCK(0) prevents a checkpoint from
+ ** happening, this is usually correct.
+ **
+ ** However, if frames have been appended to the log (or if the log
+ ** is wrapped and written for that matter) before the READ_LOCK(0)
+ ** is obtained, that is not necessarily true. A checkpointer may
+ ** have started to backfill the appended frames but crashed before
+ ** it finished. Leaving a corrupt image in the database file.
+ */
+ walUnlockShared(pWal, WAL_READ_LOCK(0));
+ return WAL_RETRY;
+ }
+ pWal->readLock = 0;
+ return SQLITE_OK;
+ }else if( rc!=SQLITE_BUSY ){
+ return rc;
}
- pWal->readLock = 0;
- return SQLITE_OK;
- }else if( rc!=SQLITE_BUSY ){
- return rc;
}
- }
-
- /* If we get this far, it means that the reader will want to use
- ** the WAL to get at content from recent commits. The job now is
- ** to select one of the aReadMark[] entries that is closest to
- ** but not exceeding pWal->hdr.mxFrame and lock that entry.
- */
- mxReadMark = 0;
- mxI = 0;
- mxFrame = pWal->hdr.mxFrame;
+
+ /* If we get this far, it means that the reader will want to use
+ ** the WAL to get at content from recent commits. The job now is
+ ** to select one of the aReadMark[] entries that is closest to
+ ** but not exceeding pWal->hdr.mxFrame and lock that entry.
+ */
+ mxReadMark = 0;
+ mxI = 0;
+ mxFrame = pWal->hdr.mxFrame;
#ifdef SQLITE_ENABLE_SNAPSHOT
- if( pWal->pSnapshot && pWal->pSnapshot->mxFrame<mxFrame ){
- mxFrame = pWal->pSnapshot->mxFrame;
- }
-#endif
- for(i=1; i<WAL_NREADER; i++){
- u32 thisMark = AtomicLoad(pInfo->aReadMark+i); SEH_INJECT_FAULT;
- if( mxReadMark<=thisMark && thisMark<=mxFrame ){
- assert( thisMark!=READMARK_NOT_USED );
- mxReadMark = thisMark;
- mxI = i;
+ if( pWal->pSnapshot && pWal->pSnapshot->mxFrame<mxFrame ){
+ mxFrame = pWal->pSnapshot->mxFrame;
}
- }
- if( (pWal->readOnly & WAL_SHM_RDONLY)==0
- && (mxReadMark<mxFrame || mxI==0)
- ){
+#endif
for(i=1; i<WAL_NREADER; i++){
- rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
- if( rc==SQLITE_OK ){
- AtomicStore(pInfo->aReadMark+i,mxFrame);
- mxReadMark = mxFrame;
+ u32 thisMark = AtomicLoad(pInfo->aReadMark+i); SEH_INJECT_FAULT;
+ if( mxReadMark<=thisMark && thisMark<=mxFrame ){
+ assert( thisMark!=READMARK_NOT_USED );
+ mxReadMark = thisMark;
mxI = i;
- walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
- break;
- }else if( rc!=SQLITE_BUSY ){
- return rc;
}
}
- }
- if( mxI==0 ){
- assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
- return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTINIT;
- }
-
- (void)walEnableBlockingMs(pWal, nBlockTmout);
- rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
- walDisableBlocking(pWal);
- if( rc ){
-#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
- if( rc==SQLITE_BUSY_TIMEOUT ){
- *pCnt |= WAL_RETRY_BLOCKED_MASK;
+ if( (pWal->readOnly & WAL_SHM_RDONLY)==0
+ && (mxReadMark<mxFrame || mxI==0)
+ ){
+ for(i=1; i<WAL_NREADER; i++){
+ rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ if( rc==SQLITE_OK ){
+ AtomicStore(pInfo->aReadMark+i,mxFrame);
+ mxReadMark = mxFrame;
+ mxI = i;
+ walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
+ break;
+ }else if( rc!=SQLITE_BUSY ){
+ return rc;
+ }
+ }
}
+ if( mxI==0 ){
+ assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
+ return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTINIT;
+ }
+
+ (void)walEnableBlockingMs(pWal, nBlockTmout);
+ rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
+ walDisableBlocking(pWal);
+ if( rc ){
+#ifdef SQLITE_ENABLE_SETLK_TIMEOUT
+ if( rc==SQLITE_BUSY_TIMEOUT ){
+ *pCnt |= WAL_RETRY_BLOCKED_MASK;
+ }
#else
- assert( rc!=SQLITE_BUSY_TIMEOUT );
+ assert( rc!=SQLITE_BUSY_TIMEOUT );
#endif
- assert( (rc&0xFF)!=SQLITE_BUSY||rc==SQLITE_BUSY||rc==SQLITE_BUSY_TIMEOUT );
- return (rc&0xFF)==SQLITE_BUSY ? WAL_RETRY : rc;
- }
- /* Now that the read-lock has been obtained, check that neither the
- ** value in the aReadMark[] array or the contents of the wal-index
- ** header have changed.
- **
- ** It is necessary to check that the wal-index header did not change
- ** between the time it was read and when the shared-lock was obtained
- ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility
- ** that the log file may have been wrapped by a writer, or that frames
- ** that occur later in the log than pWal->hdr.mxFrame may have been
- ** copied into the database by a checkpointer. If either of these things
- ** happened, then reading the database with the current value of
- ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
- ** instead.
- **
- ** Before checking that the live wal-index header has not changed
- ** since it was read, set Wal.minFrame to the first frame in the wal
- ** file that has not yet been checkpointed. This client will not need
- ** to read any frames earlier than minFrame from the wal file - they
- ** can be safely read directly from the database file.
- **
- ** Because a ShmBarrier() call is made between taking the copy of
- ** nBackfill and checking that the wal-header in shared-memory still
- ** matches the one cached in pWal->hdr, it is guaranteed that the
- ** checkpointer that set nBackfill was not working with a wal-index
- ** header newer than that cached in pWal->hdr. If it were, that could
- ** cause a problem. The checkpointer could omit to checkpoint
- ** a version of page X that lies before pWal->minFrame (call that version
- ** A) on the basis that there is a newer version (version B) of the same
- ** page later in the wal file. But if version B happens to like past
- ** frame pWal->hdr.mxFrame - then the client would incorrectly assume
- ** that it can read version A from the database file. However, since
- ** we can guarantee that the checkpointer that set nBackfill could not
- ** see any pages past pWal->hdr.mxFrame, this problem does not come up.
- */
- pWal->minFrame = AtomicLoad(&pInfo->nBackfill)+1; SEH_INJECT_FAULT;
- walShmBarrier(pWal);
- if( AtomicLoad(pInfo->aReadMark+mxI)!=mxReadMark
- || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
- ){
- walUnlockShared(pWal, WAL_READ_LOCK(mxI));
- return WAL_RETRY;
- }else{
- assert( mxReadMark<=pWal->hdr.mxFrame );
- pWal->readLock = (i16)mxI;
+ assert((rc&0xFF)!=SQLITE_BUSY||rc==SQLITE_BUSY||rc==SQLITE_BUSY_TIMEOUT);
+ return (rc&0xFF)==SQLITE_BUSY ? WAL_RETRY : rc;
+ }
+ /* Now that the read-lock has been obtained, check that neither the
+ ** value in the aReadMark[] array or the contents of the wal-index
+ ** header have changed.
+ **
+ ** It is necessary to check that the wal-index header did not change
+ ** between the time it was read and when the shared-lock was obtained
+ ** on WAL_READ_LOCK(mxI) was obtained to account for the possibility
+ ** that the log file may have been wrapped by a writer, or that frames
+ ** that occur later in the log than pWal->hdr.mxFrame may have been
+ ** copied into the database by a checkpointer. If either of these things
+ ** happened, then reading the database with the current value of
+ ** pWal->hdr.mxFrame risks reading a corrupted snapshot. So, retry
+ ** instead.
+ **
+ ** Before checking that the live wal-index header has not changed
+ ** since it was read, set Wal.minFrame to the first frame in the wal
+ ** file that has not yet been checkpointed. This client will not need
+ ** to read any frames earlier than minFrame from the wal file - they
+ ** can be safely read directly from the database file.
+ **
+ ** Because a ShmBarrier() call is made between taking the copy of
+ ** nBackfill and checking that the wal-header in shared-memory still
+ ** matches the one cached in pWal->hdr, it is guaranteed that the
+ ** checkpointer that set nBackfill was not working with a wal-index
+ ** header newer than that cached in pWal->hdr. If it were, that could
+ ** cause a problem. The checkpointer could omit to checkpoint
+ ** a version of page X that lies before pWal->minFrame (call that version
+ ** A) on the basis that there is a newer version (version B) of the same
+ ** page later in the wal file. But if version B happens to like past
+ ** frame pWal->hdr.mxFrame - then the client would incorrectly assume
+ ** that it can read version A from the database file. However, since
+ ** we can guarantee that the checkpointer that set nBackfill could not
+ ** see any pages past pWal->hdr.mxFrame, this problem does not come up.
+ */
+ pWal->minFrame = AtomicLoad(&pInfo->nBackfill)+1; SEH_INJECT_FAULT;
+ walShmBarrier(pWal);
+ if( AtomicLoad(pInfo->aReadMark+mxI)!=mxReadMark
+ || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
+ ){
+ walUnlockShared(pWal, WAL_READ_LOCK(mxI));
+ return WAL_RETRY;
+ }else{
+ assert( mxReadMark<=pWal->hdr.mxFrame );
+ pWal->readLock = (i16)mxI;
+ }
}
return rc;
}
@@ -3467,8 +3484,11 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
** read-lock.
*/
void sqlite3WalEndReadTransaction(Wal *pWal){
- sqlite3WalEndWriteTransaction(pWal);
+#ifndef SQLITE_ENABLE_SETLK_TIMEOUT
+ assert( pWal->writeLock==0 || pWal->readLock<0 );
+#endif
if( pWal->readLock>=0 ){
+ sqlite3WalEndWriteTransaction(pWal);
walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
pWal->readLock = -1;
}
@@ -3661,7 +3681,7 @@ int sqlite3WalBeginWriteTransaction(Wal *pWal){
** read-transaction was even opened, making this call a no-op.
** Return early. */
if( pWal->writeLock ){
- assert( !memcmp(&pWal->hdr,(void *)walIndexHdr(pWal),sizeof(WalIndexHdr)) );
+ assert( !memcmp(&pWal->hdr,(void*)pWal->apWiData[0],sizeof(WalIndexHdr)) );
return SQLITE_OK;
}
#endif
@@ -3736,12 +3756,12 @@ int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
SEH_TRY {
/* Restore the clients cache of the wal-index header to the state it
- ** was in before the client began writing to the database.
+ ** was in before the client began writing to the database.
*/
memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr));
-
- for(iFrame=pWal->hdr.mxFrame+1;
- ALWAYS(rc==SQLITE_OK) && iFrame<=iMax;
+
+ for(iFrame=pWal->hdr.mxFrame+1;
+ ALWAYS(rc==SQLITE_OK) && iFrame<=iMax;
iFrame++
){
/* This call cannot fail. Unless the page for which the page number
@@ -3761,6 +3781,7 @@ int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
if( iMax!=pWal->hdr.mxFrame ) walCleanupHash(pWal);
}
SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+ pWal->iReCksum = 0;
}
return rc;
}
@@ -3808,6 +3829,9 @@ int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
walCleanupHash(pWal);
}
SEH_EXCEPT( rc = SQLITE_IOERR_IN_PAGE; )
+ if( pWal->iReCksum>pWal->hdr.mxFrame ){
+ pWal->iReCksum = 0;
+ }
}
return rc;
@@ -4497,7 +4521,20 @@ void sqlite3WalSnapshotOpen(
Wal *pWal,
sqlite3_snapshot *pSnapshot
){
- pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
+ if( pSnapshot && ((WalIndexHdr*)pSnapshot)->iVersion==0 ){
+ /* iVersion==0 means that this is a call to sqlite3_snapshot_get(). In
+ ** this case set the bGetSnapshot flag so that if the call to
+ ** sqlite3_snapshot_get() is about to read transaction on this wal
+ ** file, it does not take read-lock 0 if the wal file has been completely
+ ** checkpointed. Taking read-lock 0 would work, but then it would be
+ ** possible for a subsequent writer to destroy the snapshot even while
+ ** this connection is holding its read-transaction open. This is contrary
+ ** to user expectations, so we avoid it by not taking read-lock 0. */
+ pWal->bGetSnapshot = 1;
+ }else{
+ pWal->pSnapshot = (WalIndexHdr*)pSnapshot;
+ pWal->bGetSnapshot = 0;
+ }
}
/*
generated by cgit v1.2.3 (git 2.25.1) at 2025-07-19 05:16:26 +0000