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If a readonly_shm connection cannot map the *-shm file because no other

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process is holding the DMS lock, have it read from the database file only,
ignoring any content in the wal file.

FossilOrigin-Name: ce5d13c2de69b73378637d4f7e109714f7cd17bf1d1ad995e0be442d517ed1b3
This commit is contained in:
dan
2017-11-01 20:59:28 +00:00
parent 514c4b7e5d
commit 92c02da33e
5 changed files with 183 additions and 59 deletions
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24
src/wal.c
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@@ -575,9 +575,11 @@ static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ,
pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
);
if( rc==SQLITE_READONLY ){
if( (rc&0xff)==SQLITE_READONLY ){
pWal->readOnly |= WAL_SHM_RDONLY;
rc = SQLITE_OK;
if( rc==SQLITE_READONLY ){
rc = SQLITE_OK;
}
}
}
}
@@ -2084,6 +2086,14 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){
assert( pChanged );
rc = walIndexPage(pWal, 0, &page0);
if( rc!=SQLITE_OK ){
if( rc==SQLITE_READONLY_CANTLOCK
#ifdef SQLITE_ENABLE_SNAPSHOT
&& pWal->pSnapshot==0
#endif
){
memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
rc = SQLITE_OK;
}
return rc;
};
assert( page0 || pWal->writeLock==0 );
@@ -2259,8 +2269,10 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
}
}
pInfo = walCkptInfo(pWal);
if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame
assert( pWal->nWiData>0 );
assert( pWal->apWiData[0] || (pWal->readOnly & WAL_SHM_RDONLY) );
pInfo = pWal->apWiData[0] ? walCkptInfo(pWal) : 0;
if( !useWal && (pInfo==0 || pInfo->nBackfill==pWal->hdr.mxFrame)
#ifdef SQLITE_ENABLE_SNAPSHOT
&& (pWal->pSnapshot==0 || pWal->hdr.mxFrame==0
|| 0==memcmp(&pWal->hdr, pWal->pSnapshot, sizeof(WalIndexHdr)))
@@ -2272,7 +2284,9 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
rc = walLockShared(pWal, WAL_READ_LOCK(0));
walShmBarrier(pWal);
if( rc==SQLITE_OK ){
if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
if( pInfo
&& 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,