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Changes to make WAL more robust against SHM locking failures and OOM errors.

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FossilOrigin-Name: ebf4041383c3cdddb5861960359abd209d4a1028
This commit is contained in:
drh
2010-06-02 14:45:51 +00:00
parent 048129dcb9
commit aab4c02e47
5 changed files with 47 additions and 26 deletions
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40
src/wal.c
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@@ -377,6 +377,9 @@ struct Wal {
WalIndexHdr hdr; /* Wal-index header for current transaction */
char *zWalName; /* Name of WAL file */
u32 nCkpt; /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
u8 lockError; /* True if a locking error has occurred */
#endif
};
/*
@@ -629,6 +632,7 @@ static int walLockShared(Wal *pWal, int lockIdx){
SQLITE_SHM_LOCK | SQLITE_SHM_SHARED);
WALTRACE(("WAL%p: acquire SHARED-%s %s\n", pWal,
walLockName(lockIdx), rc ? "failed" : "ok"));
VVA_ONLY( pWal->lockError = (rc!=SQLITE_OK && rc!=SQLITE_BUSY); )
return rc;
}
static void walUnlockShared(Wal *pWal, int lockIdx){
@@ -644,6 +648,7 @@ static int walLockExclusive(Wal *pWal, int lockIdx, int n){
SQLITE_SHM_LOCK | SQLITE_SHM_EXCLUSIVE);
WALTRACE(("WAL%p: acquire EXCLUSIVE-%s cnt=%d %s\n", pWal,
walLockName(lockIdx), n, rc ? "failed" : "ok"));
VVA_ONLY( pWal->lockError = (rc!=SQLITE_OK && rc!=SQLITE_BUSY); )
return rc;
}
static void walUnlockExclusive(Wal *pWal, int lockIdx, int n){
@@ -1693,7 +1698,7 @@ static int walIndexReadHdr(Wal *pWal, int *pChanged){
** so it takes care to hold an exclusive lock on the corresponding
** WAL_READ_LOCK() while changing values.
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal){
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
volatile WalIndexHdr *pHdr; /* Header of the wal-index */
volatile WalCkptInfo *pInfo; /* Checkpoint information in wal-index */
u32 mxReadMark; /* Largest aReadMark[] value */
@@ -1703,6 +1708,12 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal){
assert( pWal->readLock<0 ); /* Not currently locked */
/* Take steps to avoid spinning forever if there is a protocol error. */
if( cnt>5 ){
if( cnt>100 ) return SQLITE_PROTOCOL;
sqlite3OsSleep(pWal->pVfs, 1);
}
if( !useWal ){
rc = walIndexReadHdr(pWal, pChanged);
if( rc==SQLITE_BUSY ){
@@ -1820,9 +1831,10 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal){
*/
int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
int rc; /* Return code */
int cnt = 0; /* Number of TryBeginRead attempts */
do{
rc = walTryBeginRead(pWal, pChanged, 0);
rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
}while( rc==WAL_RETRY );
walIndexUnmap(pWal);
return rc;
@@ -1859,8 +1871,8 @@ int sqlite3WalRead(
u32 iLast = pWal->hdr.mxFrame; /* Last page in WAL for this reader */
int iHash; /* Used to loop through N hash tables */
/* This routine is only called from within a read transaction */
assert( pWal->readLock>=0 );
/* This routine is only be called from within a read transaction. */
assert( pWal->readLock>=0 || pWal->lockError );
/* If the "last page" field of the wal-index header snapshot is 0, then
** no data will be read from the wal under any circumstances. Return early
@@ -1982,7 +1994,7 @@ int sqlite3WalRead(
** Set *pPgno to the size of the database file (or zero, if unknown).
*/
void sqlite3WalDbsize(Wal *pWal, Pgno *pPgno){
assert( pWal->readLock>=0 );
assert( pWal->readLock>=0 || pWal->lockError );
*pPgno = pWal->hdr.nPage;
}
@@ -2133,6 +2145,8 @@ int sqlite3WalSavepointUndo(Wal *pWal, u32 *aWalData){
*/
static int walRestartLog(Wal *pWal){
int rc = SQLITE_OK;
int cnt;
if( pWal->readLock==0
&& SQLITE_OK==(rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame)))
){
@@ -2163,9 +2177,10 @@ static int walRestartLog(Wal *pWal){
}
walUnlockShared(pWal, WAL_READ_LOCK(0));
pWal->readLock = -1;
cnt = 0;
do{
int notUsed;
rc = walTryBeginRead(pWal, &notUsed, 1);
rc = walTryBeginRead(pWal, &notUsed, 1, ++cnt);
}while( rc==WAL_RETRY );
/* Unmap the wal-index before returning. Otherwise the VFS layer may
@@ -2418,22 +2433,25 @@ int sqlite3WalCallback(Wal *pWal){
*/
int sqlite3WalExclusiveMode(Wal *pWal, int op){
int rc;
assert( pWal->writeLock==0 && pWal->readLock>=0 );
assert( pWal->writeLock==0 );
/* pWal->readLock is usually set, but might be -1 if there was a prior OOM */
assert( pWal->readLock>=0 || pWal->lockError );
if( op==0 ){
if( pWal->exclusiveMode ){
pWal->exclusiveMode = 0;
if( walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK ){
if( pWal->readLock>=0
&& walLockShared(pWal, WAL_READ_LOCK(pWal->readLock))!=SQLITE_OK
){
pWal->exclusiveMode = 1;
}
rc = pWal->exclusiveMode==0;
}else{
/* No changes. Either already in locking_mode=NORMAL or else the
** acquisition of the read-lock failed. The pager must continue to
** hold the database exclusive lock. */
/* Already in locking_mode=NORMAL */
rc = 0;
}
}else if( op>0 ){
assert( pWal->exclusiveMode==0 );
assert( pWal->readLock>=0 );
walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
pWal->exclusiveMode = 1;
rc = 1;