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Shift the meaning of aReadMark[] back so that +1 offset from mxFrame is

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removed.  Add the new READMARK_NOT_USED value (0xffffffff) instead of
zero to signal an aReadMark[] that is not in use.

FossilOrigin-Name: c576827d55c156572b76cf7063e9f253ca6e7403
This commit is contained in:
drh
2010-06-09 14:45:12 +00:00
parent 15651f61df
commit db7f647e41
4 changed files with 42 additions and 21 deletions
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34
src/wal.c
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@@ -285,9 +285,12 @@ struct WalIndexHdr {
**
** There is one entry in aReadMark[] for each reader lock. If a reader
** holds read-lock K, then the value in aReadMark[K] is no greater than
** the mxFrame for that reader. aReadMark[0] is a special case. It
** always holds zero. Readers holding WAL_READ_LOCK(0) always ignore
** the entire WAL and read all content directly from the database.
** the mxFrame for that reader. The value READMARK_NOT_USED (0xffffffff)
** for any aReadMark[] means that entry is unused. aReadMark[0] is
** a special case; its value is never used and it exists as a place-holder
** to avoid having to offset aReadMark[] indexs by one. Readers holding
** WAL_READ_LOCK(0) always ignore the entire WAL and read all content
** directly from the database.
**
** The value of aReadMark[K] may only be changed by a thread that
** is holding an exclusive lock on WAL_READ_LOCK(K). Thus, the value of
@@ -320,6 +323,7 @@ struct WalCkptInfo {
u32 nBackfill; /* Number of WAL frames backfilled into DB */
u32 aReadMark[WAL_NREADER]; /* Reader marks */
};
#define READMARK_NOT_USED 0xffffffff
/* A block of WALINDEX_LOCK_RESERVED bytes beginning at
@@ -1076,15 +1080,20 @@ finished:
rc = walIndexRemap(pWal, walMappingSize(1));
}
if( rc==SQLITE_OK ){
volatile WalCkptInfo *pInfo;
int i;
pWal->hdr.aFrameCksum[0] = aFrameCksum[0];
pWal->hdr.aFrameCksum[1] = aFrameCksum[1];
walIndexWriteHdr(pWal);
/* Zero the checkpoint-header. This is safe because this thread is
/* Reset the checkpoint-header. This is safe because this thread is
** currently holding locks that exclude all other readers, writers and
** checkpointers.
*/
memset((void *)walCkptInfo(pWal), 0, sizeof(WalCkptInfo));
pInfo = walCkptInfo(pWal);
pInfo->nBackfill = 0;
pInfo->aReadMark[0] = 0;
for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;
}
recovery_error:
@@ -1426,14 +1435,14 @@ static int walCheckpoint(
assert( pInfo==walCkptInfo(pWal) );
for(i=1; i<WAL_NREADER; i++){
u32 y = pInfo->aReadMark[i];
if( y>0 && mxSafeFrame>=y ){
if( mxSafeFrame>=y ){
assert( y<=pWal->hdr.mxFrame );
rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
if( rc==SQLITE_OK ){
pInfo->aReadMark[i] = 0;
pInfo->aReadMark[i] = READMARK_NOT_USED;
walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
}else if( rc==SQLITE_BUSY ){
mxSafeFrame = y-1;
mxSafeFrame = y;
}else{
goto walcheckpoint_out;
}
@@ -1780,7 +1789,8 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
mxI = 0;
for(i=1; i<WAL_NREADER; i++){
u32 thisMark = pInfo->aReadMark[i];
if( mxReadMark<thisMark && thisMark<=(pWal->hdr.mxFrame+1) ){
if( mxReadMark<=thisMark && thisMark<=pWal->hdr.mxFrame ){
assert( thisMark!=READMARK_NOT_USED );
mxReadMark = thisMark;
mxI = i;
}
@@ -1792,7 +1802,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
*/
rc = walLockExclusive(pWal, WAL_READ_LOCK(1), 1);
if( rc==SQLITE_OK ){
pInfo->aReadMark[1] = pWal->hdr.mxFrame+1;
pInfo->aReadMark[1] = pWal->hdr.mxFrame;
walUnlockExclusive(pWal, WAL_READ_LOCK(1), 1);
rc = WAL_RETRY;
}else if( rc==SQLITE_BUSY ){
@@ -1804,7 +1814,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
for(i=1; i<WAL_NREADER; i++){
rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
if( rc==SQLITE_OK ){
mxReadMark = pInfo->aReadMark[i] = pWal->hdr.mxFrame+1;
mxReadMark = pInfo->aReadMark[i] = pWal->hdr.mxFrame;
mxI = i;
walUnlockExclusive(pWal, WAL_READ_LOCK(i), 1);
break;
@@ -1845,7 +1855,7 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
walUnlockShared(pWal, WAL_READ_LOCK(mxI));
return WAL_RETRY;
}else{
assert( mxReadMark<=(pWal->hdr.mxFrame+1) );
assert( mxReadMark<=pWal->hdr.mxFrame );
pWal->readLock = mxI;
}
}