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Proposed changes that ensure that the WAL header is written prior to the

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first commit mark.

FossilOrigin-Name: 91d0437c0702904d27f0ef7b1b52d0797efe1826
This commit is contained in:
drh
2011-12-16 19:34:36 +00:00
parent eed4250598
commit 88f975a7a4
3 changed files with 53 additions and 11 deletions
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47
src/wal.c
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@@ -414,6 +414,7 @@ struct Wal {
u32 iCallback; /* Value to pass to log callback (or 0) */
i64 mxWalSize; /* Truncate WAL to this size upon reset */
int nWiData; /* Size of array apWiData */
int szFirstBlock; /* Size of first block written to WAL file */
volatile u32 **apWiData; /* Pointer to wal-index content in memory */
u32 szPage; /* Database page size */
i16 readLock; /* Which read lock is being held. -1 for none */
@@ -2617,6 +2618,40 @@ static int walRestartLog(Wal *pWal){
return rc;
}
/*
** Write iAmt bytes of content into the WAL file beginning at iOffset.
**
** When crossing the boundary between the first and second sectors of the
** file, first write all of the first sector content, then fsync(), then
** continue writing content for the second sector. This ensures that
** the WAL header is overwritten before the first commit mark.
*/
static int walWriteToLog(
Wal *pWal, /* WAL to write to */
void *pContent, /* Content to be written */
int iAmt, /* Number of bytes to write */
sqlite3_int64 iOffset /* Start writing at this offset */
){
int rc;
if( iOffset>=pWal->szFirstBlock || iOffset+iAmt<pWal->szFirstBlock ){
/* The common and fast case. Just write the data. */
rc = sqlite3OsWrite(pWal->pWalFd, pContent, iAmt, iOffset);
}else{
/* If this write will cross the first sector boundary, it has to
** be split it two with a sync in between. */
int iFirstAmt = pWal->szFirstBlock - iOffset;
assert( iFirstAmt>0 && iFirstAmt<iAmt );
rc = sqlite3OsWrite(pWal->pWalFd, pContent, iFirstAmt, iOffset);
if( rc ) return rc;
rc = sqlite3OsSync(pWal->pWalFd, SQLITE_SYNC_NORMAL);
if( rc ) return rc;
pContent = (void*)(iFirstAmt + (char*)pContent);
rc = sqlite3OsWrite(pWal->pWalFd, pContent,
iAmt-iFirstAmt, iOffset+iFirstAmt);
}
return rc;
}
/*
** Write a set of frames to the log. The caller must hold the write-lock
** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
@@ -2686,6 +2721,10 @@ int sqlite3WalFrames(
}
assert( (int)pWal->szPage==szPage );
/* The size of the block containing the WAL header */
pWal->szFirstBlock = sqlite3OsSectorSize(pWal->pWalFd);
if( szPage>pWal->szFirstBlock ) pWal->szFirstBlock = szPage;
/* Write the log file. */
for(p=pList; p; p=p->pDirty){
u32 nDbsize; /* Db-size field for frame header */
@@ -2703,13 +2742,13 @@ int sqlite3WalFrames(
pData = p->pData;
#endif
walEncodeFrame(pWal, p->pgno, nDbsize, pData, aFrame);
rc = sqlite3OsWrite(pWal->pWalFd, aFrame, sizeof(aFrame), iOffset);
rc = walWriteToLog(pWal, aFrame, sizeof(aFrame), iOffset);
if( rc!=SQLITE_OK ){
return rc;
}
/* Write the page data */
rc = sqlite3OsWrite(pWal->pWalFd, pData, szPage, iOffset+sizeof(aFrame));
rc = walWriteToLog(pWal, pData, szPage, iOffset+sizeof(aFrame));
if( rc!=SQLITE_OK ){
return rc;
}
@@ -2734,12 +2773,12 @@ int sqlite3WalFrames(
#endif
walEncodeFrame(pWal, pLast->pgno, nTruncate, pData, aFrame);
/* testcase( IS_BIG_INT(iOffset) ); // requires a 4GiB WAL */
rc = sqlite3OsWrite(pWal->pWalFd, aFrame, sizeof(aFrame), iOffset);
rc = walWriteToLog(pWal, aFrame, sizeof(aFrame), iOffset);
if( rc!=SQLITE_OK ){
return rc;
}
iOffset += WAL_FRAME_HDRSIZE;
rc = sqlite3OsWrite(pWal->pWalFd, pData, szPage, iOffset);
rc = walWriteToLog(pWal, pData, szPage, iOffset);
if( rc!=SQLITE_OK ){
return rc;
}