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If SQLITE_ENABLE_WAL2NOCKSUM is defined, then SQLite calculates the frame checksums used in wal2 mode based on the previous checksum and the frame header only, not the frame body only. This risks corruption following a OS crash or power failure, but also speeds up writes in wal2 mode.

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FossilOrigin-Name: dc74bd8915a9e1a915fb4ff3229a7b5e8f89486fe1df812a7738f6627d379648
This commit is contained in:
dan
2025-01-29 15:11:07 +00:00
parent 2ce43ceec1
commit 2a8768ad66
6 changed files with 67 additions and 20 deletions
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35
src/wal.c
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@@ -461,6 +461,17 @@ int sqlite3WalTrace = 0;
#define WAL_VERSION1 3007000 /* For "journal_mode=wal" */
#define WAL_VERSION2 3021000 /* For "journal_mode=wal2" */
#ifdef SQLITE_ENABLE_WAL2NOCKSUM
# undef WAL_VERSION2
# define WAL_VERSION2 3048000 /* For "journal_mode=wal2" sans checksums */
# define isNocksum(pWal) isWalMode2(pWal)
#else
# define isNocksum(pWal) 0
#endif
/*
** Index numbers for various locking bytes. WAL_NREADER is the number
@@ -1240,10 +1251,13 @@ static void walEncodeFrame(
nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
if( isNocksum(pWal)==0 ){
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
}
sqlite3Put4byte(&aFrame[16], aCksum[0]);
sqlite3Put4byte(&aFrame[20], aCksum[1]);
}else{
memset(&aFrame[8], 0, 16);
}
@@ -1287,7 +1301,9 @@ static int walDecodeFrame(
*/
nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
if( isNocksum(pWal)==0 ){
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
}
if( aCksum[0]!=sqlite3Get4byte(&aFrame[16])
|| aCksum[1]!=sqlite3Get4byte(&aFrame[20])
){
@@ -5110,10 +5126,21 @@ static int walWriteOneFrame(
pData = pPage->pData;
walEncodeFrame(p->pWal, pPage->pgno, nTruncate, pData, aFrame);
rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset);
if( rc ) return rc;
if( isNocksum(p->pWal)==0 ){
/* Write the header in normal mode */
rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset);
if( rc ) return rc;
}
/* Write the page data */
rc = walWriteToLog(p, pData, p->szPage, iOffset+sizeof(aFrame));
if( isNocksum(p->pWal) ){
/* Write the header in no-checksum mode */
if( rc ) return rc;
rc = walWriteToLog(p, aFrame, sizeof(aFrame), iOffset);
}
return rc;
}