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If it is known that checksums will be recalculated on transaction commit, skip calculating checksums when appending frames to the wal file. When recalculating checksums, recalculate them starting with the first overwritten frame - not the first frame in the transaction.

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FossilOrigin-Name: 16b34f2537bbc7846d8e6dc2b35daae5af241c1b
This commit is contained in:
dan
2016-01-09 18:57:35 +00:00
parent d6f7c97952
commit c9a9022b21
3 changed files with 42 additions and 46 deletions
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71
src/wal.c
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@@ -445,6 +445,7 @@ struct Wal {
u8 padToSectorBoundary; /* Pad transactions out to the next sector */
WalIndexHdr hdr; /* Wal-index header for current transaction */
u32 minFrame; /* Ignore wal frames before this one */
u32 iReCksum; /* On commit, recalculate checksums from here */
const char *zWalName; /* Name of WAL file */
u32 nCkpt; /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
@@ -462,13 +463,6 @@ struct Wal {
#define WAL_EXCLUSIVE_MODE 1
#define WAL_HEAPMEMORY_MODE 2
/*
** Values for Wal.writeLock.
*/
#define WAL_WRITELOCK_UNLOCKED 0
#define WAL_WRITELOCK_LOCKED 1
#define WAL_WRITELOCK_RECKSUM 2
/*
** Possible values for WAL.readOnly
*/
@@ -705,14 +699,16 @@ static void walEncodeFrame(
assert( WAL_FRAME_HDRSIZE==24 );
sqlite3Put4byte(&aFrame[0], iPage);
sqlite3Put4byte(&aFrame[4], nTruncate);
memcpy(&aFrame[8], pWal->hdr.aSalt, 8);
if( pWal->iReCksum==0 ){
memcpy(&aFrame[8], pWal->hdr.aSalt, 8);
nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
nativeCksum = (pWal->hdr.bigEndCksum==SQLITE_BIGENDIAN);
walChecksumBytes(nativeCksum, aFrame, 8, aCksum, aCksum);
walChecksumBytes(nativeCksum, aData, pWal->szPage, aCksum, aCksum);
sqlite3Put4byte(&aFrame[16], aCksum[0]);
sqlite3Put4byte(&aFrame[20], aCksum[1]);
sqlite3Put4byte(&aFrame[16], aCksum[0]);
sqlite3Put4byte(&aFrame[20], aCksum[1]);
}
}
/*
@@ -2639,6 +2635,7 @@ int sqlite3WalBeginWriteTransaction(Wal *pWal){
/* Cannot start a write transaction without first holding a read
** transaction. */
assert( pWal->readLock>=0 );
assert( pWal->writeLock==0 && pWal->iReCksum==0 );
if( pWal->readOnly ){
return SQLITE_READONLY;
@@ -2674,6 +2671,7 @@ int sqlite3WalEndWriteTransaction(Wal *pWal){
if( pWal->writeLock ){
walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
pWal->writeLock = 0;
pWal->iReCksum = 0;
pWal->truncateOnCommit = 0;
}
return SQLITE_OK;
@@ -2895,41 +2893,40 @@ static int walWriteOneFrame(
/*
** This function is called as part of committing a transaction within which
** one or more frames have been overwritten. It updates the checksums for
** all frames written to the wal file by the current transaction.
**
** Argument pLive is a pointer to the first wal-index header in shared
** memory (the copy readers will see if they open a read-transaction now,
** before the current commit is finished). This is safe to use because the
** caller holds the WRITER lock. The first frame to update the checksum
** for is (pLive->mxFrame+1). The last is argument iLast.
** all frames written to the wal file by the current transaction starting
** with the earliest to have been overwritten.
**
** SQLITE_OK is returned if successful, or an SQLite error code otherwise.
*/
static int walRewriteChecksums(Wal *pWal, WalIndexHdr *pLive, u32 iLast){
static int walRewriteChecksums(Wal *pWal, u32 iLast){
const int szPage = pWal->szPage;/* Database page size */
int rc = SQLITE_OK; /* Return code */
u8 *aBuf; /* Buffer to load data from wal file into */
u8 aFrame[WAL_FRAME_HDRSIZE]; /* Buffer to assemble frame-headers in */
u32 iRead; /* Next frame to read from wal file */
i64 iCksumOff;
aBuf = sqlite3_malloc(szPage + WAL_FRAME_HDRSIZE);
if( aBuf==0 ) return SQLITE_NOMEM;
/* Find the checksum values to use as input for the checksum of the
** first frame written by this transaction. If that frame is frame 1
** (implying that the current transaction restarted the wal file),
** these values must be read from the wal-file header. If the first
** frame to update the checksum of is not frame 1, then the initial
** checksum values can be copied from pLive. */
if( pLive->mxFrame==0 ){
rc = sqlite3OsRead(pWal->pWalFd, aBuf, sizeof(u32)*2, 24);
pWal->hdr.aFrameCksum[0] = sqlite3Get4byte(aBuf);
pWal->hdr.aFrameCksum[1] = sqlite3Get4byte(&aBuf[sizeof(u32)]);
/* Find the checksum values to use as input for the recalculating the
** first checksum. If the first frame is frame 1 (implying that the current
** transaction restarted the wal file), these values must be read from the
** wal-file header. Otherwise, read them from the frame header of the
** previous frame. */
assert( pWal->iReCksum>0 );
if( pWal->iReCksum==1 ){
iCksumOff = 24;
}else{
memcpy(pWal->hdr.aFrameCksum, pLive->aFrameCksum, sizeof(u32)*2);
iCksumOff = walFrameOffset(pWal->iReCksum-1, szPage) + 16;
}
rc = sqlite3OsRead(pWal->pWalFd, aBuf, sizeof(u32)*2, iCksumOff);
pWal->hdr.aFrameCksum[0] = sqlite3Get4byte(aBuf);
pWal->hdr.aFrameCksum[1] = sqlite3Get4byte(&aBuf[sizeof(u32)]);
for(iRead=pLive->mxFrame+1; rc==SQLITE_OK && iRead<=iLast; iRead++){
iRead = pWal->iReCksum;
pWal->iReCksum = 0;
for(; rc==SQLITE_OK && iRead<=iLast; iRead++){
i64 iOff = walFrameOffset(iRead, szPage);
rc = sqlite3OsRead(pWal->pWalFd, aBuf, szPage+WAL_FRAME_HDRSIZE, iOff);
if( rc==SQLITE_OK ){
@@ -3065,7 +3062,9 @@ int sqlite3WalFrames(
if( rc ) return rc;
if( iWrite>=iFirst ){
i64 iOff = walFrameOffset(iWrite, szPage) + WAL_FRAME_HDRSIZE;
pWal->writeLock = WAL_WRITELOCK_RECKSUM;
if( pWal->iReCksum==0 || iWrite<pWal->iReCksum ){
pWal->iReCksum = iWrite;
}
rc = sqlite3OsWrite(pWal->pWalFd, p->pData, szPage, iOff);
if( rc ) return rc;
p->flags &= ~PGHDR_WAL_APPEND;
@@ -3084,8 +3083,8 @@ int sqlite3WalFrames(
}
/* Recalculate checksums within the wal file if required. */
if( isCommit && pWal->writeLock==WAL_WRITELOCK_RECKSUM ){
rc = walRewriteChecksums(pWal, pLive, iFrame);
if( isCommit && pWal->iReCksum ){
rc = walRewriteChecksums(pWal, iFrame);
if( rc ) return rc;
}