i64 iStart;                     /* Start of region in log file */
  i64 iEnd;                       /* End of region in log file */
};

struct DbLog {
  u32 cksum0;                     /* Checksum 0 at offset iOff */
  u32 cksum1;                     /* Checksum 1 at offset iOff */

  LogRegion aRegion[3];           /* Log file regions (see docs in lsm_log.c) */
};

/*
** Tree header structure. 
*/
struct TreeHeader {
................................................................................
int lsmCheckpointPgsz(u32 *);
int lsmCheckpointBlksz(u32 *);
void lsmCheckpointLogoffset(u32 *aCkpt, DbLog *pLog);
void lsmCheckpointZeroLogoffset(lsm_db *);

int lsmCheckpointSaveWorker(lsm_db *pDb, int, int);
int lsmDatabaseFull(lsm_db *pDb);
int lsmCheckpointSynced(lsm_db *pDb, i64 *piId);


/* 
** Functions from file "lsm_tree.c".
*/
int lsmTreeNew(lsm_env *, int (*)(void *, int, void *, int), Tree **ppTree);
void lsmTreeRelease(lsm_env *, Tree *);
................................................................................
int lsmLogWrite(lsm_db *, void *, int, void *, int);
int lsmLogCommit(lsm_db *);
void lsmLogEnd(lsm_db *pDb, int bCommit);
void lsmLogTell(lsm_db *, LogMark *);
void lsmLogSeek(lsm_db *, LogMark *);

int lsmLogRecover(lsm_db *);
void lsmLogCheckpoint(lsm_db *, lsm_i64);
int lsmLogStructure(lsm_db *pDb, char **pzVal);


/**************************************************************************
** Functions from file "lsm_shared.c".
*/

  i64 iStart;                     /* Start of region in log file */
  i64 iEnd;                       /* End of region in log file */
};

struct DbLog {
  u32 cksum0;                     /* Checksum 0 at offset iOff */
  u32 cksum1;                     /* Checksum 1 at offset iOff */
  i64 iSnapshotId;                /* Log space has been reclaimed to this ss */
  LogRegion aRegion[3];           /* Log file regions (see docs in lsm_log.c) */
};

/*
** Tree header structure. 
*/
struct TreeHeader {
................................................................................
int lsmCheckpointPgsz(u32 *);
int lsmCheckpointBlksz(u32 *);
void lsmCheckpointLogoffset(u32 *aCkpt, DbLog *pLog);
void lsmCheckpointZeroLogoffset(lsm_db *);

int lsmCheckpointSaveWorker(lsm_db *pDb, int, int);
int lsmDatabaseFull(lsm_db *pDb);
int lsmCheckpointSynced(lsm_db *pDb, i64 *piId, i64 *piLog);


/* 
** Functions from file "lsm_tree.c".
*/
int lsmTreeNew(lsm_env *, int (*)(void *, int, void *, int), Tree **ppTree);
void lsmTreeRelease(lsm_env *, Tree *);
................................................................................
int lsmLogWrite(lsm_db *, void *, int, void *, int);
int lsmLogCommit(lsm_db *);
void lsmLogEnd(lsm_db *pDb, int bCommit);
void lsmLogTell(lsm_db *, LogMark *);
void lsmLogSeek(lsm_db *, LogMark *);

int lsmLogRecover(lsm_db *);

int lsmLogStructure(lsm_db *pDb, char **pzVal);


/**************************************************************************
** Functions from file "lsm_shared.c".
*/

**
** If successful, this function loads the snapshot from the meta-page, 
** verifies its checksum and sets *piId to the snapshot-id before returning
** LSM_OK. Or, if the checksum attempt fails, *piId is set to zero and
** LSM_OK returned. If an error occurs, an LSM error code is returned and
** the final value of *piId is undefined.
*/
int lsmCheckpointSynced(lsm_db *pDb, i64 *piId){
  int rc = LSM_OK;
  MetaPage *pPg;
  u32 iMeta;

  iMeta = pDb->pShmhdr->iMetaPage;
  rc = lsmFsMetaPageGet(pDb->pFS, 0, iMeta, &pPg);
  if( rc==LSM_OK ){
................................................................................
    if( nCkpt<(LSM_META_PAGE_SIZE/sizeof(u32)) ){
      u32 *aCopy = lsmMallocRc(pDb->pEnv, sizeof(u32) * nCkpt, &rc);
      if( aCopy ){
        memcpy(aCopy, aData, nCkpt*sizeof(u32));
        ckptChangeEndianness(aCopy, nCkpt);
        if( ckptChecksumOk(aCopy) ){
          *piId = lsmCheckpointId(aCopy, 0);

        }
        lsmFree(pDb->pEnv, aCopy);
      }
    }
    lsmFsMetaPageRelease(pPg);
  }

................................................................................
  DbLog *pLog
){ 
  u32 iOffMSB = aCkpt[CKPT_HDR_LO_MSW];
  u32 iOffLSB = aCkpt[CKPT_HDR_LO_LSW];
  pLog->aRegion[2].iStart = (((i64)iOffMSB) << 32) + ((i64)iOffLSB);
  pLog->cksum0 = aCkpt[CKPT_HDR_LO_CKSUM1];
  pLog->cksum1 = aCkpt[CKPT_HDR_LO_CKSUM2];

}

void lsmCheckpointZeroLogoffset(lsm_db *pDb){
  u32 nCkpt;

  nCkpt = pDb->aSnapshot[CKPT_HDR_NCKPT];
  assert( nCkpt>CKPT_HDR_NCKPT );

**
** If successful, this function loads the snapshot from the meta-page, 
** verifies its checksum and sets *piId to the snapshot-id before returning
** LSM_OK. Or, if the checksum attempt fails, *piId is set to zero and
** LSM_OK returned. If an error occurs, an LSM error code is returned and
** the final value of *piId is undefined.
*/
int lsmCheckpointSynced(lsm_db *pDb, i64 *piId, i64 *piLog){
  int rc = LSM_OK;
  MetaPage *pPg;
  u32 iMeta;

  iMeta = pDb->pShmhdr->iMetaPage;
  rc = lsmFsMetaPageGet(pDb->pFS, 0, iMeta, &pPg);
  if( rc==LSM_OK ){
................................................................................
    if( nCkpt<(LSM_META_PAGE_SIZE/sizeof(u32)) ){
      u32 *aCopy = lsmMallocRc(pDb->pEnv, sizeof(u32) * nCkpt, &rc);
      if( aCopy ){
        memcpy(aCopy, aData, nCkpt*sizeof(u32));
        ckptChangeEndianness(aCopy, nCkpt);
        if( ckptChecksumOk(aCopy) ){
          *piId = lsmCheckpointId(aCopy, 0);
          if( piLog ) *piLog = lsmCheckpointLogOffset(aCopy);
        }
        lsmFree(pDb->pEnv, aCopy);
      }
    }
    lsmFsMetaPageRelease(pPg);
  }

................................................................................
  DbLog *pLog
){ 
  u32 iOffMSB = aCkpt[CKPT_HDR_LO_MSW];
  u32 iOffLSB = aCkpt[CKPT_HDR_LO_LSW];
  pLog->aRegion[2].iStart = (((i64)iOffMSB) << 32) + ((i64)iOffLSB);
  pLog->cksum0 = aCkpt[CKPT_HDR_LO_CKSUM1];
  pLog->cksum1 = aCkpt[CKPT_HDR_LO_CKSUM2];
  pLog->iSnapshotId = lsmCheckpointId(aCkpt, 0);
}

void lsmCheckpointZeroLogoffset(lsm_db *pDb){
  u32 nCkpt;

  nCkpt = pDb->aSnapshot[CKPT_HDR_NCKPT];
  assert( nCkpt>CKPT_HDR_NCKPT );

static i64 firstByteOnSector(LogWriter *pLog, i64 iOff){
  return (iOff / pLog->szSector) * pLog->szSector;
}
static i64 lastByteOnSector(LogWriter *pLog, i64 iOff){
  return firstByteOnSector(pLog, iOff) + pLog->szSector - 1;
}





























/*
** This function is called when a write-transaction is first opened. It
** is assumed that the caller is holding the client-mutex when it is 
** called.
**
** Before returning, this function allocates the LogWriter object that
................................................................................
  if( pDb->bUseLog==0 ) return LSM_OK;
  rc = lsmFsOpenLog(pDb->pFS);
  pNew = lsmMallocZeroRc(pDb->pEnv, sizeof(LogWriter), &rc);
  if( pNew ){
    lsmStringInit(&pNew->buf, pDb->pEnv);
    rc = lsmStringExtend(&pNew->buf, 2);
  }














  if( rc!=LSM_OK ){
    assert( pNew==0 || pNew->buf.z==0 );
    lsmFree(pDb->pEnv, pNew);
    return rc;
  }

  /* Set the effective sector-size for this transaction. Sectors are assumed
................................................................................
    }
  }
  lsmStringClear(&p->buf);
  lsmFree(pDb->pEnv, p);
  pDb->pLogWriter = 0;
}

/*
** This function is called after a checkpoint is synced into the database
** file. The checkpoint specifies that the log starts at offset iOff.
** The shared state in *pLog is updated to reflect the fact that space
** in the log file that occurs logically before offset iOff may now
** be reused.
*/ 
void lsmLogCheckpoint(lsm_db *pDb, lsm_i64 iOff){
  DbLog *pLog = &pDb->treehdr.log;
  int iRegion;

  for(iRegion=0; iRegion<3; iRegion++){
    LogRegion *p = &pLog->aRegion[iRegion];
    if( iOff>=p->iStart && iOff<=p->iEnd ) break;
    p->iStart = 0;
    p->iEnd = 0;
  }
  assert( iRegion<3 );

  pLog->aRegion[iRegion].iStart = iOff;
}

static int jumpIfRequired(
  lsm_db *pDb,
  LogWriter *pLog,
  int nReq,
  int *pbJump
){
  /* Determine if it is necessary to add an LSM_LOG_JUMP to jump over the

static i64 firstByteOnSector(LogWriter *pLog, i64 iOff){
  return (iOff / pLog->szSector) * pLog->szSector;
}
static i64 lastByteOnSector(LogWriter *pLog, i64 iOff){
  return firstByteOnSector(pLog, iOff) + pLog->szSector - 1;
}

/*
** If possible, reclaim log file space. Log file space is reclaimed after
** a snapshot that points to the same data in the database file is synced
** into the db header.
*/
static int logReclaimSpace(lsm_db *pDb){
  int rc = LSM_OK;
  if( pDb->pShmhdr->iMetaPage ){
    DbLog *pLog = &pDb->treehdr.log;
    i64 iSnapshotId = 0;
    i64 iOff = 0;
    rc = lsmCheckpointSynced(pDb, &iSnapshotId, &iOff);
    if( rc==LSM_OK && pLog->iSnapshotId<iSnapshotId ){
      int iRegion;
      for(iRegion=0; iRegion<3; iRegion++){
        LogRegion *p = &pLog->aRegion[iRegion];
        if( iOff>=p->iStart && iOff<=p->iEnd ) break;
        p->iStart = 0;
        p->iEnd = 0;
      }
      assert( iRegion<3 );
      pLog->aRegion[iRegion].iStart = iOff;
      pLog->iSnapshotId = iSnapshotId;
    }
  }
  return rc;
}

/*
** This function is called when a write-transaction is first opened. It
** is assumed that the caller is holding the client-mutex when it is 
** called.
**
** Before returning, this function allocates the LogWriter object that
................................................................................
  if( pDb->bUseLog==0 ) return LSM_OK;
  rc = lsmFsOpenLog(pDb->pFS);
  pNew = lsmMallocZeroRc(pDb->pEnv, sizeof(LogWriter), &rc);
  if( pNew ){
    lsmStringInit(&pNew->buf, pDb->pEnv);
    rc = lsmStringExtend(&pNew->buf, 2);
  }
  if( rc==LSM_OK ){
    /* The following call detects whether or not a new snapshot has been 
    ** synced into the database file. If so, it updates the contents of
    ** the pDb->treehdr.log structure to reclaim any space in the log
    ** file that is no longer required. 
    **
    ** TODO: Calling this every transaction is overkill. And since the 
    ** call has to read and checksum a snapshot from the database file,
    ** it is expensive. It would be better to figure out a way so that
    ** this is only called occasionally - say for every 32KB written to 
    ** the log file.
    */
    rc = logReclaimSpace(pDb);
  }
  if( rc!=LSM_OK ){
    assert( pNew==0 || pNew->buf.z==0 );
    lsmFree(pDb->pEnv, pNew);
    return rc;
  }

  /* Set the effective sector-size for this transaction. Sectors are assumed
................................................................................
    }
  }
  lsmStringClear(&p->buf);
  lsmFree(pDb->pEnv, p);
  pDb->pLogWriter = 0;
}























static int jumpIfRequired(
  lsm_db *pDb,
  LogWriter *pLog,
  int nReq,
  int *pbJump
){
  /* Determine if it is necessary to add an LSM_LOG_JUMP to jump over the

    /* The "is in use" bit */
    rc = lsmLsmInUse(pDb, iFree, &bInUse);

    /* The "has been checkpointed" bit */
    if( rc==LSM_OK && bInUse==0 ){
      i64 iId = 0;
      rc = lsmCheckpointSynced(pDb, &iId);
      if( rc!=LSM_OK || iId<iFree ) bInUse = 1;
    }

    if( rc==LSM_OK && bInUse==0 ){
      iRet = pFree->aEntry[0].iBlk;
      flRemoveEntry0(pFree);
      assert( iRet!=0 );
................................................................................
      rc = lsmFsSyncDb(pDb->pFS);
      if( rc==LSM_OK ) rc = lsmCheckpointStore(pDb, iMeta);
      if( rc==LSM_OK ) rc = lsmFsSyncDb(pDb->pFS);
      if( rc==LSM_OK ) pShm->iMetaPage = iMeta;
    }
  }

  /* If no error has occured, then the snapshot currently in pDb->aSnapshot
  ** has been synced to disk. This means it may be possible to wrap the
  ** log file. Obtain the WRITER lock and update the relevent tree-header
  ** fields to reflect this. 
  */
  if( rc==LSM_OK ){
    u64 iLogoff = lsmCheckpointLogOffset(pDb->aSnapshot);
    if( pDb->nTransOpen==0 ){
      rc = lsmShmLock(pDb, LSM_LOCK_WRITER, LSM_LOCK_EXCL, 0);
    }
    if( rc==LSM_OK ){
      rc = lsmTreeLoadHeader(pDb);
      if( rc==LSM_OK ) lsmLogCheckpoint(pDb, iLogoff);
      if( rc==LSM_OK ) lsmTreeEndTransaction(pDb, 1);
      if( rc==LSM_BUSY ) rc = LSM_OK;
      if( pDb->nTransOpen==0 ){
        rc = lsmShmLock(pDb, LSM_LOCK_WRITER, LSM_LOCK_UNLOCK, 0);
      }
    }
    if( rc==LSM_BUSY ) rc = LSM_OK;
  }

  lsmShmLock(pDb, LSM_LOCK_CHECKPOINTER, LSM_LOCK_UNLOCK, 0);
  return rc;
}

int lsmBeginWork(lsm_db *pDb){
  int rc;

    /* The "is in use" bit */
    rc = lsmLsmInUse(pDb, iFree, &bInUse);

    /* The "has been checkpointed" bit */
    if( rc==LSM_OK && bInUse==0 ){
      i64 iId = 0;
      rc = lsmCheckpointSynced(pDb, &iId, 0);
      if( rc!=LSM_OK || iId<iFree ) bInUse = 1;
    }

    if( rc==LSM_OK && bInUse==0 ){
      iRet = pFree->aEntry[0].iBlk;
      flRemoveEntry0(pFree);
      assert( iRet!=0 );
................................................................................
      rc = lsmFsSyncDb(pDb->pFS);
      if( rc==LSM_OK ) rc = lsmCheckpointStore(pDb, iMeta);
      if( rc==LSM_OK ) rc = lsmFsSyncDb(pDb->pFS);
      if( rc==LSM_OK ) pShm->iMetaPage = iMeta;
    }
  }























  lsmShmLock(pDb, LSM_LOCK_CHECKPOINTER, LSM_LOCK_UNLOCK, 0);
  return rc;
}

int lsmBeginWork(lsm_db *pDb){
  int rc;