int sqlite4BtLogClose(BtLog*, int bCleanup);

int sqlite4BtLogRead(BtLog*, u32 pgno, u8 *aData);
int sqlite4BtLogWrite(BtLog*, u32 pgno, u8 *aData, int bCommit);

int sqlite4BtLogSnapshotOpen(BtLog*);
int sqlite4BtLogSnapshotClose(BtLog*);

int sqlite4BtLogSnapshotWritable(BtLog*);


int sqlite4BtLogSize(BtLog*);
int sqlite4BtLogCheckpoint(BtLog*);

int sqlite4BtLogFrameToIdx(u32 *aLog, u32 iFrame);

#ifndef NDEBUG
................................................................................
int sqlite4BtLockWriterUnlock(BtLock*);

/* Obtain and release CHECKPOINTER lock */
int sqlite4BtLockCkpt(BtLock*);
int sqlite4BtLockCkptUnlock(BtLock*);

/* Obtain and release READER locks.  */
int sqlite4BtLockReader(BtLock*, u32 *aLog, BtReadSlot *aLock);
int sqlite4BtLockReaderUnlock(BtLock*);

/* Query READER locks.  */
int sqlite4BtLockReaderQuery(BtLock*, u32*, BtReadSlot*, u32*, int*);

/* Obtain pointers to shared-memory chunks */
int sqlite4BtLockShmMap(BtLock*, int iChunk, int nByte, u8 **ppOut);

int sqlite4BtLogClose(BtLog*, int bCleanup);

int sqlite4BtLogRead(BtLog*, u32 pgno, u8 *aData);
int sqlite4BtLogWrite(BtLog*, u32 pgno, u8 *aData, int bCommit);

int sqlite4BtLogSnapshotOpen(BtLog*);
int sqlite4BtLogSnapshotClose(BtLog*);

int sqlite4BtLogSnapshotWrite(BtLog*);
int sqlite4BtLogSnapshotEndWrite(BtLog*);

int sqlite4BtLogSize(BtLog*);
int sqlite4BtLogCheckpoint(BtLog*);

int sqlite4BtLogFrameToIdx(u32 *aLog, u32 iFrame);

#ifndef NDEBUG
................................................................................
int sqlite4BtLockWriterUnlock(BtLock*);

/* Obtain and release CHECKPOINTER lock */
int sqlite4BtLockCkpt(BtLock*);
int sqlite4BtLockCkptUnlock(BtLock*);

/* Obtain and release READER locks.  */
int sqlite4BtLockReader(BtLock*, u32 *aLog, u32 iFirst, BtReadSlot *aLock);
int sqlite4BtLockReaderUnlock(BtLock*);

/* Query READER locks.  */
int sqlite4BtLockReaderQuery(BtLock*, u32*, BtReadSlot*, u32*, int*);

/* Obtain pointers to shared-memory chunks */
int sqlite4BtLockShmMap(BtLock*, int iChunk, int nByte, u8 **ppOut);

** Argument aLog points to an array of 6 frame addresses. These are the 
** first and last frames in each of log regions A, B and C. Argument 
** aLock points to the array of read-lock slots in shared memory.
*/
int sqlite4BtLockReader(
  BtLock *pLock,                  /* Lock module handle */
  u32 *aLog,                      /* Current log file topology */

  BtReadSlot *aSlot               /* Array of read-lock slots (in shmem) */
){
  int rc = SQLITE4_BUSY;          /* Return code */
  int i;                          /* Loop counter */


  /* Find the first and last log frames that this client will use. */
  u32 iLast = aLog[5];











  u32 iFirst = 0;
  for(i=0; iFirst==0 && i<3; i++){
    iFirst = aLog[i*2];
  }

  if( iFirst==0 ){
    rc = btLockLockop(pLock, BT_LOCK_READER_DBONLY, BT_LOCK_SHARED, 0);
  }else{
    int nAttempt = 100;           /* Remaining lock attempts */

    while( rc==SQLITE4_BUSY && (nAttempt--)>0 ){

      /* Try to find a slot populated with the values required. */

** Argument aLog points to an array of 6 frame addresses. These are the 
** first and last frames in each of log regions A, B and C. Argument 
** aLock points to the array of read-lock slots in shared memory.
*/
int sqlite4BtLockReader(
  BtLock *pLock,                  /* Lock module handle */
  u32 *aLog,                      /* Current log file topology */
  u32 iFirst,                     /* First log frame to lock */
  BtReadSlot *aSlot               /* Array of read-lock slots (in shmem) */
){
  int rc = SQLITE4_BUSY;          /* Return code */
  int i;                          /* Loop counter */
  u32 iLast = aLog[5];            /* Last frame to lock */


  /* If page iFirst does not appear to be part of the log at all, then
  ** the entire log has been checkpointed (and iFirst is the "next" 
  ** frame to use). Handle this case in the same way as an empty 
  ** log file.  
  **
  ** It is also possible that the iFirst value (read from the shared-memory
  ** checkpoint header) is much newer than the aLog[] values (read from
  ** the snapshot header). If so, the caller will figure it out.  */
  if( iFirst<aLog[0] && iFirst>aLog[1] 
   && iFirst<aLog[2] && iFirst>aLog[3] 
   && iFirst<aLog[4] && iFirst>aLog[5] 
  ){
    iLast = 0;


  }

  if( iLast==0 ){
    rc = btLockLockop(pLock, BT_LOCK_READER_DBONLY, BT_LOCK_SHARED, 0);
  }else{
    int nAttempt = 100;           /* Remaining lock attempts */

    while( rc==SQLITE4_BUSY && (nAttempt--)>0 ){

      /* Try to find a slot populated with the values required. */

    if( nAttempt==0 ) rc = SQLITE4_PROTOCOL;
  }

  return rc;
}

int sqlite4BtLogSnapshotOpen(BtLog *pLog){

  int rc = SQLITE4_NOTFOUND;
  BtShmHdr shmhdr;


  while( rc==SQLITE4_NOTFOUND ){


    /* Attempt to read a copy of the BtShmHdr from shared-memory. */
    rc = btLogSnapshot(pLog, &pLog->snapshot);

    /* Take a read lock on the database */
    if( rc==SQLITE4_OK ){
      BtReadSlot *aReadlock = btLogShm(pLog)->aReadlock;




      rc = sqlite4BtLockReader(pLog->pLock, pLog->snapshot.aLog, aReadlock);
    }

    /* Check that the BtShmHdr in shared-memory has not changed. If it has,
    ** drop the read-lock and re-attempt the entire operation. */
    if( rc==SQLITE4_OK ){
      rc = btLogSnapshot(pLog, &shmhdr);
    }


    if( rc==SQLITE4_OK && memcmp(&shmhdr, &pLog->snapshot, sizeof(BtShmHdr)) ){
      sqlite4BtLockReaderUnlock(pLog->pLock);

      rc = SQLITE4_NOTFOUND;





    }
  }




  if( rc==SQLITE4_OK ){
    int iRegion;
    u32 *aLog = pLog->snapshot.aLog;
    BtShm *pShm = btLogShm(pLog);
    u32 iCkpt = pShm->ckpt.iFirstRecover;

    for(iRegion=0; iRegion<3; iRegion++){
      if( aLog[iRegion*2] ){
        if( iCkpt>=aLog[iRegion*2] && iCkpt<=aLog[iRegion*2+1] ){

          aLog[iRegion*2] = iCkpt;
          break;
        }else{
          aLog[iRegion*2] = 0;
          aLog[iRegion*2+1] = 0;
        }
      }
    }

  }

  return rc;
}

int sqlite4BtLogSnapshotClose(BtLog *pLog){
  sqlite4BtLockReaderUnlock(pLog->pLock);
  return SQLITE4_OK;
}






int sqlite4BtLogSnapshotWritable(BtLog *pLog){































































  return 1;




}

static void btLogMergeInplace(
  u32 *aLeft, int nLeft,          /* Left hand input array */
  u32 *aRight, int nRight,        /* Right hand input array */
  u32 *aSpace,                    /* Temporary space */
  int *pnOut                      /* OUT: Size of aLeft[] after merge */
................................................................................
    ** writers that it is now safe to recycle pages before this point
    ** (assuming all live readers are cleared).  */
    if( rc==SQLITE4_OK ){
      pShm->ckpt.iFirstRecover = iFirstRead;
      pVfs->xShmBarrier(pLog->pFd);
    }

    /* Free the buffer and drop the checkpointer lock */
    sqlite4_free(pLock->pEnv, aBuf);

    sqlite4BtLockCkptUnlock(pLog->pLock);
  }
  return rc;
}

    if( nAttempt==0 ) rc = SQLITE4_PROTOCOL;
  }

  return rc;
}

int sqlite4BtLogSnapshotOpen(BtLog *pLog){
  u32 *aLog = pLog->snapshot.aLog;
  int rc = SQLITE4_NOTFOUND;
  BtShmHdr shmhdr;
  u32 iFirstRead = 0;

  while( rc==SQLITE4_NOTFOUND ){
    BtShm *pShm;

    /* Attempt to read a copy of the BtShmHdr from shared-memory. */
    rc = btLogSnapshot(pLog, &pLog->snapshot);

    /* Take a read lock on the database */
    if( rc==SQLITE4_OK ){
      BtReadSlot *aReadlock;
      pShm = btLogShm(pLog);

      aReadlock = pShm->aReadlock;
      iFirstRead = pShm->ckpt.iFirstRead;
      rc = sqlite4BtLockReader(pLog->pLock, aLog, iFirstRead, aReadlock);
    }

    /* Check that the BtShmHdr in shared-memory has not changed. If it has,
    ** drop the read-lock and re-attempt the entire operation. */
    if( rc==SQLITE4_OK ){
      rc = btLogSnapshot(pLog, &shmhdr);
    }
    if( rc==SQLITE4_OK ){
      if( iFirstRead!=pShm->ckpt.iFirstRead 
       || memcmp(&shmhdr, &pLog->snapshot, sizeof(BtShmHdr)) 

      ){
        rc = SQLITE4_NOTFOUND;
      }
    }
    
    if( rc!=SQLITE4_OK ){
      sqlite4BtLockReaderUnlock(pLog->pLock);
    }
  }

  /* If a snapshot was successfully read, adjust it so that the aLog[] 
  ** array specifies that no frames before iFirstRead is ever read from 
  ** the log file.  */
  if( rc==SQLITE4_OK ){
    int iRegion;




    for(iRegion=0; iRegion<3; iRegion++){
      if( aLog[iRegion*2] ){

        if( iFirstRead>=aLog[iRegion*2] && iFirstRead<=aLog[iRegion*2+1] ){
          aLog[iRegion*2] = iFirstRead;
          break;
        }else{
          aLog[iRegion*2] = 0;
          aLog[iRegion*2+1] = 0;
        }
      }
    }

  }

  return rc;
}

int sqlite4BtLogSnapshotClose(BtLog *pLog){
  sqlite4BtLockReaderUnlock(pLog->pLock);
  return SQLITE4_OK;
}

/*
** The log handle has already successfully opened a read-only snapshot
** when this function is called. This function attempts to upgrade it
** to a read-write snapshot. 
*/
int sqlite4BtLogSnapshotWrite(BtLog *pLog){
  BtLock *pLock = pLog->pLock;
  int rc;

  rc = sqlite4BtLockWriter(pLock);
  if( rc==SQLITE4_OK ){
    BtShm *pShm = btLogShm(pLog);
    BtShmHdr shmhdr;

    /* Check if this connection is currently reading from the latest
    ** database snapshot. Set rc to SQLITE4_BUSY if it is not.  */
    rc = btLogSnapshot(pLog, &shmhdr);
    if( rc==SQLITE4_OK && memcmp(&pShm->hdr1, &pShm->hdr2, sizeof(BtShmHdr)) ){
      memcpy(&pShm->hdr1, &shmhdr, sizeof(BtShmHdr));
      memcpy(&pShm->hdr2, &shmhdr, sizeof(BtShmHdr));
    }
    if( rc==SQLITE4_OK && pLog->snapshot.iNextFrame!=shmhdr.iNextFrame ){
      rc = SQLITE4_BUSY;
    }

    /* Currently, pLog->snapshot.aLog[] contains a map of the frames
    ** that this connection was required to consider in order to read
    ** from the read-only snapshot. The following block edits this so
    ** that it contains a map of all frames that are currently in use
    ** by any reader, or may be used by any future reader or recovery
    ** process.  */
    if( rc==SQLITE4_OK ){
      u32 *aLog = shmhdr.aLog;
      u32 iRecover = pShm->ckpt.iFirstRecover;
      u32 iRead = 0;

      rc = sqlite4BtLockReaderQuery(pLock, aLog, pShm->aReadlock, &iRead, 0);

      if( rc==SQLITE4_OK ){
        /* Now "trim" the snapshot so that it accesses nothing earlier than
        ** either iRecover or iRead (whichever occurs first in the log). */
        u32 iTrim = iRecover;
        if( iRead ){
          int iIdxRead = sqlite4BtLogFrameToIdx(aLog, iRead);
          if( sqlite4BtLogFrameToIdx(aLog, iRecover)>iIdxRead ) iTrim = iRead;
        }

        if( iTrim==0 || iTrim==shmhdr.iNextFrame || btLogIsEmpty(pLog) ){
          memset(aLog, 0, sizeof(u32)*6);
        }else{
          int i;
          for(i=0; i<3; i++){
            int bIn = (aLog[2*i]<=iTrim && iTrim<=aLog[2*i+1]);
            if( bIn ){
              aLog[2*i] = iTrim;
              break;
            }else{
              aLog[2*i] = aLog[2*i+1] = 0;
            }
          }
        }
      }

      if( rc==SQLITE4_OK ){
        memcpy(pLog->snapshot.aLog, aLog, sizeof(u32)*6);
      }
    }
  }

  return rc;
}

int sqlite4BtLogSnapshotEndWrite(BtLog *pLog){
  return sqlite4BtLockWriterUnlock(pLog->pLock);
}

static void btLogMergeInplace(
  u32 *aLeft, int nLeft,          /* Left hand input array */
  u32 *aRight, int nRight,        /* Right hand input array */
  u32 *aSpace,                    /* Temporary space */
  int *pnOut                      /* OUT: Size of aLeft[] after merge */
................................................................................
    ** writers that it is now safe to recycle pages before this point
    ** (assuming all live readers are cleared).  */
    if( rc==SQLITE4_OK ){
      pShm->ckpt.iFirstRecover = iFirstRead;
      pVfs->xShmBarrier(pLog->pFd);
    }

    /* Free buffers and drop the checkpointer lock */
    sqlite4_free(pLock->pEnv, aBuf);
    sqlite4_free(pLock->pEnv, aPgno);
    sqlite4BtLockCkptUnlock(pLog->pLock);
  }
  return rc;
}

/*;
** 2013 September 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
................................................................................
  if( rc==SQLITE4_OK ){
    /* If the read transaction was successfully opened, the transaction 
    ** level is now 1.  */
    p->iTransactionLevel = 1;
  }
  return rc;
}










static int btCloseReadTransaction(BtPager *p){
  int rc;
  assert( p->iTransactionLevel==0 );
  rc = sqlite4BtLogSnapshotClose(p->pLog);

  /* Purge the page cache. */
................................................................................
    pPg->pNextDirty = 0;
    if( rc==SQLITE4_OK ){
      int bCommit = (pNext==0);
      rc = sqlite4BtLogWrite(p->pLog, pPg->pgno, pPg->aData, bCommit);
    }
  }
  p->pDirty = 0;



  if( rc==SQLITE4_OK ){
    rc = p->btl.pVfs->xWrite(p->btl.pFd, 0, (void*)&p->dbhdr, sizeof(BtDbhdr));
  }

  if( p->nAutoCkpt && sqlite4BtLogSize(p->pLog)>=p->nAutoCkpt ){
    p->bDoAutoCkpt = 1;
  }
................................................................................
      btHashRemove(p, pPg);
      btFreePage(p, pPg);
    }else if( rc==SQLITE4_OK && (pPg->pgno<=p->dbhdr.nPg) ){
      rc = btLoadPageData(p, pPg);
    }
  }
  p->pDirty = 0;


  return rc;
}

/*
** Transactions. These methods are more or less the same as their 
** counterparts in bt.h.
................................................................................
  assert( p->btl.pFd );

  if( p->iTransactionLevel<iLevel ){
    /* Open a read transaction if one is not already open */
    if( p->iTransactionLevel==0 ){
      rc = btOpenReadTransaction(p);
    }






    if( rc==SQLITE4_OK ){
      assert( p->iTransactionLevel>=1 && iLevel>=p->iTransactionLevel );
      p->iTransactionLevel = iLevel;
    }
  }

/*
** 2013 September 14
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
................................................................................
  if( rc==SQLITE4_OK ){
    /* If the read transaction was successfully opened, the transaction 
    ** level is now 1.  */
    p->iTransactionLevel = 1;
  }
  return rc;
}

static int btOpenWriteTransaction(BtPager *p){
  int rc;
  assert( p->iTransactionLevel==1 );
  assert( p->btl.pFd );

  rc = sqlite4BtLogSnapshotWrite(p->pLog);
  return rc;
}

static int btCloseReadTransaction(BtPager *p){
  int rc;
  assert( p->iTransactionLevel==0 );
  rc = sqlite4BtLogSnapshotClose(p->pLog);

  /* Purge the page cache. */
................................................................................
    pPg->pNextDirty = 0;
    if( rc==SQLITE4_OK ){
      int bCommit = (pNext==0);
      rc = sqlite4BtLogWrite(p->pLog, pPg->pgno, pPg->aData, bCommit);
    }
  }
  p->pDirty = 0;
  sqlite4BtLogSnapshotEndWrite(p->pLog);

  /* TODO: Fix this. */
  if( rc==SQLITE4_OK ){
    rc = p->btl.pVfs->xWrite(p->btl.pFd, 0, (void*)&p->dbhdr, sizeof(BtDbhdr));
  }

  if( p->nAutoCkpt && sqlite4BtLogSize(p->pLog)>=p->nAutoCkpt ){
    p->bDoAutoCkpt = 1;
  }
................................................................................
      btHashRemove(p, pPg);
      btFreePage(p, pPg);
    }else if( rc==SQLITE4_OK && (pPg->pgno<=p->dbhdr.nPg) ){
      rc = btLoadPageData(p, pPg);
    }
  }
  p->pDirty = 0;
  sqlite4BtLogSnapshotEndWrite(p->pLog);

  return rc;
}

/*
** Transactions. These methods are more or less the same as their 
** counterparts in bt.h.
................................................................................
  assert( p->btl.pFd );

  if( p->iTransactionLevel<iLevel ){
    /* Open a read transaction if one is not already open */
    if( p->iTransactionLevel==0 ){
      rc = btOpenReadTransaction(p);
    }

    /* Open a write transaction if one is required */
    if( rc==SQLITE4_OK && p->iTransactionLevel<2 && iLevel>=2 ){
      rc = btOpenWriteTransaction(p);
    }

    if( rc==SQLITE4_OK ){
      assert( p->iTransactionLevel>=1 && iLevel>=p->iTransactionLevel );
      p->iTransactionLevel = iLevel;
    }
  }

do_execsql_test 1.8 {
  DELETE FROM t1 WHERE 1;
}

do_execsql_test 1.9 {
  SELECT * FROM t1;
  DROP TABLE t1;



  SELECT * FROM sqlite_kvstore;
}

#--------------------------------------------------------------------------

set val [string repeat x 200]
do_execsql_test 2.0 {

do_execsql_test 1.8 {
  DELETE FROM t1 WHERE 1;
}

do_execsql_test 1.9 {
  SELECT * FROM t1;
  DROP TABLE t1;
}

do_execsql_test 1.10 {
  SELECT * FROM sqlite_kvstore;
}

#--------------------------------------------------------------------------

set val [string repeat x 200]
do_execsql_test 2.0 {