int sqlite4BtPagerPagesize(BtPager*);

/* 
** Query for the db header values. Requires an open read transaction or
** an active checkpoint.
*/
BtDbHdr *sqlite4BtPagerDbhdr(BtPager*);


/*
** Used by checkpointers to specify the header to use during a checkpoint.
*/
void sqlite4BtPagerSetDbhdr(BtPager *, BtDbHdr *);

/*
................................................................................
int sqlite4BtLogPagesize(BtLog*);
int sqlite4BtLogPagecount(BtLog*);
u32 sqlite4BtLogCookie(BtLog*);
#endif
BtDbHdr *sqlite4BtLogDbhdr(BtLog*);

int sqlite4BtLogSetCookie(BtLog*, u32 iCookie);


/*
** End of bt_log.c interface.
*************************************************************************/

/*************************************************************************
** Interface to bt_lock.c functionality.

int sqlite4BtPagerPagesize(BtPager*);

/* 
** Query for the db header values. Requires an open read transaction or
** an active checkpoint.
*/
BtDbHdr *sqlite4BtPagerDbhdr(BtPager*);
void sqlite4BtPagerDbhdrDirty(BtPager*);

/*
** Used by checkpointers to specify the header to use during a checkpoint.
*/
void sqlite4BtPagerSetDbhdr(BtPager *, BtDbHdr *);

/*
................................................................................
int sqlite4BtLogPagesize(BtLog*);
int sqlite4BtLogPagecount(BtLog*);
u32 sqlite4BtLogCookie(BtLog*);
#endif
BtDbHdr *sqlite4BtLogDbhdr(BtLog*);

int sqlite4BtLogSetCookie(BtLog*, u32 iCookie);
int sqlite4BtLogDbhdrFlush(BtLog*);

/*
** End of bt_log.c interface.
*************************************************************************/

/*************************************************************************
** Interface to bt_lock.c functionality.

  u32 iLast;                      /* Frame containing last commit flag in log */
  u32 iNextFrame;                 /* Frame that follows frame iLast */
  u32 iPageOneFrame;              /* Frame containing most recent page 1 */
};

static int btLogRecoverFrame(
  BtLog *pLog,                    /* Log module handle */
  void *pCtx,                     /* woints to type u32 - pgno of last commit*/
  u32 iFrame,                     /* Frame number */
  BtFrameHdr *pHdr                /* Frame header */
){
  FrameRecoverCtx *pFRC = (FrameRecoverCtx*)pCtx;

  if( btLogIsEmpty(pLog) ){
    /* This is the first frame recovered. It is therefore both the first
................................................................................
}
#endif

BtDbHdr *sqlite4BtLogDbhdr(BtLog *pLog){
  return &pLog->snapshot.dbhdr;
}


















/*
** Set the value of the user cookie.
*/
int sqlite4BtLogSetCookie(BtLog *pLog, u32 iCookie){
  BtPager *pPager = (BtPager *)(pLog->pLock);
  BtPage *pOne = 0;

  u32 iLast;                      /* Frame containing last commit flag in log */
  u32 iNextFrame;                 /* Frame that follows frame iLast */
  u32 iPageOneFrame;              /* Frame containing most recent page 1 */
};

static int btLogRecoverFrame(
  BtLog *pLog,                    /* Log module handle */
  void *pCtx,                     /* Pointer to FrameRecoverCtx */
  u32 iFrame,                     /* Frame number */
  BtFrameHdr *pHdr                /* Frame header */
){
  FrameRecoverCtx *pFRC = (FrameRecoverCtx*)pCtx;

  if( btLogIsEmpty(pLog) ){
    /* This is the first frame recovered. It is therefore both the first
................................................................................
}
#endif

BtDbHdr *sqlite4BtLogDbhdr(BtLog *pLog){
  return &pLog->snapshot.dbhdr;
}

int sqlite4BtLogDbhdrFlush(BtLog *pLog){
  BtPager *pPager = (BtPager *)(pLog->pLock);
  BtPage *pOne = 0;
  int rc;

  rc = sqlite4BtPageGet(pPager, 1, &pOne);
  if( rc==SQLITE4_OK ){
    rc = sqlite4BtPageWrite(pOne);
  }
  if( rc==SQLITE4_OK ){
    btLogUpdateDbhdr(pLog, sqlite4BtPageData(pOne));
  }
  sqlite4BtPageRelease(pOne);

  return rc;
} 

/*
** Set the value of the user cookie.
*/
int sqlite4BtLogSetCookie(BtLog *pLog, u32 iCookie){
  BtPager *pPager = (BtPager *)(pLog->pLock);
  BtPage *pOne = 0;

    btDumpCsr(&buf, &pSub->mcsr);

    sqlite4BtBufAppendf(&buf, "\n%d csr   : ", iBt);
    btDumpCsr(&buf, &pSub->csr);
    sqlite4BtBufAppendf(&buf, "\n");
  }


  fprintf(stderr, "%s", (char*)buf.p);
  sqlite4_buffer_clear(&buf);
}
#endif

#ifndef NDEBUG
/*
................................................................................
        BtCursor *pM = &pSub->mcsr;
        btCsrSetup(db, pHdr->iMRoot, pM);

        btPutU32(&pSub->aPrefix[0], (u32)iter.iAge);
        btPutU32(&pSub->aPrefix[4], ~(u32)iter.iLvl);

        rc = btCsrSeek(pM, pSub->aPrefix, pK, nK, BT_SEEK_LE, BT_CSRSEEK_SEEK);

        if( rc==SQLITE4_NOTFOUND && eSeek==BT_SEEK_GE ){
          rc = btCsrSeek(pM, pSub->aPrefix, 0, 0, BT_SEEK_GE, BT_CSRSEEK_SEEK);
        }

        if( rc==SQLITE4_INEXACT ){
          rc = fiSubCsrCheckPrefix(pSub);
        }

        if( rc==SQLITE4_NOTFOUND ){
          /* No keys to visit in this level */
          assert( pSub->mcsr.nPg==0 );
          assert( pSub->csr.nPg==0 );
          rc = SQLITE4_OK;
................................................................................
      btPutU32(&aPrefix[4], ~(u32)(iter.iLvl - (iter.iLvl==0 ? 0 : 1)));
      rc = btCsrSeek(&pSub->mcsr, 0, aPrefix, n, BT_SEEK_LE, 0);
      if( rc==SQLITE4_OK ){
        rc = btCsrStep(&pSub->mcsr, 0);
      }
    }
    if( rc==SQLITE4_INEXACT ) rc = SQLITE4_OK;


    if( rc==SQLITE4_OK ){
      const void *pV;
      int nV;
      int iRoot;
      btCsrData(&pSub->mcsr, 0, 4, &pV, &nV);
      iRoot = sqlite4BtGetU32((const u8*)pV);
      btCsrReset(&pSub->csr, 1);
      btCsrSetup(db, iRoot, &pSub->csr);
      rc = btCsrEnd(&pSub->csr, bLast);



    }
  }
  fiLevelIterCleanup(&iter);

  if( rc==SQLITE4_OK ){
    pCsr->base.flags &= ~(CSR_NEXT_OK | CSR_PREV_OK);
    pCsr->base.flags |= (bLast ? CSR_PREV_OK : CSR_NEXT_OK);
................................................................................
*/
int sqlite4BtCsrFirst(bt_cursor *pBase){
  int rc;
  if( IsBtCsr(pBase) ){
    rc = btCsrEnd((BtCursor*)pBase, 0);
  }else{
    rc = fiCsrEnd((FiCursor*)pBase, 0);

  }
  return rc;
}

/*
** Position cursor pCsr to point to the largest key in the database.
*/
int sqlite4BtCsrLast(bt_cursor *pBase){
  int rc;
  if( IsBtCsr(pBase) ){
    rc = btCsrEnd((BtCursor*)pBase, 1);
  }else{
    rc = fiCsrEnd((FiCursor*)pBase, 1);

  }
  return rc;
}


/*
** Advance to the next entry in the tree.
................................................................................
*/
static int btAllocateNonOverflow(bt_db *db, BtPage **ppPg){
  int rc;
  if( db->bFastInsertOp ){
    BtDbHdr *pHdr = sqlite4BtPagerDbhdr(db->pPager);
    u32 iPg;


    iPg = pHdr->nSubPg + btFirstOfBlock(pHdr, pHdr->iSubBlock);
    pHdr->nSubPg++;
    rc = sqlite4BtPageGet(db->pPager, iPg, ppPg);
    if( rc==SQLITE4_OK ){
      rc = sqlite4BtPageWrite(*ppPg);
      if( rc!=SQLITE4_OK ){
        sqlite4BtPageRelease(*ppPg);
................................................................................
    if( bLeaf && db->bFastInsertOp ){
      /* This operation will need to allocate further pages. The worst
      ** case scenario is (nDepth+1) pages. If fewer than that remain
      ** available in the block, return BT_BLOCKFULL. */
      BtDbHdr *pHdr = sqlite4BtPagerDbhdr(db->pPager);
      int nPgPerBlk = (pHdr->blksz / pHdr->pgsz);
      if( (nPgPerBlk - pHdr->nSubPg) < pCsr->nPg+1 ){

        rc = BT_BLOCKFULL;
        pHdr->iSubBlock = 0;
      }
    }
    if( rc==SQLITE4_OK && pCsr->nPg==1 ){
      rc = btExtendTree(pCsr);
    }
................................................................................

  /* Save the value of the fast-insert flag. It will be restored before
  ** this function returns. Leaving it set here interferes with page 
  ** allocation if the meta-tree needs to be extended.  */
  const int bFastInsertOp = db->bFastInsertOp;
  db->bFastInsertOp = 0;
  
#if 0

  fprintf(stderr, "BEFORE!\n");
  btPrintMetaTree(db->pPager, 1, pHdr);
#endif
  assert_summary_ok(db, SQLITE4_OK);

  memset(&csr, 0, sizeof(csr));
  memset(&mcsr, 0, sizeof(mcsr));
  btCsrSetup(db, pHdr->iMRoot, &mcsr);
................................................................................

      if( rc==SQLITE4_OK ){
        /* rc = btCsrStep(&mcsr, 1); */
        rc = btCsrSeek(&mcsr, 0, aPrefix, sizeof(aPrefix), BT_SEEK_GE, 0);
        if( rc==SQLITE4_INEXACT ) rc = SQLITE4_OK;
      }
    }


    if( rc==SQLITE4_NOTFOUND ){
      rc = SQLITE4_OK;
    }else if( rc==SQLITE4_OK && iRoot ){
      int n = sizeof(aPrefix) + nKey;
      rc = sqlite4_buffer_resize(&buf, n);
      if( rc==SQLITE4_OK ){
        u8 aData[4];
        u8 *a = (u8*)buf.p;
        memcpy(a, aPrefix, sizeof(aPrefix));
        memcpy(&a[sizeof(aPrefix)], pKey, nKey);
................................................................................
    }
  }

  btCsrReset(&csr, 1);
  btCsrReset(&mcsr, 1);
  sqlite4_buffer_clear(&buf);

#if 0
  if( rc==SQLITE4_OK ){
    btPrintMetaTree(db->pPager, 1, pHdr);
  }
#endif
  assert_summary_ok(db, SQLITE4_OK);
  db->bFastInsertOp = bFastInsertOp;
  return rc;
................................................................................

  /* Find the schedule page. If there is no schedule page, allocate it now. */
  if( pHdr->iSRoot==0 ){
    rc = sqlite4BtPageAllocate(db->pPager, &pPg);
    if( rc==SQLITE4_OK ){
      u8 *aData = sqlite4BtPageData(pPg);
      memset(aData, 0, pHdr->pgsz);

      pHdr->iSRoot = sqlite4BtPagePgno(pPg);
    }
  }else{
    rc = sqlite4BtPageGet(db->pPager, pHdr->iSRoot, &pPg);
  }

  /* Check if the schedule page is busy. If so, no new merge may be 
................................................................................
  int rc = SQLITE4_OK;

  assert( db->bFastInsertOp );
  db->bFastInsertOp = 0;

  /* If the meta-tree has not been created, create it now. */
  if( pHdr->iMRoot==0 ){

    rc = btAllocateNewRoot(db, BT_PGFLAGS_METATREE, &pHdr->iMRoot);
  }

  /* If no writable sub-tree current exists, create one */ 
  if( rc==SQLITE4_OK && pHdr->iSubBlock==0 ){
    u32 iLevel;                   /* Level number for new sub-tree */
    u32 iSubBlock;                /* New block */
................................................................................
    if( rc==SQLITE4_OK ){
      rc = btAllocateBlock(db, 1, &iSubBlock);
    }

    if( rc==SQLITE4_OK ){
      u8 aKey[8];
      u8 aVal[4];

      pHdr->iSubBlock = iSubBlock;
      pHdr->nSubPg = 1;           /* Root page is automatically allocated */

      /* The key for the new entry consists of the concatentation of two 
      ** 32-bit big-endian integers - the <age> and <level-no>. The age
      ** of the new segment is 0. The level number is one greater than the
      ** level number of the previous segment.  */
................................................................................
          nKey -= nPrefix;
          pKey = (const void*)(((const u8*)pKey) + nPrefix);
        }
      }
    }

    /* Assuming the process above found a block, set up the block cursor and
    ** seek it to the smallest first valid key.  */
    if( rc==SQLITE4_OK ){
      const void *pVal = 0; int nVal = 0;
      rc = btCsrData(pM, 0, 4, &pVal, &nVal);
      if( rc==SQLITE4_OK ){
        u32 iRoot = sqlite4BtGetU32((const u8*)pVal);
        btCsrSetup(db, iRoot, &pSub->csr);
        rc = btCsrSeek(&pSub->csr, 0, pKey, nKey, BT_SEEK_GE, 0);
        if( rc==SQLITE4_INEXACT ) rc = SQLITE4_OK;
        if( rc==SQLITE4_NOTFOUND ) rc = btErrorBkpt(SQLITE4_CORRUPT);



      }
    }else if( rc==SQLITE4_NOTFOUND ){
      assert( pSub->csr.nPg==0 );
      assert( pSub->mcsr.nPg==0 );
      rc = SQLITE4_OK;
    }
  }

    btDumpCsr(&buf, &pSub->mcsr);

    sqlite4BtBufAppendf(&buf, "\n%d csr   : ", iBt);
    btDumpCsr(&buf, &pSub->csr);
    sqlite4BtBufAppendf(&buf, "\n");
  }

  sqlite4_buffer_append(&buf, "", 1);
  fprintf(stderr, "%s", (char*)buf.p);
  sqlite4_buffer_clear(&buf);
}
#endif

#ifndef NDEBUG
/*
................................................................................
        BtCursor *pM = &pSub->mcsr;
        btCsrSetup(db, pHdr->iMRoot, pM);

        btPutU32(&pSub->aPrefix[0], (u32)iter.iAge);
        btPutU32(&pSub->aPrefix[4], ~(u32)iter.iLvl);

        rc = btCsrSeek(pM, pSub->aPrefix, pK, nK, BT_SEEK_LE, BT_CSRSEEK_SEEK);
        if( rc==SQLITE4_INEXACT ) rc = fiSubCsrCheckPrefix(pSub);
        if( rc==SQLITE4_NOTFOUND && eSeek==BT_SEEK_GE ){
          rc = btCsrSeek(pM, pSub->aPrefix, 0, 0, BT_SEEK_GE, BT_CSRSEEK_SEEK);



          if( rc==SQLITE4_INEXACT ) rc = fiSubCsrCheckPrefix(pSub);
        }

        if( rc==SQLITE4_NOTFOUND ){
          /* No keys to visit in this level */
          assert( pSub->mcsr.nPg==0 );
          assert( pSub->csr.nPg==0 );
          rc = SQLITE4_OK;
................................................................................
      btPutU32(&aPrefix[4], ~(u32)(iter.iLvl - (iter.iLvl==0 ? 0 : 1)));
      rc = btCsrSeek(&pSub->mcsr, 0, aPrefix, n, BT_SEEK_LE, 0);
      if( rc==SQLITE4_OK ){
        rc = btCsrStep(&pSub->mcsr, 0);
      }
    }
    if( rc==SQLITE4_INEXACT ) rc = SQLITE4_OK;
    if( rc==SQLITE4_OK ) rc = fiSubCsrCheckPrefix(pSub);

    if( rc==SQLITE4_OK ){
      const void *pV;
      int nV;
      int iRoot;
      btCsrData(&pSub->mcsr, 0, 4, &pV, &nV);
      iRoot = sqlite4BtGetU32((const u8*)pV);
      btCsrReset(&pSub->csr, 1);
      btCsrSetup(db, iRoot, &pSub->csr);
      rc = btCsrEnd(&pSub->csr, bLast);
    }else if( rc==SQLITE4_NOTFOUND ){
      btCsrReset(&pSub->mcsr, 0);
      rc = SQLITE4_OK;
    }
  }
  fiLevelIterCleanup(&iter);

  if( rc==SQLITE4_OK ){
    pCsr->base.flags &= ~(CSR_NEXT_OK | CSR_PREV_OK);
    pCsr->base.flags |= (bLast ? CSR_PREV_OK : CSR_NEXT_OK);
................................................................................
*/
int sqlite4BtCsrFirst(bt_cursor *pBase){
  int rc;
  if( IsBtCsr(pBase) ){
    rc = btCsrEnd((BtCursor*)pBase, 0);
  }else{
    rc = fiCsrEnd((FiCursor*)pBase, 0);
    assert_ficursor_ok((FiCursor*)pBase, rc);
  }
  return rc;
}

/*
** Position cursor pCsr to point to the largest key in the database.
*/
int sqlite4BtCsrLast(bt_cursor *pBase){
  int rc;
  if( IsBtCsr(pBase) ){
    rc = btCsrEnd((BtCursor*)pBase, 1);
  }else{
    rc = fiCsrEnd((FiCursor*)pBase, 1);
    assert_ficursor_ok((FiCursor*)pBase, rc);
  }
  return rc;
}


/*
** Advance to the next entry in the tree.
................................................................................
*/
static int btAllocateNonOverflow(bt_db *db, BtPage **ppPg){
  int rc;
  if( db->bFastInsertOp ){
    BtDbHdr *pHdr = sqlite4BtPagerDbhdr(db->pPager);
    u32 iPg;

    sqlite4BtPagerDbhdrDirty(db->pPager);
    iPg = pHdr->nSubPg + btFirstOfBlock(pHdr, pHdr->iSubBlock);
    pHdr->nSubPg++;
    rc = sqlite4BtPageGet(db->pPager, iPg, ppPg);
    if( rc==SQLITE4_OK ){
      rc = sqlite4BtPageWrite(*ppPg);
      if( rc!=SQLITE4_OK ){
        sqlite4BtPageRelease(*ppPg);
................................................................................
    if( bLeaf && db->bFastInsertOp ){
      /* This operation will need to allocate further pages. The worst
      ** case scenario is (nDepth+1) pages. If fewer than that remain
      ** available in the block, return BT_BLOCKFULL. */
      BtDbHdr *pHdr = sqlite4BtPagerDbhdr(db->pPager);
      int nPgPerBlk = (pHdr->blksz / pHdr->pgsz);
      if( (nPgPerBlk - pHdr->nSubPg) < pCsr->nPg+1 ){
        sqlite4BtPagerDbhdrDirty(db->pPager);
        rc = BT_BLOCKFULL;
        pHdr->iSubBlock = 0;
      }
    }
    if( rc==SQLITE4_OK && pCsr->nPg==1 ){
      rc = btExtendTree(pCsr);
    }
................................................................................

  /* Save the value of the fast-insert flag. It will be restored before
  ** this function returns. Leaving it set here interferes with page 
  ** allocation if the meta-tree needs to be extended.  */
  const int bFastInsertOp = db->bFastInsertOp;
  db->bFastInsertOp = 0;
  
#if 1
  static int nCall = 0; nCall++;
  fprintf(stderr, "BEFORE %d\n", nCall);
  btPrintMetaTree(db->pPager, 1, pHdr);
#endif
  assert_summary_ok(db, SQLITE4_OK);

  memset(&csr, 0, sizeof(csr));
  memset(&mcsr, 0, sizeof(mcsr));
  btCsrSetup(db, pHdr->iMRoot, &mcsr);
................................................................................

      if( rc==SQLITE4_OK ){
        /* rc = btCsrStep(&mcsr, 1); */
        rc = btCsrSeek(&mcsr, 0, aPrefix, sizeof(aPrefix), BT_SEEK_GE, 0);
        if( rc==SQLITE4_INEXACT ) rc = SQLITE4_OK;
      }
    }
    if( rc==SQLITE4_NOTFOUND ) rc = SQLITE4_OK;



    if( rc==SQLITE4_OK && iRoot ){
      int n = sizeof(aPrefix) + nKey;
      rc = sqlite4_buffer_resize(&buf, n);
      if( rc==SQLITE4_OK ){
        u8 aData[4];
        u8 *a = (u8*)buf.p;
        memcpy(a, aPrefix, sizeof(aPrefix));
        memcpy(&a[sizeof(aPrefix)], pKey, nKey);
................................................................................
    }
  }

  btCsrReset(&csr, 1);
  btCsrReset(&mcsr, 1);
  sqlite4_buffer_clear(&buf);

#if 1
  if( rc==SQLITE4_OK ){
    btPrintMetaTree(db->pPager, 1, pHdr);
  }
#endif
  assert_summary_ok(db, SQLITE4_OK);
  db->bFastInsertOp = bFastInsertOp;
  return rc;
................................................................................

  /* Find the schedule page. If there is no schedule page, allocate it now. */
  if( pHdr->iSRoot==0 ){
    rc = sqlite4BtPageAllocate(db->pPager, &pPg);
    if( rc==SQLITE4_OK ){
      u8 *aData = sqlite4BtPageData(pPg);
      memset(aData, 0, pHdr->pgsz);
      sqlite4BtPagerDbhdrDirty(db->pPager);
      pHdr->iSRoot = sqlite4BtPagePgno(pPg);
    }
  }else{
    rc = sqlite4BtPageGet(db->pPager, pHdr->iSRoot, &pPg);
  }

  /* Check if the schedule page is busy. If so, no new merge may be 
................................................................................
  int rc = SQLITE4_OK;

  assert( db->bFastInsertOp );
  db->bFastInsertOp = 0;

  /* If the meta-tree has not been created, create it now. */
  if( pHdr->iMRoot==0 ){
    sqlite4BtPagerDbhdrDirty(db->pPager);
    rc = btAllocateNewRoot(db, BT_PGFLAGS_METATREE, &pHdr->iMRoot);
  }

  /* If no writable sub-tree current exists, create one */ 
  if( rc==SQLITE4_OK && pHdr->iSubBlock==0 ){
    u32 iLevel;                   /* Level number for new sub-tree */
    u32 iSubBlock;                /* New block */
................................................................................
    if( rc==SQLITE4_OK ){
      rc = btAllocateBlock(db, 1, &iSubBlock);
    }

    if( rc==SQLITE4_OK ){
      u8 aKey[8];
      u8 aVal[4];
      sqlite4BtPagerDbhdrDirty(db->pPager);
      pHdr->iSubBlock = iSubBlock;
      pHdr->nSubPg = 1;           /* Root page is automatically allocated */

      /* The key for the new entry consists of the concatentation of two 
      ** 32-bit big-endian integers - the <age> and <level-no>. The age
      ** of the new segment is 0. The level number is one greater than the
      ** level number of the previous segment.  */
................................................................................
          nKey -= nPrefix;
          pKey = (const void*)(((const u8*)pKey) + nPrefix);
        }
      }
    }

    /* Assuming the process above found a block, set up the block cursor and
    ** seek it to the smallest valid key.  */
    if( rc==SQLITE4_OK ){
      const void *pVal = 0; int nVal = 0;
      rc = btCsrData(pM, 0, 4, &pVal, &nVal);
      if( rc==SQLITE4_OK ){
        u32 iRoot = sqlite4BtGetU32((const u8*)pVal);
        btCsrSetup(db, iRoot, &pSub->csr);
        rc = btCsrSeek(&pSub->csr, 0, pKey, nKey, BT_SEEK_GE, 0);
        if( rc==SQLITE4_INEXACT ) rc = SQLITE4_OK;
        if( rc==SQLITE4_NOTFOUND ){
          btCsrReset(pM, 0);
          rc = SQLITE4_OK;
        }
      }
    }else if( rc==SQLITE4_NOTFOUND ){
      assert( pSub->csr.nPg==0 );
      assert( pSub->mcsr.nPg==0 );
      rc = SQLITE4_OK;
    }
  }

/*
** Candidate values for BtPage.flags
*/
#define BT_PAGE_DIRTY 0x0001      /* Set for pages in BtPager.pDirty list */

/*
** Pager object.


*/
struct BtPager {
  BtLock btl;                     /* Variables shared with bt_lock module */
  BtLog *pLog;                    /* Logging module */
  int iTransactionLevel;          /* Current transaction level (see bt.h) */
  char *zFile;                    /* Database file name */
  int nFile;                      /* Length of string zFile in bytes */
................................................................................
  BtPageHash hash;                /* Hash table */
  BtPage *pDirty;                 /* List of all dirty pages */
  int nTotalRef;                  /* Total number of outstanding page refs */
  int bDoAutoCkpt;                /* Do auto-checkpoint after next unlock */
  BtSavepoint *aSavepoint;        /* Savepoint array */
  int nSavepoint;                 /* Number of entries in aSavepoint array */
  BtDbHdr *pHdr;                  /* Header object for current read snapshot */

  void *pLogsizeCtx;              /* A copy of this is passed to xLogsize() */
  void (*xLogsize)(void*, int);   /* Log-size Callback function */
};


/**************************************************************************
** Interface to BtPageHash object.
................................................................................
  if( rc==SQLITE4_OK && p->bDoAutoCkpt ){
    sqlite4BtLogCheckpoint(p->pLog, (p->btl.nAutoCkpt / 2));
  }
  p->bDoAutoCkpt = 0;

  return rc;
}










/*
** Commit the current write transaction to disk.
*/
static int btCommitTransaction(BtPager *p){
  int rc = SQLITE4_OK;
  int nLogsize;                   /* Number of frames in log after commit */
  BtPage *pPg;
  BtPage *pNext;
  assert( p->iTransactionLevel>=2 );


  btCloseSavepoints(p, 2, 0);

  for(pPg=p->pDirty; pPg; pPg=pNext){
    pNext = pPg->pNextDirty;
    pPg->flags &= ~(BT_PAGE_DIRTY);
    pPg->pNextDirty = 0;
    if( rc==SQLITE4_OK ){
      int nPg = ((pNext==0) ? p->pHdr->nPg : 0);
      rc = sqlite4BtLogWrite(p->pLog, pPg->pgno, pPg->aData, nPg);
    }
................................................................................

/* 
** Query for the root page number. Requires an open read transaction.
*/
BtDbHdr *sqlite4BtPagerDbhdr(BtPager *p){
  return p->pHdr;
}





void sqlite4BtPagerSetDbhdr(BtPager *p, BtDbHdr *pHdr){
  assert( p->pHdr==0 || pHdr==0 );
  p->pHdr = pHdr;
}

/*
................................................................................
    if( pPg==0 ){
      rc = sqlite4BtPageGet(p, pgno, &pRelease);
    }
    if( rc==SQLITE4_OK ){
      BtPage *pTrunk = pPg ? pPg : pRelease;
      rc = sqlite4BtPageWrite(pTrunk);
      if( rc==SQLITE4_OK ){

        sqlite4BtPutU32(&pTrunk->aData[0], 0);
        sqlite4BtPutU32(&pTrunk->aData[4], pHdr->iFreePg);
        pHdr->iFreePg = pgno;
        sqlite4BtDebugPageFree((BtLock*)p, "free-list-trunk", pgno);
      }
    }
    sqlite4BtPageRelease(pRelease);
................................................................................
      rc = sqlite4BtPageWrite(pTrunk);
    }
    if( rc==SQLITE4_OK ){
      u8 *aData = pTrunk->aData;
      u32 nFree = sqlite4BtGetU32(aData);
      if( nFree==0 ){
        u32 iNext = sqlite4BtGetU32(&aData[4]);

        *pPgno = pHdr->iFreePg;
        pHdr->iFreePg = iNext;
        sqlite4BtDebugPageAlloc((BtLock*)p, "free-list-trunk", *pPgno);
      }else{
        *pPgno = sqlite4BtGetU32(&aData[8 + 4*(nFree-1)]);
        sqlite4BtPutU32(aData, nFree-1);
        sqlite4BtDebugPageAlloc((BtLock*)p, "free-list", *pPgno);

/*
** Candidate values for BtPage.flags
*/
#define BT_PAGE_DIRTY 0x0001      /* Set for pages in BtPager.pDirty list */

/*
** Pager object.
**
** bDirtyHdr:
*/
struct BtPager {
  BtLock btl;                     /* Variables shared with bt_lock module */
  BtLog *pLog;                    /* Logging module */
  int iTransactionLevel;          /* Current transaction level (see bt.h) */
  char *zFile;                    /* Database file name */
  int nFile;                      /* Length of string zFile in bytes */
................................................................................
  BtPageHash hash;                /* Hash table */
  BtPage *pDirty;                 /* List of all dirty pages */
  int nTotalRef;                  /* Total number of outstanding page refs */
  int bDoAutoCkpt;                /* Do auto-checkpoint after next unlock */
  BtSavepoint *aSavepoint;        /* Savepoint array */
  int nSavepoint;                 /* Number of entries in aSavepoint array */
  BtDbHdr *pHdr;                  /* Header object for current read snapshot */
  int bDirtyHdr;                  /* True if pHdr has been modified */
  void *pLogsizeCtx;              /* A copy of this is passed to xLogsize() */
  void (*xLogsize)(void*, int);   /* Log-size Callback function */
};


/**************************************************************************
** Interface to BtPageHash object.
................................................................................
  if( rc==SQLITE4_OK && p->bDoAutoCkpt ){
    sqlite4BtLogCheckpoint(p->pLog, (p->btl.nAutoCkpt / 2));
  }
  p->bDoAutoCkpt = 0;

  return rc;
}

int btPagerDbhdrFlush(BtPager *p){
  int rc = SQLITE4_OK;
  if( p->bDirtyHdr ){
    rc = sqlite4BtLogDbhdrFlush(p->pLog);
    p->bDirtyHdr = 0;
  }
  return rc;
}

/*
** Commit the current write transaction to disk.
*/
static int btCommitTransaction(BtPager *p){
  int rc = SQLITE4_OK;
  int nLogsize;                   /* Number of frames in log after commit */
  BtPage *pPg;
  BtPage *pNext;
  assert( p->iTransactionLevel>=2 );

  rc = btPagerDbhdrFlush(p);
  btCloseSavepoints(p, 2, 0);

  for(pPg=p->pDirty; rc==SQLITE4_OK && pPg; pPg=pNext){
    pNext = pPg->pNextDirty;
    pPg->flags &= ~(BT_PAGE_DIRTY);
    pPg->pNextDirty = 0;
    if( rc==SQLITE4_OK ){
      int nPg = ((pNext==0) ? p->pHdr->nPg : 0);
      rc = sqlite4BtLogWrite(p->pLog, pPg->pgno, pPg->aData, nPg);
    }
................................................................................

/* 
** Query for the root page number. Requires an open read transaction.
*/
BtDbHdr *sqlite4BtPagerDbhdr(BtPager *p){
  return p->pHdr;
}

void sqlite4BtPagerDbhdrDirty(BtPager *p){
  p->bDirtyHdr = 1;
}

void sqlite4BtPagerSetDbhdr(BtPager *p, BtDbHdr *pHdr){
  assert( p->pHdr==0 || pHdr==0 );
  p->pHdr = pHdr;
}

/*
................................................................................
    if( pPg==0 ){
      rc = sqlite4BtPageGet(p, pgno, &pRelease);
    }
    if( rc==SQLITE4_OK ){
      BtPage *pTrunk = pPg ? pPg : pRelease;
      rc = sqlite4BtPageWrite(pTrunk);
      if( rc==SQLITE4_OK ){
        sqlite4BtPagerDbhdrDirty(p);
        sqlite4BtPutU32(&pTrunk->aData[0], 0);
        sqlite4BtPutU32(&pTrunk->aData[4], pHdr->iFreePg);
        pHdr->iFreePg = pgno;
        sqlite4BtDebugPageFree((BtLock*)p, "free-list-trunk", pgno);
      }
    }
    sqlite4BtPageRelease(pRelease);
................................................................................
      rc = sqlite4BtPageWrite(pTrunk);
    }
    if( rc==SQLITE4_OK ){
      u8 *aData = pTrunk->aData;
      u32 nFree = sqlite4BtGetU32(aData);
      if( nFree==0 ){
        u32 iNext = sqlite4BtGetU32(&aData[4]);
        sqlite4BtPagerDbhdrDirty(p);
        *pPgno = pHdr->iFreePg;
        pHdr->iFreePg = iNext;
        sqlite4BtDebugPageAlloc((BtLock*)p, "free-list-trunk", *pPgno);
      }else{
        *pPgno = sqlite4BtGetU32(&aData[8 + 4*(nFree-1)]);
        sqlite4BtPutU32(aData, nFree-1);
        sqlite4BtDebugPageAlloc((BtLock*)p, "free-list", *pPgno);

<p> As well as the records that index all segments in the db, the meta-table
contains a single summary record. The key is four 0xFF bytes.

<p>For each age between 0 and the largest age in the db, inclusive:

  * current minimum level number (16-bits).
  * total number of levels.
  * maximum level in active merge (16-bits).

Store this as a separate record in the meta-table. Even if there segments with
age=31 in the db, this is still only 6*32=192 bytes.

<h3> Schedule-Page Format</h3>

<p> As well as the records that index all segments in the db, the meta-table
contains a single summary record. The key is four 0xFF bytes.

<p>For each age between 0 and the largest age in the db, inclusive:

  * current minimum level number (16-bits).
  * total number of levels. (16-bits)
  * maximum level in active merge (16-bits).

Store this as a separate record in the meta-table. Even if there segments with
age=31 in the db, this is still only 6*32=192 bytes.

<h3> Schedule-Page Format</h3>