** the tree depth.  Root pages return 0.  Parents of root pages
** return 1, and so forth.
** 
** These checks are done:
**
**      1.  Make sure that cells and freeblocks do not overlap
**          but combine to completely cover the page.
**  NO  2.  Make sure cell keys are in order.
**  NO  3.  Make sure no key is less than or equal to zLowerBound.
**  NO  4.  Make sure no key is greater than or equal to zUpperBound.
**      5.  Check the integrity of overflow pages.
**      6.  Recursively call checkTreePage on all children.
**      7.  Verify that the depth of all children is the same.
**      8.  Make sure this page is at least 33% full or else it is
**          the root of the tree.
*/
static int checkTreePage(
  IntegrityCk *pCheck,  /* Context for the sanity check */
  int iPage,            /* Page number of the page to check */
  i64 *pnParentMinKey, 
  i64 *pnParentMaxKey
){
  MemPage *pPage;
  int i, rc, depth, d2, pgno, cnt;
  int hdr, cellStart;
  int nCell;
  u8 *data;
  BtShared *pBt;
  int usableSize;
  u32 *heap = 0;
................................................................................
  /* Clear MemPage.isInit to make sure the corruption detection code in
  ** btreeInitPage() is executed.  */
  pPage->isInit = 0;
  if( (rc = btreeInitPage(pPage))!=0 ){
    assert( rc==SQLITE_CORRUPT );  /* The only possible error from InitPage */
    checkAppendMsg(pCheck,
                   "btreeInitPage() returns error code %d", rc);
    releasePage(pPage);
    depth = -1;
    goto end_of_check;
  }

  /* Check out all the cells.
  */
  depth = 0;

  for(i=0; i<pPage->nCell && pCheck->mxErr; i++){
    u8 *pCell;
    u32 sz;
    CellInfo info;

    /* Check payload overflow pages
    */
    pCheck->zPfx = "On tree page %d cell %d: ";
    pCheck->v1 = iPage;
    pCheck->v2 = i;
    pCell = findCell(pPage,i);
    pPage->xParseCell(pPage, pCell, &info);
    sz = info.nPayload;
    /* For intKey pages, check that the keys are in order.
    */
    if( pPage->intKey ){
................................................................................
      depth = d2;
    }
  }

  if( !pPage->leaf ){
    pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    pCheck->zPfx = "On page %d at right child: ";
    pCheck->v1 = iPage;
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum ){
      checkPtrmap(pCheck, pgno, PTRMAP_BTREE, iPage);
    }
#endif
    checkTreePage(pCheck, pgno, NULL, !pPage->nCell?NULL:&nMaxKey);



  }
 
  /* For intKey leaf pages, check that the min/max keys are in order
  ** with any left/parent/right pages.
  */
  pCheck->zPfx = "Page %d: ";
  pCheck->v1 = iPage;
  if( pPage->leaf && pPage->intKey ){
    /* if we are a left child page */
    if( pnParentMinKey ){
      /* if we are the left most child page */
      if( !pnParentMaxKey ){
        if( nMaxKey > *pnParentMinKey ){
          checkAppendMsg(pCheck,
................................................................................
    }
  }

  /* Check for complete coverage of the page
  */
  data = pPage->aData;
  hdr = pPage->hdrOffset;
  heap = (u32*)sqlite3PageMalloc( pBt->pageSize );

  pCheck->zPfx = 0;
  if( heap==0 ){
    pCheck->mallocFailed = 1;
  }else{

    int contentOffset = get2byteNotZero(&data[hdr+5]);
    assert( contentOffset<=usableSize );  /* Enforced by btreeInitPage() */
    heap[0] = 0;
    btreeHeapInsert(heap, contentOffset-1);
    /* EVIDENCE-OF: R-37002-32774 The two-byte integer at offset 3 gives the
    ** number of cells on the page. */
    nCell = get2byte(&data[hdr+3]);
    /* EVIDENCE-OF: R-23882-45353 The cell pointer array of a b-tree page
    ** immediately follows the b-tree page header. */
    cellStart = hdr + 12 - 4*pPage->leaf;
................................................................................
    */
    if( heap[0]==0 && cnt!=data[hdr+7] ){
      checkAppendMsg(pCheck,
          "Fragmentation of %d bytes reported as %d on page %d",
          cnt, data[hdr+7], iPage);
    }
  }
  sqlite3PageFree(heap);
  releasePage(pPage);

end_of_check:

  pCheck->zPfx = saved_zPfx;
  pCheck->v1 = saved_v1;
  pCheck->v2 = saved_v2;
  return depth+1;
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

................................................................................
  Btree *p,     /* The btree to be checked */
  int *aRoot,   /* An array of root pages numbers for individual trees */
  int nRoot,    /* Number of entries in aRoot[] */
  int mxErr,    /* Stop reporting errors after this many */
  int *pnErr    /* Write number of errors seen to this variable */
){
  Pgno i;
  int nRef;
  IntegrityCk sCheck;
  BtShared *pBt = p->pBt;
  char zErr[100];

  sqlite3BtreeEnter(p);
  assert( p->inTrans>TRANS_NONE && pBt->inTransaction>TRANS_NONE );
  nRef = sqlite3PagerRefcount(pBt->pPager);
  sCheck.pBt = pBt;
  sCheck.pPager = pBt->pPager;
  sCheck.nPage = btreePagecount(sCheck.pBt);
  sCheck.mxErr = mxErr;
  sCheck.nErr = 0;
  sCheck.mallocFailed = 0;
  sCheck.zPfx = 0;
  sCheck.v1 = 0;
  sCheck.v2 = 0;
  *pnErr = 0;
  if( sCheck.nPage==0 ){
    sqlite3BtreeLeave(p);
    return 0;

  }

  sCheck.aPgRef = sqlite3MallocZero((sCheck.nPage / 8)+ 1);
  if( !sCheck.aPgRef ){
    *pnErr = 1;
    sqlite3BtreeLeave(p);
    return 0;
  }






  i = PENDING_BYTE_PAGE(pBt);
  if( i<=sCheck.nPage ) setPageReferenced(&sCheck, i);
  sqlite3StrAccumInit(&sCheck.errMsg, 0, zErr, sizeof(zErr), SQLITE_MAX_LENGTH);

  /* Check the integrity of the freelist
  */
  sCheck.zPfx = "Main freelist: ";
  checkList(&sCheck, 1, get4byte(&pBt->pPage1->aData[32]),
            get4byte(&pBt->pPage1->aData[36]));
  sCheck.zPfx = 0;
................................................................................
  for(i=0; (int)i<nRoot && sCheck.mxErr; i++){
    if( aRoot[i]==0 ) continue;
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum && aRoot[i]>1 ){
      checkPtrmap(&sCheck, aRoot[i], PTRMAP_ROOTPAGE, 0);
    }
#endif
    sCheck.zPfx = "List of tree roots: ";
    checkTreePage(&sCheck, aRoot[i], NULL, NULL);
    sCheck.zPfx = 0;
  }

  /* Make sure every page in the file is referenced
  */
  for(i=1; i<=sCheck.nPage && sCheck.mxErr; i++){
#ifdef SQLITE_OMIT_AUTOVACUUM
    if( getPageReferenced(&sCheck, i)==0 ){
................................................................................
    if( getPageReferenced(&sCheck, i)!=0 && 
       (PTRMAP_PAGENO(pBt, i)==i && pBt->autoVacuum) ){
      checkAppendMsg(&sCheck, "Pointer map page %d is referenced", i);
    }
#endif
  }

  /* Make sure this analysis did not leave any unref() pages.
  ** This is an internal consistency check; an integrity check
  ** of the integrity check.
  */
  if( NEVER(nRef != sqlite3PagerRefcount(pBt->pPager)) ){
    checkAppendMsg(&sCheck,
      "Outstanding page count goes from %d to %d during this analysis",
      nRef, sqlite3PagerRefcount(pBt->pPager)
    );
  }

  /* Clean  up and report errors.
  */
  sqlite3BtreeLeave(p);


  sqlite3_free(sCheck.aPgRef);
  if( sCheck.mallocFailed ){
    sqlite3StrAccumReset(&sCheck.errMsg);
    *pnErr = sCheck.nErr+1;
    return 0;
  }
  *pnErr = sCheck.nErr;
  if( sCheck.nErr==0 ) sqlite3StrAccumReset(&sCheck.errMsg);



  return sqlite3StrAccumFinish(&sCheck.errMsg);
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

/*
** Return the full pathname of the underlying database file.  Return
** an empty string if the database is in-memory or a TEMP database.

** the tree depth.  Root pages return 0.  Parents of root pages
** return 1, and so forth.
** 
** These checks are done:
**
**      1.  Make sure that cells and freeblocks do not overlap
**          but combine to completely cover the page.
**      2.  Make sure integer cell keys are in order.


**      3.  Check the integrity of overflow pages.
**      4.  Recursively call checkTreePage on all children.
**      5.  Verify that the depth of all children is the same.


*/
static int checkTreePage(
  IntegrityCk *pCheck,  /* Context for the sanity check */
  int iPage,            /* Page number of the page to check */
  i64 *pnParentMinKey, 
  i64 *pnParentMaxKey
){
  MemPage *pPage = 0;
  int i, rc, depth, d2, pgno, cnt;
  int hdr, cellStart;
  int nCell;
  u8 *data;
  BtShared *pBt;
  int usableSize;
  u32 *heap = 0;
................................................................................
  /* Clear MemPage.isInit to make sure the corruption detection code in
  ** btreeInitPage() is executed.  */
  pPage->isInit = 0;
  if( (rc = btreeInitPage(pPage))!=0 ){
    assert( rc==SQLITE_CORRUPT );  /* The only possible error from InitPage */
    checkAppendMsg(pCheck,
                   "btreeInitPage() returns error code %d", rc);

    depth = -1;
    goto end_of_check;
  }

  /* Check out all the cells.
  */
  depth = 0;
  pCheck->zPfx = "On tree page %d cell %d: ";
  for(i=0; i<pPage->nCell && pCheck->mxErr; i++){
    u8 *pCell;
    u32 sz;
    CellInfo info;

    /* Check payload overflow pages
    */


    pCheck->v2 = i;
    pCell = findCell(pPage,i);
    pPage->xParseCell(pPage, pCell, &info);
    sz = info.nPayload;
    /* For intKey pages, check that the keys are in order.
    */
    if( pPage->intKey ){
................................................................................
      depth = d2;
    }
  }

  if( !pPage->leaf ){
    pgno = get4byte(&pPage->aData[pPage->hdrOffset+8]);
    pCheck->zPfx = "On page %d at right child: ";

#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum ){
      checkPtrmap(pCheck, pgno, PTRMAP_BTREE, iPage);
    }
#endif
    d2 = checkTreePage(pCheck, pgno, NULL, !pPage->nCell?NULL:&nMaxKey);
    if( d2!=depth && iPage!=1 ){
      checkAppendMsg(pCheck, "Child page depth differs");
    }
  }
 
  /* For intKey leaf pages, check that the min/max keys are in order
  ** with any left/parent/right pages.
  */
  pCheck->zPfx = "Page %d: ";

  if( pPage->leaf && pPage->intKey ){
    /* if we are a left child page */
    if( pnParentMinKey ){
      /* if we are the left most child page */
      if( !pnParentMaxKey ){
        if( nMaxKey > *pnParentMinKey ){
          checkAppendMsg(pCheck,
................................................................................
    }
  }

  /* Check for complete coverage of the page
  */
  data = pPage->aData;
  hdr = pPage->hdrOffset;
  heap = pCheck->heap;
  heap[0] = 0;
  pCheck->zPfx = 0;



  {
    int contentOffset = get2byteNotZero(&data[hdr+5]);
    assert( contentOffset<=usableSize );  /* Enforced by btreeInitPage() */

    btreeHeapInsert(heap, contentOffset-1);
    /* EVIDENCE-OF: R-37002-32774 The two-byte integer at offset 3 gives the
    ** number of cells on the page. */
    nCell = get2byte(&data[hdr+3]);
    /* EVIDENCE-OF: R-23882-45353 The cell pointer array of a b-tree page
    ** immediately follows the b-tree page header. */
    cellStart = hdr + 12 - 4*pPage->leaf;
................................................................................
    */
    if( heap[0]==0 && cnt!=data[hdr+7] ){
      checkAppendMsg(pCheck,
          "Fragmentation of %d bytes reported as %d on page %d",
          cnt, data[hdr+7], iPage);
    }
  }



end_of_check:
  releasePage(pPage);
  pCheck->zPfx = saved_zPfx;
  pCheck->v1 = saved_v1;
  pCheck->v2 = saved_v2;
  return depth+1;
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

................................................................................
  Btree *p,     /* The btree to be checked */
  int *aRoot,   /* An array of root pages numbers for individual trees */
  int nRoot,    /* Number of entries in aRoot[] */
  int mxErr,    /* Stop reporting errors after this many */
  int *pnErr    /* Write number of errors seen to this variable */
){
  Pgno i;
  VVA_ONLY( int nRef );
  IntegrityCk sCheck;
  BtShared *pBt = p->pBt;
  char zErr[100];

  sqlite3BtreeEnter(p);
  assert( p->inTrans>TRANS_NONE && pBt->inTransaction>TRANS_NONE );
  assert( (nRef = sqlite3PagerRefcount(pBt->pPager))>=0 );
  sCheck.pBt = pBt;
  sCheck.pPager = pBt->pPager;
  sCheck.nPage = btreePagecount(sCheck.pBt);
  sCheck.mxErr = mxErr;
  sCheck.nErr = 0;
  sCheck.mallocFailed = 0;
  sCheck.zPfx = 0;
  sCheck.v1 = 0;
  sCheck.v2 = 0;
  sCheck.aPgRef = 0;
  sCheck.heap = 0;
  sqlite3StrAccumInit(&sCheck.errMsg, 0, zErr, sizeof(zErr), SQLITE_MAX_LENGTH);
  if( sCheck.nPage==0 ){
    goto integrity_ck_cleanup;
  }

  sCheck.aPgRef = sqlite3MallocZero((sCheck.nPage / 8)+ 1);
  if( !sCheck.aPgRef ){
    sCheck.mallocFailed = 1;
    goto integrity_ck_cleanup;

  }
  sCheck.heap = (u32*)sqlite3PageMalloc( pBt->pageSize );
  if( sCheck.heap==0 ){
    sCheck.mallocFailed = 1;
    goto integrity_ck_cleanup;
  }

  i = PENDING_BYTE_PAGE(pBt);
  if( i<=sCheck.nPage ) setPageReferenced(&sCheck, i);


  /* Check the integrity of the freelist
  */
  sCheck.zPfx = "Main freelist: ";
  checkList(&sCheck, 1, get4byte(&pBt->pPage1->aData[32]),
            get4byte(&pBt->pPage1->aData[36]));
  sCheck.zPfx = 0;
................................................................................
  for(i=0; (int)i<nRoot && sCheck.mxErr; i++){
    if( aRoot[i]==0 ) continue;
#ifndef SQLITE_OMIT_AUTOVACUUM
    if( pBt->autoVacuum && aRoot[i]>1 ){
      checkPtrmap(&sCheck, aRoot[i], PTRMAP_ROOTPAGE, 0);
    }
#endif

    checkTreePage(&sCheck, aRoot[i], NULL, NULL);

  }

  /* Make sure every page in the file is referenced
  */
  for(i=1; i<=sCheck.nPage && sCheck.mxErr; i++){
#ifdef SQLITE_OMIT_AUTOVACUUM
    if( getPageReferenced(&sCheck, i)==0 ){
................................................................................
    if( getPageReferenced(&sCheck, i)!=0 && 
       (PTRMAP_PAGENO(pBt, i)==i && pBt->autoVacuum) ){
      checkAppendMsg(&sCheck, "Pointer map page %d is referenced", i);
    }
#endif
  }












  /* Clean  up and report errors.
  */

integrity_ck_cleanup:
  sqlite3PageFree(sCheck.heap);
  sqlite3_free(sCheck.aPgRef);
  if( sCheck.mallocFailed ){
    sqlite3StrAccumReset(&sCheck.errMsg);
    sCheck.nErr++;

  }
  *pnErr = sCheck.nErr;
  if( sCheck.nErr==0 ) sqlite3StrAccumReset(&sCheck.errMsg);
  /* Make sure this analysis did not leave any unref() pages. */
  assert( nRef==sqlite3PagerRefcount(pBt->pPager) );
  sqlite3BtreeLeave(p);
  return sqlite3StrAccumFinish(&sCheck.errMsg);
}
#endif /* SQLITE_OMIT_INTEGRITY_CHECK */

/*
** Return the full pathname of the underlying database file.  Return
** an empty string if the database is in-memory or a TEMP database.

  Pgno nPage;       /* Number of pages in the database */
  int mxErr;        /* Stop accumulating errors when this reaches zero */
  int nErr;         /* Number of messages written to zErrMsg so far */
  int mallocFailed; /* A memory allocation error has occurred */
  const char *zPfx; /* Error message prefix */
  int v1, v2;       /* Values for up to two %d fields in zPfx */
  StrAccum errMsg;  /* Accumulate the error message text here */

};

/*
** Routines to read or write a two- and four-byte big-endian integer values.
*/
#define get2byte(x)   ((x)[0]<<8 | (x)[1])
#define put2byte(p,v) ((p)[0] = (u8)((v)>>8), (p)[1] = (u8)(v))

  Pgno nPage;       /* Number of pages in the database */
  int mxErr;        /* Stop accumulating errors when this reaches zero */
  int nErr;         /* Number of messages written to zErrMsg so far */
  int mallocFailed; /* A memory allocation error has occurred */
  const char *zPfx; /* Error message prefix */
  int v1, v2;       /* Values for up to two %d fields in zPfx */
  StrAccum errMsg;  /* Accumulate the error message text here */
  u32 *heap;        /* Min-heap used for analyzing cell coverage */
};

/*
** Routines to read or write a two- and four-byte big-endian integer values.
*/
#define get2byte(x)   ((x)[0]<<8 | (x)[1])
#define put2byte(p,v) ((p)[0] = (u8)((v)>>8), (p)[1] = (u8)(v))

** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
u8 sqlite3PagerIsreadonly(Pager *pPager){
  return pPager->readOnly;
}


/*
** Return the number of references to the pager.
*/
int sqlite3PagerRefcount(Pager *pPager){
  return sqlite3PcacheRefCount(pPager->pPCache);
}


/*
** Return the approximate number of bytes of memory currently
** used by the pager and its associated cache.
*/
int sqlite3PagerMemUsed(Pager *pPager){
  int perPageSize = pPager->pageSize + pPager->nExtra + sizeof(PgHdr)

** Return TRUE if the database file is opened read-only.  Return FALSE
** if the database is (in theory) writable.
*/
u8 sqlite3PagerIsreadonly(Pager *pPager){
  return pPager->readOnly;
}

#ifdef SQLITE_DEBUG
/*
** Return the number of references to the pager.
*/
int sqlite3PagerRefcount(Pager *pPager){
  return sqlite3PcacheRefCount(pPager->pPCache);
}
#endif

/*
** Return the approximate number of bytes of memory currently
** used by the pager and its associated cache.
*/
int sqlite3PagerMemUsed(Pager *pPager){
  int perPageSize = pPager->pageSize + pPager->nExtra + sizeof(PgHdr)

#ifdef SQLITE_ENABLE_ZIPVFS
  int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */
u8 sqlite3PagerIsreadonly(Pager*);
u32 sqlite3PagerDataVersion(Pager*);

int sqlite3PagerRefcount(Pager*);

int sqlite3PagerMemUsed(Pager*);
const char *sqlite3PagerFilename(Pager*, int);
const sqlite3_vfs *sqlite3PagerVfs(Pager*);
sqlite3_file *sqlite3PagerFile(Pager*);
const char *sqlite3PagerJournalname(Pager*);
int sqlite3PagerNosync(Pager*);
void *sqlite3PagerTempSpace(Pager*);

#ifdef SQLITE_ENABLE_ZIPVFS
  int sqlite3PagerWalFramesize(Pager *pPager);
#endif

/* Functions used to query pager state and configuration. */
u8 sqlite3PagerIsreadonly(Pager*);
u32 sqlite3PagerDataVersion(Pager*);
#ifdef SQLITE_DEBUG
  int sqlite3PagerRefcount(Pager*);
#endif
int sqlite3PagerMemUsed(Pager*);
const char *sqlite3PagerFilename(Pager*, int);
const sqlite3_vfs *sqlite3PagerVfs(Pager*);
sqlite3_file *sqlite3PagerFile(Pager*);
const char *sqlite3PagerJournalname(Pager*);
int sqlite3PagerNosync(Pager*);
void *sqlite3PagerTempSpace(Pager*);