SQLite

  int (*xBusyHandler)(void*); /* Function to call when busy */
  void *pBusyHandlerArg;      /* Context argument for xBusyHandler */
  int aStat[3];               /* Total cache hits, misses and writes */
#ifdef SQLITE_TEST
  int nRead;                  /* Database pages read */
#endif
  void (*xReiniter)(DbPage*); /* Call this routine when reloading pages */
  int (*xGet)(Pager*,Pgno,DbPage**,int); /* Routine to fetch a patch */
#ifdef SQLITE_HAS_CODEC
  void *(*xCodec)(void*,void*,Pgno,int); /* Routine for en/decoding data */
  void (*xCodecSizeChng)(void*,int,int); /* Notify of page size changes */
  void (*xCodecFree)(void*);             /* Destructor for the codec */
  void *pCodec;               /* First argument to xCodec... methods */
#endif
  char *pTmpSpace;            /* Pager.pageSize bytes of space for tmp use */

      , p->journalOff, p->journalHdr
      , (int)p->dbSize, (int)p->dbOrigSize, (int)p->dbFileSize
  );

  return zRet;
}
#endif

/* Forward references to the various page getters */
static int getPageNormal(Pager*,Pgno,DbPage**,int);
static int getPageMMap(Pager*,Pgno,DbPage**,int);
static int getPageError(Pager*,Pgno,DbPage**,int);

/*
** Set the Pager.xGet method for the appropriate routine used to fetch
** content from the pager.
*/
static void setGetterMethod(Pager *pPager){
  if( pPager->errCode ){
    pPager->xGet = getPageError;
  }else if( USEFETCH(pPager)
#ifdef SQLITE_HAS_CODEC
   && pPager->xCodec==0
#endif
  ){
    pPager->xGet = getPageMMap;
  }else{
    pPager->xGet = getPageNormal;
  }
}

/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
** or more open savepoints for which:
**
**   * The page-number is less than or equal to PagerSavepoint.nOrig, and

      pPager->changeCountDone = 0;
      pPager->eState = PAGER_OPEN;
    }else{
      pPager->eState = (isOpen(pPager->jfd) ? PAGER_OPEN : PAGER_READER);
    }
    if( USEFETCH(pPager) ) sqlite3OsUnfetch(pPager->fd, 0, 0);
    pPager->errCode = SQLITE_OK;
    setGetterMethod(pPager);
  }

  pPager->journalOff = 0;
  pPager->journalHdr = 0;
  pPager->setMaster = 0;
}

       pPager->errCode==SQLITE_FULL ||
       pPager->errCode==SQLITE_OK ||
       (pPager->errCode & 0xff)==SQLITE_IOERR
  );
  if( rc2==SQLITE_FULL || rc2==SQLITE_IOERR ){
    pPager->errCode = rc;
    pPager->eState = PAGER_ERROR;
    setGetterMethod(pPager);
  }
  return rc;
}

static int pager_truncate(Pager *pPager, Pgno nPage);

/*

static void pagerFixMaplimit(Pager *pPager){
#if SQLITE_MAX_MMAP_SIZE>0
  sqlite3_file *fd = pPager->fd;
  if( isOpen(fd) && fd->pMethods->iVersion>=3 ){
    sqlite3_int64 sz;
    sz = pPager->szMmap;
    pPager->bUseFetch = (sz>0);
    setGetterMethod(pPager);
    sqlite3OsFileControlHint(pPager->fd, SQLITE_FCNTL_MMAP_SIZE, &sz);
  }
#endif
}

/*
** Change the maximum size of any memory mapping made of the database file.

    pPager->journalMode = PAGER_JOURNALMODE_OFF;
  }else if( memDb ){
    pPager->journalMode = PAGER_JOURNALMODE_MEMORY;
  }
  /* pPager->xBusyHandler = 0; */
  /* pPager->pBusyHandlerArg = 0; */
  pPager->xReiniter = xReinit;
  setGetterMethod(pPager);
  /* memset(pPager->aHash, 0, sizeof(pPager->aHash)); */
  /* pPager->szMmap = SQLITE_DEFAULT_MMAP_SIZE // will be set by btree.c */

  *ppPager = pPager;
  return SQLITE_OK;
}

** to find a page in the in-memory cache first.  If the page is not already
** in memory, this routine goes to disk to read it in whereas Lookup()
** just returns 0.  This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since Lookup() never goes to disk, it never has to deal with locks
** or journal files.
*/
static int getPageNormal(
  Pager *pPager,      /* The pager open on the database file */
  Pgno pgno,          /* Page number to fetch */
  DbPage **ppPage,    /* Write a pointer to the page here */
  int flags           /* PAGER_GET_XXX flags */
){
  int rc = SQLITE_OK;
  PgHdr *pPg = 0;
  u32 iFrame = 0;                 /* Frame to read from WAL file */
  const int noContent = (flags & PAGER_GET_NOCONTENT);
  sqlite3_pcache_page *pBase;















  if( pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }
  assert( pPager->errCode==SQLITE_OK );
  assert( pPager->eState>=PAGER_READER );
  assert( assert_pager_state(pPager) );


  assert( pPager->hasHeldSharedLock==1 );








































  pBase = sqlite3PcacheFetch(pPager->pPCache, pgno, 3);
  if( pBase==0 ){
    rc = sqlite3PcacheFetchStress(pPager->pPCache, pgno, &pBase);
    if( rc!=SQLITE_OK ) goto pager_acquire_err;
    if( pBase==0 ){
      pPg = *ppPage = 0;
      rc = SQLITE_NOMEM_BKPT;
      goto pager_acquire_err;
    }
  }
  pPg = *ppPage = sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pBase);











  assert( pPg==(*ppPage) );
  assert( pPg->pgno==pgno );
  assert( pPg->pPager==pPager || pPg->pPager==0 );

  if( pPg->pPager && !noContent ){
    /* In this case the pcache already contains an initialized copy of
    ** the page. Return without further ado.  */

        TESTONLY( rc = ) addToSavepointBitvecs(pPager, pgno);
        testcase( rc==SQLITE_NOMEM );
        sqlite3EndBenignMalloc();
      }
      memset(pPg->pData, 0, pPager->pageSize);
      IOTRACE(("ZERO %p %d\n", pPager, pgno));
    }else{
      if( pagerUseWal(pPager) /*&& bMmapOk==0*/ ){
        rc = sqlite3WalFindFrame(pPager->pWal, pgno, &iFrame);
        if( rc!=SQLITE_OK ) goto pager_acquire_err;
      }
      assert( pPg->pPager==pPager );
      pPager->aStat[PAGER_STAT_MISS]++;
      rc = readDbPage(pPg, iFrame);
      if( rc!=SQLITE_OK ){
        goto pager_acquire_err;
      }
    }
    pager_set_pagehash(pPg);
  }

  return SQLITE_OK;

pager_acquire_err:
  assert( rc!=SQLITE_OK );
  if( pPg ){
    sqlite3PcacheDrop(pPg);
  }
  pagerUnlockIfUnused(pPager);
  *ppPage = 0;
  return rc;
}

/* The page getter for when memory-mapped I/O is enabled */
static int getPageMMap(
  Pager *pPager,      /* The pager open on the database file */
  Pgno pgno,          /* Page number to fetch */
  DbPage **ppPage,    /* Write a pointer to the page here */
  int flags           /* PAGER_GET_XXX flags */
){
  int rc = SQLITE_OK;
  PgHdr *pPg = 0;
  u32 iFrame = 0;                 /* Frame to read from WAL file */

  assert( USEFETCH(pPager) );
#ifdef SQLITE_HAS_CODEC
  assert( pPager->xCodec==0 );
#endif

  /* It is acceptable to use a read-only (mmap) page for any page except
  ** page 1 if there is no write-transaction open or the ACQUIRE_READONLY
  ** flag was specified by the caller. And so long as the db is not a 
  ** temporary or in-memory database.  */
  const int bMmapOk = (pgno>1
   && (pPager->eState==PAGER_READER || (flags & PAGER_GET_READONLY))
  );

  /* Optimization note:  Adding the "pgno<=1" term before "pgno==0" here
  ** allows the compiler optimizer to reuse the results of the "pgno>1"
  ** test in the previous statement, and avoid testing pgno==0 in the
  ** common case where pgno is large. */
  if( pgno<=1 && pgno==0 ){
    return SQLITE_CORRUPT_BKPT;
  }
  assert( pPager->eState>=PAGER_READER );
  assert( assert_pager_state(pPager) );
  assert( pPager->hasHeldSharedLock==1 );
  assert( pPager->errCode==SQLITE_OK );

  if( bMmapOk && pagerUseWal(pPager) ){
    rc = sqlite3WalFindFrame(pPager->pWal, pgno, &iFrame);
    if( rc!=SQLITE_OK ){
      *ppPage = 0;
      return rc;
    }
  }
  if( bMmapOk && iFrame==0 ){
    void *pData = 0;
    rc = sqlite3OsFetch(pPager->fd, 
        (i64)(pgno-1) * pPager->pageSize, pPager->pageSize, &pData
    );
    if( rc==SQLITE_OK && pData ){
      if( pPager->eState>PAGER_READER || pPager->tempFile ){
        pPg = sqlite3PagerLookup(pPager, pgno);
      }
      if( pPg==0 ){
        rc = pagerAcquireMapPage(pPager, pgno, pData, &pPg);
     }else{
        sqlite3OsUnfetch(pPager->fd, (i64)(pgno-1)*pPager->pageSize, pData);
      }
      if( pPg ){
        assert( rc==SQLITE_OK );
        *ppPage = pPg;
        return SQLITE_OK;
      }
    }
    if( rc!=SQLITE_OK ){
      *ppPage = 0;
      return rc;
    }
  }
  return getPageNormal(pPager, pgno, ppPage, flags);
}

/* The page getter method for when the pager is an error state */
static int getPageError(
  Pager *pPager,      /* The pager open on the database file */
  Pgno pgno,          /* Page number to fetch */
  DbPage **ppPage,    /* Write a pointer to the page here */
  int flags           /* PAGER_GET_XXX flags */
){
  assert( pPager->errCode!=SQLITE_OK );
  *ppPage = 0;
  return pPager->errCode;
}


/* Dispatch all page fetch requests to the appropriate getter method.
*/
int sqlite3PagerGet(
  Pager *pPager,      /* The pager open on the database file */
  Pgno pgno,          /* Page number to fetch */
  DbPage **ppPage,    /* Write a pointer to the page here */
  int flags           /* PAGER_GET_XXX flags */
){
  return pPager->xGet(pPager, pgno, ppPage, flags);
}

/*
** Acquire a page if it is already in the in-memory cache.  Do
** not read the page from disk.  Return a pointer to the page,
** or 0 if the page is not in cache. 
**

    if( !MEMDB && eState>PAGER_WRITER_LOCKED ){
      /* This can happen using journal_mode=off. Move the pager to the error 
      ** state to indicate that the contents of the cache may not be trusted.
      ** Any active readers will get SQLITE_ABORT.
      */
      pPager->errCode = SQLITE_ABORT;
      pPager->eState = PAGER_ERROR;
      setGetterMethod(pPager);
      return rc;
    }
  }else{
    rc = pager_playback(pPager, 0);
  }

  assert( pPager->eState==PAGER_READER || rc!=SQLITE_OK );

    ** can be rolled back at the ZipVFS level.  */
    else if( 
        pPager->journalMode==PAGER_JOURNALMODE_OFF 
     && pPager->eState>=PAGER_WRITER_CACHEMOD
    ){
      pPager->errCode = SQLITE_ABORT;
      pPager->eState = PAGER_ERROR;
      setGettterMethod(pPager);
    }
#endif
  }

  return rc;
}

  void *pCodec
){
  if( pPager->xCodecFree ) pPager->xCodecFree(pPager->pCodec);
  pPager->xCodec = pPager->memDb ? 0 : xCodec;
  pPager->xCodecSizeChng = xCodecSizeChng;
  pPager->xCodecFree = xCodecFree;
  pPager->pCodec = pCodec;
  setGetterMethod(pPager);
  pagerReportSize(pPager);
}
void *sqlite3PagerGetCodec(Pager *pPager){
  return pPager->pCodec;
}

/*