SQLite

** is an instance of this class.
*/
struct MemJournal {
  const sqlite3_io_methods *pMethod; /* Parent class. MUST BE FIRST */
  int nChunkSize;                 /* In-memory chunk-size */

  int nSpill;                     /* Bytes of data before flushing */

  FileChunk *pFirst;              /* Head of in-memory chunk-list */
  FilePoint endpoint;             /* Pointer to the end of the file */
  FilePoint readpoint;            /* Pointer to the end of the last xRead() */

  int flags;                      /* xOpen flags */
  sqlite3_vfs *pVfs;              /* The "real" underlying VFS */
  const char *zJournal;           /* Name of the journal file */

  return SQLITE_OK;
}

/*
** Free the list of FileChunk structures headed at MemJournal.pFirst.
*/
static void memjrnlFreeChunks(FileChunk *pFirst){
  FileChunk *pIter;
  FileChunk *pNext;
  for(pIter=pFirst; pIter; pIter=pNext){
    pNext = pIter->pNext;
    sqlite3_free(pIter);
  } 

}

/*
** Flush the contents of memory to a real file on disk.
*/
static int memjrnlCreateFile(MemJournal *p){
  int rc;

      }
      rc = sqlite3OsWrite(pReal, (u8*)pIter->zChunk, nChunk, iOff);
      if( rc ) break;
      iOff += nChunk;
    }
    if( rc==SQLITE_OK ){
      /* No error has occurred. Free the in-memory buffers. */
      memjrnlFreeChunks(copy.pFirst);
    }
  }
  if( rc!=SQLITE_OK ){
    /* If an error occurred while creating or writing to the file, restore
    ** the original before returning. This way, SQLite uses the in-memory
    ** journal data to roll back changes made to the internal page-cache
    ** before this function was called.  */

        }

        memcpy((u8*)p->endpoint.pChunk->zChunk + iChunkOffset, zWrite, iSpace);
        zWrite += iSpace;
        nWrite -= iSpace;
        p->endpoint.iOffset += iSpace;
      }

    }
  }

  return SQLITE_OK;
}

/*
** Truncate the in-memory file.




*/
static int memjrnlTruncate(sqlite3_file *pJfd, sqlite_int64 size){
  MemJournal *p = (MemJournal *)pJfd;
  FileChunk *pIter = 0;

  if( size==0 ){
    memjrnlFreeChunks(p->pFirst);
    p->pFirst = 0;
  }else{
    i64 iOff = p->nChunkSize;
    for(pIter=p->pFirst; ALWAYS(pIter) && iOff<=size; pIter=pIter->pNext){
      iOff += p->nChunkSize;
    }
    if( pIter ){
      memjrnlFreeChunks(pIter->pNext);
      pIter->pNext = 0;
    }
  }

  p->endpoint.pChunk = pIter;
  p->endpoint.iOffset = size;
  p->readpoint.pChunk = 0;
  p->readpoint.iOffset = 0;

  return SQLITE_OK;
}

/*
** Close the file.
*/
static int memjrnlClose(sqlite3_file *pJfd){
  MemJournal *p = (MemJournal *)pJfd;
  memjrnlFreeChunks(p->pFirst);
  return SQLITE_OK;
}

/*
** Sync the file.
**
** If the real file has been created, call its xSync method. Otherwise, 

typedef struct PagerSavepoint PagerSavepoint;
struct PagerSavepoint {
  i64 iOffset;                 /* Starting offset in main journal */
  i64 iHdrOffset;              /* See above */
  Bitvec *pInSavepoint;        /* Set of pages in this savepoint */
  Pgno nOrig;                  /* Original number of pages in file */
  Pgno iSubRec;                /* Index of first record in sub-journal */
  int bTruncateOnRelease;      /* If stmt journal may be truncated on RELEASE */
#ifndef SQLITE_OMIT_WAL
  u32 aWalData[WAL_SAVEPOINT_NDATA];        /* WAL savepoint context */
#endif
};

/*
** Bits of the Pager.doNotSpill flag.  See further description below.

  Pager *pPager = pPg->pPager;
  PagerSavepoint *p;
  Pgno pgno = pPg->pgno;
  int i;
  for(i=0; i<pPager->nSavepoint; i++){
    p = &pPager->aSavepoint[i];
    if( p->nOrig>=pgno && 0==sqlite3BitvecTestNotNull(p->pInSavepoint, pgno) ){
      for(i=i+1; i<pPager->nSavepoint; i++){
        pPager->aSavepoint[i].bTruncateOnRelease = 0;
      }
      return 1;
    }
  }
  return 0;
}

#ifdef SQLITE_DEBUG

    if( isOpen(pPager->jfd) && pPager->journalOff>0 ){
      aNew[ii].iOffset = pPager->journalOff;
    }else{
      aNew[ii].iOffset = JOURNAL_HDR_SZ(pPager);
    }
    aNew[ii].iSubRec = pPager->nSubRec;
    aNew[ii].pInSavepoint = sqlite3BitvecCreate(pPager->dbSize);
    aNew[ii].bTruncateOnRelease = 1;
    if( !aNew[ii].pInSavepoint ){
      return SQLITE_NOMEM_BKPT;
    }
    if( pagerUseWal(pPager) ){
      sqlite3WalSavepoint(pPager->pWal, aNew[ii].aWalData);
    }
    pPager->nSavepoint = ii+1;

      sqlite3BitvecDestroy(pPager->aSavepoint[ii].pInSavepoint);
    }
    pPager->nSavepoint = nNew;

    /* If this is a release of the outermost savepoint, truncate 
    ** the sub-journal to zero bytes in size. */
    if( op==SAVEPOINT_RELEASE ){
      PagerSavepoint *pRel = &pPager->aSavepoint[nNew];
      if( pRel->bTruncateOnRelease && isOpen(pPager->sjfd) ){
        /* Only truncate if it is an in-memory sub-journal. */
        if( sqlite3JournalIsInMemory(pPager->sjfd) ){
          i64 sz = (pPager->pageSize+4)*pRel->iSubRec;
          rc = sqlite3OsTruncate(pPager->sjfd, sz);
          assert( rc==SQLITE_OK );
        }
        pPager->nSubRec = pRel->iSubRec;
      }
    }
    /* Else this is a rollback operation, playback the specified savepoint.
    ** If this is a temp-file, it is possible that the journal file has
    ** not yet been opened. In this case there have been no changes to
    ** the database file, so the playback operation can be skipped.
    */