SQLite

/*
** 2004 April 6
**
** 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.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.555 2009/01/02 21:08:09 drh Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

  ** page size used by the pager associated with B-Tree pTo.
  **
  ** For example, say the page-size of pTo is 2048 bytes and the original 
  ** number of pages is 5 (10 KB file). If pFrom has a page size of 1024 
  ** bytes and 9 pages, then the file needs to be truncated to 9KB.
  */
  if( rc==SQLITE_OK ){
    if( nFromPageSize!=nToPageSize ){
      sqlite3_file *pFile = sqlite3PagerFile(pBtTo->pPager);
      i64 iSize = (i64)nFromPageSize * (i64)nFromPage;
      i64 iNow = (i64)((nToPage>nNewPage)?nToPage:nNewPage) * (i64)nToPageSize; 
      i64 iPending = ((i64)PENDING_BYTE_PAGE(pBtTo)-1) *(i64)nToPageSize;
  
      assert( iSize<=iNow );
  
      /* Commit phase one syncs the journal file associated with pTo 
      ** containing the original data. It does not sync the database file
      ** itself. After doing this it is safe to use OsTruncate() and other
      ** file APIs on the database file directly.
      */
      pBtTo->db = pTo->db;
      rc = sqlite3PagerCommitPhaseOne(pBtTo->pPager, 0, 1);
      if( iSize<iNow && rc==SQLITE_OK ){
        rc = sqlite3OsTruncate(pFile, iSize);
      }
  
      /* The loop that copied data from database pFrom to pTo did not
      ** populate the locking page of database pTo. If the page-size of
      ** pFrom is smaller than that of pTo, this means some data will
      ** not have been copied. 
      **
      ** This block copies the missing data from database pFrom to pTo 
      ** using file APIs. This is safe because at this point we know that
      ** all of the original data from pTo has been synced into the 
      ** journal file. At this point it would be safe to do anything at
      ** all to the database file except truncate it to zero bytes.
      */
      if( rc==SQLITE_OK && nFromPageSize<nToPageSize && iSize>iPending){
        i64 iOff;
        for(
          iOff=iPending; 
          rc==SQLITE_OK && iOff<(iPending+nToPageSize); 
          iOff += nFromPageSize
        ){
          DbPage *pFromPage = 0;
          Pgno iFrom = (Pgno)(iOff/nFromPageSize)+1;
  
          if( iFrom==PENDING_BYTE_PAGE(pBtFrom) || iFrom>nFromPage ){
            continue;
          }
  
          rc = sqlite3PagerGet(pBtFrom->pPager, iFrom, &pFromPage);
          if( rc==SQLITE_OK ){
            char *zFrom = sqlite3PagerGetData(pFromPage);
            rc = sqlite3OsWrite(pFile, zFrom, nFromPageSize, iOff);
            sqlite3PagerUnref(pFromPage);
          }
        }
      }
  

      /* Sync the database file */
      if( rc==SQLITE_OK ){
        rc = sqlite3PagerSync(pBtTo->pPager);
      }
    }else{
      rc = sqlite3PagerTruncate(pBtTo->pPager, nNewPage);
    }
    if( rc==SQLITE_OK ){
      pBtTo->pageSizeFixed = 0;
    }
  }

  if( rc ){
    sqlite3BtreeRollback(pTo);
  }

  return rc;  
}
int sqlite3BtreeCopyFile(Btree *pTo, Btree *pFrom){
  int rc;
  sqlite3BtreeEnter(pTo);
  sqlite3BtreeEnter(pFrom);
  rc = btreeCopyFile(pTo, pFrom);
  sqlite3BtreeLeave(pFrom);