public void unpin(Block blk)
{//释放指定的block
Buffer buff = buffers[blk];
bufferMgr.unpin(buff);
pins.Remove(blk);
if (!pins.Contains(blk)) //当前pins里的这个block没有被其他缓冲区绑定的时候
{
buffers.Remove(blk); //就从字典里删除这个blk的所有信息
}
}
public override void undo(int txnum)
{
BufferMgr buffMgr = SimpleDB.bufferMgr();
Buffer buff = buffMgr.pin(blk);
buff.setString(offset, val, txnum, -1);
buffMgr.unpin(buff);
}
public override void undo(int txnum)
{
BufferMgr buffMgr = SimpleDB.bufferMgr();
//将块绑定到（读入）缓冲区
Buffer buff = buffMgr.pin(blk);
//LSN为负数，生成一条临时日志记录，不保存到磁盘
buff.setInt(offset, val, txnum, -1);
buffMgr.unpin(buff);
}