function _reset_tree_nodes($poff, $low, $high)
	{
		if ($low <= $high)
		{
			$mid = ($low+$high)>>1;
			$node = $this->_sync_nodes[$mid];
			$buf = pack('II', $node['off'], $node['len']);

			// left
			$this->_reset_tree_nodes($node['off'], $low, $mid - 1);
			// right
			$this->_reset_tree_nodes($node['off'] + 8, $mid + 1, $high);
		}
		else
		{
			$buf = pack('II', 0, 0);
		}

		fseek($this->fd, $poff, SEEK_SET);
		fwrite($this->fd, $buf, 8);
	}