function _load_tree_nodes($poff)
	{
		fseek($this->fd, $poff, SEEK_SET);
		$buf = fread($this->fd, 8);
		if (strlen($buf) != 8) return;

		$tmp = unpack('Ioff/Ilen', $buf);
		if ($tmp['len'] == 0) return;
		fseek($this->fd, $tmp['off'], SEEK_SET);

		$rlen = XDB_MAXKLEN + 17;
		if ($rlen > $tmp['len']) $rlen = $tmp['len'];
		$buf = fread($this->fd, $rlen);

		$rec = unpack('Iloff/Illen/Iroff/Irlen/Cklen', substr($buf, 0, 17));
		$rec['off'] = $tmp['off'];
		$rec['len'] = $tmp['len'];
		$rec['key'] = substr($buf, 17, $rec['klen']);
		$this->_sync_nodes[] = $rec;
		unset($buf);

		// left
		if ($rec['llen'] != 0) $this->_load_tree_nodes($tmp['off']);
		// right
		if ($rec['rlen'] != 0) $this->_load_tree_nodes($tmp['off'] + 8);
	}