php读xml巨慢（大数据量）,该怎么处理

$file = "data.xml";<br />$depth = array();<br /><br />function startElement($parser, $name, $attrs)<br />{<br />    global $depth;<br />    for ($i = 0; $i < $depth[$parser]; $i++) {<br />        echo "  ";<br />    }<br />    echo "$name\n";<br />    $depth[$parser]++;<br />}<br /><br />function endElement($parser, $name)<br />{<br />    global $depth;<br />    $depth[$parser]--;<br />}<br /><br />$xml_parser = xml_parser_create();<br />xml_set_element_handler($xml_parser, "startElement", "endElement");<br />if (!($fp = fopen($file, "r"))) {<br />    die("could not open XML input");<br />}<br /><br />while ($data = fread($fp, 4096)) {<br />    if (!xml_parse($xml_parser, $data, feof($fp))) {<br />        die(sprintf("XML error: %s at line %d",<br />                    xml_error_string(xml_get_error_code($xml_parser)),<br />                    xml_get_current_line_number($xml_parser)));<br />    }<br />}<br />xml_parser_free($xml_parser);<br />