Bug #79211 [NEW]: DomXPath::query() has very inconsistent performance

From: tom at r dot je Operating system: Linux PHP version: 7.4.2 Package: DOM XML related Bug Type: Bug Bug description:DomXPath::query() has very inconsistent performance Description: ------------ Here are three sample queries Equivalent of the CSS tr td.one //tr//td[contains(concat(\' \', normalize-space(@class), \' \'), \' one \')] Equivalent of the CSS td.one //td[contains(concat(\' \', normalize-space(@class), \' \'), \' one \')] Equivalent of the CSS tr td //tr//td There's a test script below that uses these queries on a 1000x6 HTML table. I'd expect them all to take roughly the same amount of time to run. Test script: --------------- <?php $xml = '<table>'; for ($i = 0; $i < 1000; $i++) { $xml .= '<tr><td class="one">A</td><td class="two">B</td><td class="three">C</td><td class="four">D</td><td class="five">E</td><td class="six">F</td> </tr>'; } $xml .= '</table>'; $doc = new \DomDocument; $doc->loadXml($xml); $xpath = new \DomXpath($doc); $t1 = microtime(true); // tr td.one $xpath->query('//tr//td[contains(concat(\' \', normalize-space(@class), \' \'), \' one \')]'); $t2 = microtime(true); echo '<p>tr td.one: ' . ($t2 - $t1) . '</p>'; $t1 = microtime(true); // td.one $xpath->query('//td[contains(concat(\' \', normalize-space(@class), \' \'), \' one \')]'); $t2 = microtime(true); echo '<p>td.one: ' . ($t2 - $t1) . '</p>'; $t1 = microtime(true); // tr td $xpath->query('//tr//td'); $t2 = microtime(true); echo '<p>tr td: ' . ($t2 - $t1) . '</p>'; Expected result: ---------------- While I'd expect some variation in speed, the first expression seems unreasonably slow in comparison to the others. Actual result: -------------- tr td.one: 0.26365518569946 td.one: 0.0054380893707275 tr td: 0.00074887275695801 Finding all td elements by class name is fast Finding all td elements inside a td is fast Combining those, finding all td elements by class inside a tr is 50 times slower than just finding all td elements by class. Since the first expression is a combination of the other two, how can it be 50 times slower? It's clearly not the concat and normalize-space functions that are slowing it down because the second expression is fine. -- Edit bug report at https://bugs.php.net/bug.php?id=79211&edit=1 -- Fix committed: https://bugs.php.net/fix.php?id=79211&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=79211&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=79211&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=79211&r=needscript Try newer version: https://bugs.php.net/fix.php?id=79211&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=79211&r=support Expected behavior: https://bugs.php.net/fix.php?id=79211&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=79211&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=79211&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=79211&r=globals PHP version support discontinued: https://bugs.php.net/fix.php?id=79211&r=phptooold Daylight Savings: https://bugs.php.net/fix.php?id=79211&r=dst IIS Stability: https://bugs.php.net/fix.php?id=79211&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=79211&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=79211&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=79211&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=79211&r=mysqlcfg