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Parsing document with a lot of HTML tags is slow #181

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alecpl opened this issue Apr 16, 2020 · 12 comments
Open

Parsing document with a lot of HTML tags is slow #181

alecpl opened this issue Apr 16, 2020 · 12 comments

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@alecpl
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alecpl commented Apr 16, 2020

I have a script that generates a HTML sample that is ~1.5MB in size. It emulates a real-world example. Then I parse it.

$html = '<HTML><BODY>';
$lines = 20000;
while ($lines--) {
    $html .= '<P DIR=LTR><SPAN LANG="en-gb"><FONT FACE="Consolas">&gt;&gt; </FONT></SPAN></P>';
}

$html5 = new Masterminds\HTML5();
$node  = $html5->loadHTML($html);

and here's the result:

PHP Fatal error:  Maximum execution time of 120 seconds exceeded in vendor/masterminds/html5/src/HTML5/Parser/DOMTreeBuilder.php on line 433
PHP Stack trace:
PHP   1. {main}() test.php:0
PHP   2. Masterminds\HTML5->loadHTML() test.php:23
PHP   3. Masterminds\HTML5->parse() vendor/masterminds/html5/src/HTML5.php:98
PHP   4. Masterminds\HTML5\Parser\Tokenizer->parse() vendor/masterminds/html5/src/HTML5.php:174
PHP   5. Masterminds\HTML5\Parser\Tokenizer->consumeData() vendor/masterminds/html5/src/HTML5/Parser/Tokenizer.php:89
PHP   6. Masterminds\HTML5\Parser\Tokenizer->tagOpen() vendor/masterminds/html5/src/HTML5/Parser/Tokenizer.php:132
PHP   7. Masterminds\HTML5\Parser\Tokenizer->tagName() vendor/masterminds/html5/src/HTML5/Parser/Tokenizer.php:284
PHP   8. Masterminds\HTML5\Parser\DOMTreeBuilder->startTag() vendor/masterminds/html5/src/HTML5/Parser/Tokenizer.php:388

I tested this with 2.7.0 and some older versions with no success. The sample half of that size works, but it takes 27 seconds to finish (so it's not linear).

Cross-ref: roundcube/roundcubemail#7331
@goetas
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goetas commented Apr 18, 2020

Have you tried to debug it with backfire or some other profiler?

@alecpl
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alecpl commented Apr 18, 2020

I didn't yet, but I can add that the specific content is not that important, the number of tags is. So, it looks like this library has problem with parsing big HTML pages. FYI, DOMDocument parses the sample in less than a second.

@alecpl
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alecpl commented Apr 18, 2020 •
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I'm not sure how useful is that, but here's xdebug profile on a smaller sample. Sorry, for Polish language, but forcing English in KCacheGrind didn't work.
xdebug

@alecpl alecpl changed the title Parsing specific (long) HTML content is too slow (infinite loop?) Parsing document with a lot of HTML tags is slow Apr 19, 2020
@alecpl
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alecpl commented Apr 19, 2020

So, it looks like a DOMElement::appendChild() is the main bottleneck. Here's some performance stats showing how number of tags makes a difference. PHP 7.4.

Tags  |  Time
---------------
10k   |   1.3s
20k   |   3.3s
30k   |   7.9s
40k   |  16.4s
50k   |  28.3s

@alecpl alecpl mentioned this issue Apr 19, 2020
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@goetas
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goetas commented Apr 19, 2020

can you try to benchmark appendChild alone and see if that slows down after a certain number of tags?

@alecpl
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alecpl commented Apr 19, 2020 •
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Nope, and it's the other way round (more tags, better time per tag). What's more the following script is blazingly fast (<1sec).

$doc = new DOMDocument;
$body = $doc->createElement("body");
$doc->appendChild($body);
$lines = 100000;
while ($lines--) {
    $p = $doc->createElement("p");
    $body->appendChild($p);
    $span = $doc->createElement("span");
    $p->appendChild($span);
    $font = $doc->createElement("font");
    $span->appendChild($font);
}

@goetas
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goetas commented Apr 19, 2020

image

@goetas
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goetas commented Apr 19, 2020

Hmm, weird...

@goetas
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goetas commented Jun 14, 2020 •
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the bottleneck seems to be autoclose()..., by removing that, the script completes in 3s
NVM

@goetas
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goetas commented Jun 14, 2020 •
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This turned out to be a PHP issue that can be workedaroud by doing

$html5 = new Masterminds\HTML5([
    'disable_html_ns' => true
]);
$node  = $html5->loadHTML($html);

The perf issue was introduced by https://github.com/php/php-src/blob/35e0a91db717fe441a89ca9554d8843d8ee63112/ext/dom/php_dom.c and php/php-src@84b90f6

@alecpl
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alecpl commented Jul 26, 2020

Thanks for the workaround. With it my initial test script takes 8 seconds, not that bad. DOMDocument needs 0.3 second.

Did you already create a ticket in PHP's bugtracker?

@steinmb
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steinmb commented Feb 23, 2024

Was listed by xhprof with PHP 8.3.2-1. Is this a thing or should I look other places?

Screenshot 2024-02-23 at 12 29 38

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@alecpl @steinmb @goetas