Manual:Profiling/en

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Profiling tracks code execution during a page action and reports back the percentage of total code execution that was spent in any specific function. Profiling is an advanced task intended for developers and system administrators to track sources of slowness in MediaWiki that should be optimized.

PHP profiling

You can use Tideways or XDebug. These PHP extensions provide tracing and profiling capabilities.

Tideways also advertises a proprietary UI to visualize results, but you don't need that.

Install the php-tideways package on Debian/Ubuntu, or Homebrew on macOS.

For XDebug, see XDebug profiling documentation. For command line scripts, you can use php -d xdebug.mode=profile maintenance/{script}. Webgrind can then be used to view profile results.

MediaWiki custom profiler

The custom MediaWiki profiling calls (wfProfileIn/wfProfileOut) are deprecated, were no-ops since MediaWiki 1.25+, and were removed in 1.31.
MediaWiki version:
<translate> ≥</translate> 1.25

In MediaWiki 1.25 profiling was completely rewritten and many settings previous relating to profiling were removed in favor of consolidating them as parameters to $wgProfiler. Notably, output has been separated from class types. For documentation about profiling prior to 1.25, see an older version of this page.

Example $wgProfiler configuration: 

<?php
$wgProfiler['class'] = 'ProfilerXhprof';
$wgProfiler['output'] = [ 'ProfilerOutputText' ];
$wgProfiler['visible'] = true;

Each of these parameters (and more) are described in detail:

class
'ProfilerXhprof'. ProfilerXhprof is new in MediaWiki 1.25 and provides an Xhprof-backed profiler that captures profiling data for all functions as well as sub-functional units. Old values such as ProfilerStandard, ProfilerUDP, ProfilerDB, etc do not work. Even if you are using Tideways, still specify the ProfilerXhprof class.
output
One or more of 'ProfilerOutputText', 'ProfilerOutputDump', 'ProfilerOutputStats'[1]. Text outputs the information in either HTML comments or after the skin. UDP is a format send to a udpprofile daemon. Dump produces a dump of the profiling info for use with xhprof GUI (xhprofgui role on Vagrant setup).
outputDir
Only applies to 'ProfilerOutputDump' format. Required to specify where the dump files will be stored.
visible
Only applies to 'ProfilerOutputText' format. Whether text is shown after the skin or in an HTML comment.

Maintenance scripts

Maintenance scripts support a --profiler option. This changes the output method of the profiler as well as ensuring its enabled in the CLI. Because this only changes the output method and not the profiler class, you still must have some sort of profiling setup in $wgProfiler.


Troubleshooting

If you get "Fatal error: Uncaught Exception: Neither xhprof nor tideways are installed" then you need to do: 

$ sudo apt install php-tideways
$ sudo service apache2 restart

If you still get an error, then take a look at https://tideways.com/profiler/xhprof-for-php7

Output

Text output looks like: 

100.00% 508.972      1 - main()
 96.67% 492.003      1 - MediaWiki::run
 96.61% 491.699      1 - MediaWiki::main
 87.12% 443.434      1 - MediaWiki::performRequest
 84.16% 428.356      1 - SpecialPageFactory::executePath
 84.11% 428.073      1 - SpecialPage::run
 84.10% 428.058      1 - SpecialRecentChanges::execute
 63.82% 324.838      1 - ChangesListSpecialPage::execute
 57.07% 290.495      1 - ChangesListSpecialPage::webOutput
 51.06% 259.877      1 - SpecialRecentChanges::outputChangesList
 44.72% 227.633    397 - Wikimedia\Rdbms\Database::query
 31.07% 158.155    922 - Message::fetchMessage
 30.61% 155.788    865 - MessageCache::get
 29.55% 150.398    398 - Wikimedia\Rdbms\Database::doProfiledQuery
 29.39% 149.570    865 - MessageCache::getMessageFromFallbackChain
 29.26% 148.923    869 - MessageCache::getMessageForLang
 29.06% 147.931    393 - Wikimedia\Rdbms\Database::select
 27.30% 138.962      1 - EnhancedChangesList::endRecentChangesList
 27.30% 138.960      1 - EnhancedChangesList::recentChangesBlock
...

The first column is the time percent; the second column is the time (in ms); the third column is the count; and the fourth column is the name of the method.

See also

Footnotes

  1. ↑ See git #750e4eb9

Code steward

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