TLDR: If you use $wgDebugLogGroups['profileoutput'] in LocalSettings.php as a way to collect performance profiles from Tideways/XHProf, this will no longer receive messages in MediaWiki 1.35 and later.
-------
Hi,
I've been auditing the Profiler component in MediaWiki and deprecating or removing various legacy features that either don't fit the current model very well and/or that seem to be broken, unused or undocumented. [1] The objective here is to keep offering the same functionalities for developers, but in a way that's easier to use, with fewer moving parts, and lower maintenance costs for us.
Today I'm writing about the "profileoutput" debug log channel. As part of the PSR-3/Monolog refactor many years ago, this feature was grandfathered into the LegacyLogger.
The $wgProfiler variable controls which collector and output are used at run-time. For example, you can collect the call graph with XHProf/Tideways, and then output it to an HTML comment, or dump to a file on disk, etc. Any number of outputs can be implemented and enabled.
The "profileoutput" debug log channel was effectively another way of achieving the same thing, by assigning $wgDebugLogGroups['profileoutput'] to a file path.
If you're currently using this, see https://phabricator.wikimedia.org/T245835 for how to make this work via $wgProfiler instead.
-- Timo
wikitech-l@lists.wikimedia.org