From Adrian Lang's email to wikitech-l http://www.gossamer-threads.com/lists/wiki/wikitech/452196:

I recently investigated a performance issue with one of Wikibase's
test cases. The test in question performed a formatting task for all
known languages. While the first assertions ran as fast as expected,
they rapidly got slower until finally taking seconds per assertion. I
figured this was an actual performance bug (although hardly triggered
in production) and started profiling.

My findings, in short:

• The shims for $wgExtensionMessagesFiles as generated by

maintenance/generateJsonI18n.php register a handler for the hook
LocalisationCacheRecache when included

• For every new language loaded, all $wgExtensionMessagesFiles are

included by LocalisationCache::recache

• Afterwards, LocalisationCache::recache runs the hook LocalisationCacheRecache

This leads to the obvious issue that there is a growing number of
registered handlers, which slows down the hook, which slows down the
test.

The shims should be fixed to avoid this.

Version: 1.23.0
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=63926