Incident documentation/2017-01-24 WikibaseClient-InterwikiSorting

Summary

Due to an automatic switch in WikibaseClient adding configuration for the InterwikiSorting extension caused Wikibase to start using it in production.

This wouldn't have been an issue, except WikibaseClient only checks for one setting but uses 4.

One of these settings no longer exists in the extension and was thus not included in the config change.

Fatals on all wikis using WikibaseClient for about 3 minutes where the parser cache was missed and getParserOutput was thus called.

Although mwdebug1002 was checked, the issue was not spotted, probably due to the issue only arising on getParserOutput calls, cached output would not expose the error.

Timeline

• 12:12 Copy InterwikiSorting settings from wmgWikibaseClientSettings merged by jenkins
• 12:13 addshore@mwdebug1002 scap pull
• 12:14 addshore@tin: Synchronized wmf-config/InitialiseSettings.php: T155995 Copy InterwikiSorting settings from wmgWikibaseClientSettings noop (duration: 00m 39s)
• 12:17 addshore@tin: Synchronized wmf-config/InitialiseSettings.php: Revert last (duration: 00m 39s)
• 12:19 Reported as https://phabricator.wikimedia.org/T156123
• 12:26 Revert "Copy InterwikiSorting settings from wmgWikibaseClientSettings" added to gerrit

Actionables

• Do not use wgInterwikiSortingAlwaysSort in WikibaseClient (bug T156128) 333932
• Check all config options used... 333933