Incident documentation/20170124-WikibaseClient-InterwikiSorting

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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

Actionables

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