Last modified: 2013-09-26 15:10:56 UTC
While CirrusSearch is doing a transparent reindex requests that span all namespaces hit both the old and the newly made index. This causes duplicate results and is otherwise silly. This is due to the new index grabbing the _wikiname_ alias before it is populated and without removing that alias from the old index.
Change 81866 had a related patch set uploaded by Chad: Carefully replace aliases to prevent duplicates. https://gerrit.wikimedia.org/r/81866
Change 81866 merged by jenkins-bot: Carefully replace aliases to prevent duplicates. https://gerrit.wikimedia.org/r/81866
Deployed and we haven't seen the problem since.