After we got MW installed (see T192965), MediaWiki wouldn't work. Visiting the page would end up with an error:
[c032b5a46de7da3a0ff9d8c9] 2018-04-24 20:06:51: Fatal exception of type Wikimedia\Rdbms\DBQueryError
on an otherwise empty page. Adding a debug log and we got the following as the last thing recorded:
[SQLBagOStuff] Duplicate get(): "DBNAME:messages:en" fetched 3 times
[SQLBagOStuff] Duplicate get(): "DBNAME:messages:en:status" fetched 3 times
[SQLBagOStuff] Duplicate get(): "DBNAME:messages:en:lock" fetched 3 times
[DBQuery] DBNAME SELECT /* LCStoreDB::get */ TOP 1 lc_value FROM [l10n_cache] WHERE lc_lang = 'en' AND lc_key = 'messages:title-invalid-empty'
[DBQuery] SQL ERROR: [SQLSTATE 42S02][Error Code 208][Microsoft][ODBC Driver 13 for SQL Server][SQL Server]Invalid object name 'l10n_cache'.
[SQLSTATE 42000][Error Code 8180][Microsoft][ODBC Driver 13 for SQL Server][SQL Server]Statement(s) could not be prepared.
[exception] [52606319bb248016995a2c8f] / Wikimedia\Rdbms\DBQueryError from line 1149 of C:...includes\libs\rdbms\database\Database.php: A database query error has occurred. Did you forget to run your application's database schema updater after upgrading?
Query: SELECT TOP 1 lc_value FROM [l10n_cache] WHERE lc_lang = 'en' AND lc_key = 'messages:title-invalid-empty'
Function: LCStoreDB::get
Error: 208 [SQLSTATE 42S02][Error Code 208][Microsoft][ODBC Driver 13 for SQL Server][SQL Server]Invalid object name 'l10n_cache'.
[SQLSTATE 42000][Error Code 8180][Microsoft][ODBC Driver 13 for SQL Server][SQL Server]Statement(s) could not be prepared.
#0 C:...includes\libs\rdbms\database\Database.php(979): Wikimedia\Rdbms\Database->reportQueryError(string, integer, string, string, boolean)
#1 C:...includes\libs\rdbms\database\DatabaseMssql.php(414): Wikimedia\Rdbms\Database->query(string, string)
#2 C:...includes\libs\rdbms\database\Database.php(1169): Wikimedia\Rdbms\DatabaseMssql->select(string, string, array, string, array, array)
#3 C:...includes\cache\localisation\LCStoreDB.php(52): Wikimedia\Rdbms\Database->selectField(string, string, array, string)
#4 C:...includes\cache\localisation\LocalisationCache.php(392): LCStoreDB->get(string, string)
#5 C:...includes\cache\localisation\LocalisationCache.php(291): LocalisationCache->loadSubitem(string, string, string)
#6 C:...languages\Language.php(2587): LocalisationCache->getSubitem(string, string, string)
#7 C:...includes\cache\MessageCache.php(933): Language->getMessage(string)
#8 C:...includes\cache\MessageCache.php(888): MessageCache->getMessageForLang(LanguageEn, string, boolean, array)
#9 C:...includes\cache\MessageCache.php(828): MessageCache->getMessageFromFallbackChain(LanguageEn, string, boolean)
#10 C:...includes\Message.php(1275): MessageCache->get(string, boolean, LanguageEn)
#11 C:...includes\Message.php(842): Message->fetchMessage()
#12 C:...includes\Message.php(934): Message->toString(string)
#13 C:...includes\title\MalformedTitleException.php(49): Message->text()
#14 C:...includes\title\MediaWikiTitleCodec.php(311): MalformedTitleException->__construct(string, string)
#15 C:...includes\Title.php(3526): MediaWikiTitleCodec->splitTitleString(string, integer)
#16 C:...includes\Title.php(361): Title->secureAndSplit()
#17 C:...includes\MediaWiki.php(84): Title::newFromURL(NULL)
#18 C:...includes\MediaWiki.php(140): MediaWiki->parseTitle()
#19 C:...includes\MediaWiki.php(920): MediaWiki->getTitle()
#20 C:...includes\MediaWiki.php(900): MediaWiki->triggerJobs()
#21 C:...includes\MediaWiki.php(719): MediaWiki->restInPeace(string, boolean)
#22 C:...includes\MediaWiki.php(740): MediaWiki->{closure}()
#23 C:...includes\MediaWiki.php(553): MediaWiki->doPostOutputShutdown(string)
#24 C:...index.php(43): MediaWiki->run()
#25 {main}
[session] Saving all sessions on shutdown
[DBConnection] Closing connection to database 'localhost'.
[DBConnection] Closing connection to database 'localhost'.