Try waiting a few minutes and reloading.
(Cannot access the database)
Backtrace:
#0 /mnt/iop/wiki/includes/libs/rdbms/loadbalancer/LoadBalancer.php(794): Wikimedia\Rdbms\LoadBalancer->reportConnectionError()
#1 /mnt/iop/wiki/includes/libs/rdbms/loadbalancer/LoadBalancer.php(782): Wikimedia\Rdbms\LoadBalancer->getServerConnection()
#2 /mnt/iop/wiki/includes/libs/rdbms/database/DBConnRef.php(99): Wikimedia\Rdbms\LoadBalancer->getConnectionInternal()
#3 /mnt/iop/wiki/includes/libs/rdbms/database/DBConnRef.php(117): Wikimedia\Rdbms\DBConnRef->ensureConnection()
#4 /mnt/iop/wiki/includes/libs/rdbms/database/DBConnRef.php(338): Wikimedia\Rdbms\DBConnRef->__call()
#5 /mnt/iop/wiki/includes/libs/rdbms/querybuilder/SelectQueryBuilder.php(747): Wikimedia\Rdbms\DBConnRef->selectField()
#6 /mnt/iop/wiki/includes/user/TalkPageNotificationManager.php(259): Wikimedia\Rdbms\SelectQueryBuilder->fetchField()
#7 /mnt/iop/wiki/includes/user/TalkPageNotificationManager.php(95): MediaWiki\User\TalkPageNotificationManager->dbCheckNewUserMessages()
#8 /mnt/iop/wiki/includes/cache/HTMLFileCache.php(130): MediaWiki\User\TalkPageNotificationManager->userHasNewMessages()
#9 /mnt/iop/wiki/includes/actions/ActionEntryPoint.php(71): HTMLFileCache::useFileCache()
#10 /mnt/iop/wiki/includes/MediaWikiEntryPoint.php(205): MediaWiki\Actions\ActionEntryPoint->handleTopLevelError()
#11 /mnt/iop/wiki/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#12 {main}