Try waiting a few minutes and reloading.
(Cannot access the database)
Backtrace:
#0 /var/www/html/mediawiki/includes/libs/rdbms/database/DatabaseMysqlBase.php(142): Wikimedia\Rdbms\Database->newExceptionAfterConnectError()
#1 /var/www/html/mediawiki/includes/libs/rdbms/database/Database.php(326): Wikimedia\Rdbms\DatabaseMysqlBase->open()
#2 /var/www/html/mediawiki/includes/libs/rdbms/database/Database.php(310): Wikimedia\Rdbms\Database->doInitConnection()
#3 /var/www/html/mediawiki/includes/libs/rdbms/database/Database.php(435): Wikimedia\Rdbms\Database->initConnection()
#4 /var/www/html/mediawiki/extensions/Cargo/includes/CargoUtils.php(82): Wikimedia\Rdbms\Database::factory()
#5 /var/www/html/mediawiki/extensions/Cargo/includes/parserfunctions/CargoStore.php(113): CargoUtils::getDB()
#6 /var/www/html/mediawiki/includes/parser/Parser.php(3340): CargoStore::run()
#7 /var/www/html/mediawiki/includes/parser/Parser.php(3047): Parser->callParserFunction()
#8 /var/www/html/mediawiki/includes/parser/PPFrame_Hash.php(263): Parser->braceSubstitution()
#9 /var/www/html/mediawiki/extensions/ParserFunctions/includes/ParserFunctions.php(121): PPFrame_Hash->expand()
#10 /var/www/html/mediawiki/includes/parser/Parser.php(3340): MediaWiki\Extensions\ParserFunctions\ParserFunctions::if()
#11 /var/www/html/mediawiki/includes/parser/Parser.php(3047): Parser->callParserFunction()
#12 /var/www/html/mediawiki/includes/parser/PPFrame_Hash.php(263): Parser->braceSubstitution()
#13 /var/www/html/mediawiki/includes/parser/Parser.php(3225): PPFrame_Hash->expand()
#14 /var/www/html/mediawiki/includes/parser/PPFrame_Hash.php(263): Parser->braceSubstitution()
#15 /var/www/html/mediawiki/includes/parser/Parser.php(3225): PPFrame_Hash->expand()
#16 /var/www/html/mediawiki/includes/parser/PPFrame_Hash.php(263): Parser->braceSubstitution()
#17 /var/www/html/mediawiki/includes/parser/Parser.php(3331): PPFrame_Hash->expand()
#18 /var/www/html/mediawiki/includes/parser/Parser.php(3047): Parser->callParserFunction()
#19 /var/www/html/mediawiki/includes/parser/PPFrame_Hash.php(263): Parser->braceSubstitution()
#20 /var/www/html/mediawiki/includes/parser/Parser.php(3225): PPFrame_Hash->expand()
#21 /var/www/html/mediawiki/includes/parser/PPFrame_Hash.php(263): Parser->braceSubstitution()
#22 /var/www/html/mediawiki/includes/parser/Parser.php(2887): PPFrame_Hash->expand()
#23 /var/www/html/mediawiki/includes/parser/Parser.php(1556): Parser->replaceVariables()
#24 /var/www/html/mediawiki/includes/parser/Parser.php(651): Parser->internalParse()
#25 /var/www/html/mediawiki/includes/content/WikitextContent.php(374): Parser->parse()
#26 /var/www/html/mediawiki/includes/content/AbstractContent.php(590): WikitextContent->fillParserOutput()
#27 /var/www/html/mediawiki/includes/Revision/RenderedRevision.php(263): AbstractContent->getParserOutput()
#28 /var/www/html/mediawiki/includes/Revision/RenderedRevision.php(235): MediaWiki\Revision\RenderedRevision->getSlotParserOutputUncached()
#29 /var/www/html/mediawiki/includes/Revision/RevisionRenderer.php(215): MediaWiki\Revision\RenderedRevision->getSlotParserOutput()
#30 /var/www/html/mediawiki/includes/Revision/RevisionRenderer.php(152): MediaWiki\Revision\RevisionRenderer->combineSlotOutput()
#31 [internal function]: MediaWiki\Revision\RevisionRenderer->MediaWiki\Revision\{closure}()
#32 /var/www/html/mediawiki/includes/Revision/RenderedRevision.php(197): call_user_func()
#33 /var/www/html/mediawiki/includes/poolcounter/PoolWorkArticleView.php(216): MediaWiki\Revision\RenderedRevision->getRevisionParserOutput()
#34 /var/www/html/mediawiki/includes/poolcounter/PoolCounterWork.php(162): PoolWorkArticleView->doWork()
#35 /var/www/html/mediawiki/includes/page/WikiPage.php(1281): PoolCounterWork->execute()
#36 /var/www/html/mediawiki/includes/diff/DifferenceEngine.php(1093): WikiPage->getParserOutput()
#37 /var/www/html/mediawiki/includes/diff/DifferenceEngine.php(1050): DifferenceEngine->getParserOutput()
#38 /var/www/html/mediawiki/includes/diff/DifferenceEngine.php(878): DifferenceEngine->renderNewRevision()
#39 /var/www/html/mediawiki/includes/page/Article.php(980): DifferenceEngine->showDiffPage()
#40 /var/www/html/mediawiki/includes/page/Article.php(656): Article->showDiffPage()
#41 /var/www/html/mediawiki/includes/actions/ViewAction.php(80): Article->view()
#42 /var/www/html/mediawiki/includes/MediaWiki.php(532): ViewAction->show()
#43 /var/www/html/mediawiki/includes/MediaWiki.php(313): MediaWiki->performAction()
#44 /var/www/html/mediawiki/includes/MediaWiki.php(945): MediaWiki->performRequest()
#45 /var/www/html/mediawiki/includes/MediaWiki.php(548): MediaWiki->main()
#46 /var/www/html/mediawiki/index.php(53): MediaWiki->run()
#47 /var/www/html/mediawiki/index.php(46): wfIndexMain()
#48 {main}