MediaWiki internal error.

Original exception: [5efe7944ba60552078367674] /wiki/Item:Q4725143 Wikimedia\Rdbms\DBQueryDisconnectedError: A database query error has occurred. Did you forget to run your application's database schema updater after upgrading or after adding a new extension?

Please see https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:Upgrading and https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:How_to_debug for more information.

A connection error occurred during a query.
Query: SELECT page_id,page_namespace,page_title,page_is_redirect,page_is_new,page_latest,page_touched,page_len,page_content_model FROM `page` WHERE ((page_namespace = 122 AND page_title IN ('P31','P225','P16','P28','P226','P1451','P1450','P1460') ) OR (page_namespace = 120 AND page_title IN ('Q56887','Q441094','Q3763958','Q1104483','Q5976449') ))
Function: MediaWiki\Cache\LinkBatch::doQuery (for Wikibase\Repo\ParserOutput\ReferencedEntitiesDataUpdater::addLinksToParserOutput)
Error: 2006 MySQL server has gone away

Backtrace:
from /var/www/html/w/includes/libs/rdbms/database/Database.php(1228)
#0 /var/www/html/w/includes/libs/rdbms/database/Database.php(1214): Wikimedia\Rdbms\Database->getQueryException(string, int, string, string)
#1 /var/www/html/w/includes/libs/rdbms/database/Database.php(1188): Wikimedia\Rdbms\Database->getQueryExceptionAndLog(string, int, string, string)
#2 /var/www/html/w/includes/libs/rdbms/database/Database.php(647): Wikimedia\Rdbms\Database->reportQueryError(string, int, string, string, bool)
#3 /var/www/html/w/includes/libs/rdbms/database/Database.php(1365): Wikimedia\Rdbms\Database->query(Wikimedia\Rdbms\Query, string)
#4 /var/www/html/w/includes/libs/rdbms/database/DBConnRef.php(127): Wikimedia\Rdbms\Database->select(array, array, array, string, array, array)
#5 /var/www/html/w/includes/libs/rdbms/database/DBConnRef.php(351): Wikimedia\Rdbms\DBConnRef->__call(string, array)
#6 /var/www/html/w/includes/libs/rdbms/querybuilder/SelectQueryBuilder.php(762): Wikimedia\Rdbms\DBConnRef->select(array, array, array, string, array, array)
#7 /var/www/html/w/includes/cache/LinkBatch.php(341): Wikimedia\Rdbms\SelectQueryBuilder->fetchResultSet()
#8 /var/www/html/w/extensions/Wikibase/repo/includes/ParserOutput/ReferencedEntitiesDataUpdater.php(66): MediaWiki\Cache\LinkBatch->doQuery()
#9 /var/www/html/w/extensions/Wikibase/repo/includes/ParserOutput/ReferencedEntitiesDataUpdater.php(55): Wikibase\Repo\ParserOutput\ReferencedEntitiesDataUpdater->addLinksToParserOutput(MediaWiki\Parser\ParserOutput, array)
#10 /var/www/html/w/extensions/Wikibase/repo/includes/ParserOutput/EntityParserOutputDataUpdaterCollection.php(44): Wikibase\Repo\ParserOutput\ReferencedEntitiesDataUpdater->updateParserOutput(MediaWiki\Parser\ParserOutput, Wikibase\DataModel\Entity\Item)
#11 /var/www/html/w/extensions/Wikibase/repo/includes/ParserOutput/FullEntityParserOutputGenerator.php(91): Wikibase\Repo\ParserOutput\EntityParserOutputDataUpdaterCollection->updateParserOutput(Wikibase\DataModel\Entity\Item)
#12 /var/www/html/w/extensions/Wikibase/repo/includes/ParserOutput/StatsdTimeRecordingEntityParserOutputGenerator.php(53): Wikibase\Repo\ParserOutput\FullEntityParserOutputGenerator->getParserOutput(Wikibase\Lib\Store\EntityRevision, bool)
#13 /var/www/html/w/extensions/Wikibase/repo/includes/Content/EntityHandler.php(861): Wikibase\Repo\ParserOutput\StatsdTimeRecordingEntityParserOutputGenerator->getParserOutput(Wikibase\Lib\Store\EntityRevision, bool)
#14 /var/www/html/w/extensions/Wikibase/repo/includes/Content/ItemHandler.php(302): Wikibase\Repo\Content\EntityHandler->getParserOutputFromEntityView(Wikibase\Repo\Content\ItemContent, int, MediaWiki\Parser\ParserOptions, bool)
#15 /var/www/html/w/extensions/Wikibase/repo/includes/Content/EntityHandler.php(790): Wikibase\Repo\Content\ItemHandler->getParserOutputFromEntityView(Wikibase\Repo\Content\ItemContent, int, MediaWiki\Parser\ParserOptions, bool)
#16 /var/www/html/w/includes/content/ContentHandler.php(1697): Wikibase\Repo\Content\EntityHandler->fillParserOutput(Wikibase\Repo\Content\ItemContent, MediaWiki\Content\Renderer\ContentParseParams, MediaWiki\Parser\ParserOutput)
#17 /var/www/html/w/includes/content/Renderer/ContentRenderer.php(75): MediaWiki\Content\ContentHandler->getParserOutput(Wikibase\Repo\Content\ItemContent, MediaWiki\Content\Renderer\ContentParseParams)
#18 /var/www/html/w/includes/Revision/RenderedRevision.php(261): MediaWiki\Content\Renderer\ContentRenderer->getParserOutput(Wikibase\Repo\Content\ItemContent, MediaWiki\Page\PageIdentityValue, MediaWiki\Revision\RevisionStoreRecord, MediaWiki\Parser\ParserOptions, array)
#19 /var/www/html/w/includes/Revision/RenderedRevision.php(233): MediaWiki\Revision\RenderedRevision->getSlotParserOutputUncached(Wikibase\Repo\Content\ItemContent, array)
#20 /var/www/html/w/includes/Revision/RevisionRenderer.php(236): MediaWiki\Revision\RenderedRevision->getSlotParserOutput(string, array)
#21 /var/www/html/w/includes/Revision/RevisionRenderer.php(169): MediaWiki\Revision\RevisionRenderer->combineSlotOutput(MediaWiki\Revision\RenderedRevision, MediaWiki\Parser\ParserOptions, array)
#22 [internal function]: MediaWiki\Revision\RevisionRenderer->MediaWiki\Revision\{closure}(MediaWiki\Revision\RenderedRevision, array)
#23 /var/www/html/w/includes/Revision/RenderedRevision.php(196): call_user_func(Closure, MediaWiki\Revision\RenderedRevision, array)
#24 /var/www/html/w/includes/poolcounter/PoolWorkArticleView.php(106): MediaWiki\Revision\RenderedRevision->getRevisionParserOutput()
#25 /var/www/html/w/includes/poolcounter/PoolWorkArticleViewCurrent.php(123): MediaWiki\PoolCounter\PoolWorkArticleView->renderRevision(null, bool, string)
#26 /var/www/html/w/includes/poolcounter/PoolCounterWork.php(171): MediaWiki\PoolCounter\PoolWorkArticleViewCurrent->doWork()
#27 /var/www/html/w/includes/page/ParserOutputAccess.php(369): MediaWiki\PoolCounter\PoolCounterWork->execute()
#28 /var/www/html/w/includes/page/Article.php(829): MediaWiki\Page\ParserOutputAccess->getParserOutput(WikiPage, MediaWiki\Parser\ParserOptions, MediaWiki\Revision\RevisionStoreRecord, int)
#29 /var/www/html/w/includes/page/Article.php(545): Article->generateContentOutput(MediaWiki\User\User, MediaWiki\Parser\ParserOptions, int, MediaWiki\Output\OutputPage, array)
#30 /var/www/html/w/extensions/Wikibase/repo/includes/Actions/ViewEntityAction.php(80): Article->view()
#31 /var/www/html/w/extensions/Wikibase/repo/includes/Actions/ViewEntityAction.php(55): Wikibase\Repo\Actions\ViewEntityAction->showEntityPage()
#32 /var/www/html/w/includes/actions/ActionEntryPoint.php(732): Wikibase\Repo\Actions\ViewEntityAction->show()
#33 /var/www/html/w/includes/actions/ActionEntryPoint.php(509): MediaWiki\Actions\ActionEntryPoint->performAction(Article, MediaWiki\Title\Title)
#34 /var/www/html/w/includes/actions/ActionEntryPoint.php(145): MediaWiki\Actions\ActionEntryPoint->performRequest()
#35 /var/www/html/w/includes/MediaWikiEntryPoint.php(202): MediaWiki\Actions\ActionEntryPoint->execute()
#36 /var/www/html/w/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#37 {main}

Exception caught inside exception handler: [5efe7944ba60552078367674] /wiki/Item:Q4725143 Wikimedia\Rdbms\DBConnectionError: Cannot access the database: Connection refused (mysql.svc:3306)
Backtrace:
from /var/www/html/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php(1131)
#0 /var/www/html/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php(821): Wikimedia\Rdbms\LoadBalancer->reportConnectionError()
#1 /var/www/html/w/includes/libs/rdbms/loadbalancer/LoadBalancer.php(788): Wikimedia\Rdbms\LoadBalancer->getServerConnection(int, string, int)
#2 /var/www/html/w/includes/libs/rdbms/database/DBConnRef.php(111): Wikimedia\Rdbms\LoadBalancer->getConnectionInternal(int, array, string, int)
#3 /var/www/html/w/includes/libs/rdbms/database/DBConnRef.php(125): Wikimedia\Rdbms\DBConnRef->ensureConnection()
#4 /var/www/html/w/includes/libs/rdbms/database/DBConnRef.php(351): Wikimedia\Rdbms\DBConnRef->__call(string, array)
#5 /var/www/html/w/includes/libs/rdbms/querybuilder/SelectQueryBuilder.php(762): Wikimedia\Rdbms\DBConnRef->select(array, array, array, string, array, array)
#6 /var/www/html/w/includes/page/PageProps.php(118): Wikimedia\Rdbms\SelectQueryBuilder->fetchResultSet()
#7 /var/www/html/w/extensions/DisplayTitle/includes/DisplayTitleService.php(204): MediaWiki\Page\PageProps->getProperties(MediaWiki\Title\Title, array)
#8 /var/www/html/w/extensions/DisplayTitle/includes/DisplayTitleService.php(239): MediaWiki\Extension\DisplayTitle\DisplayTitleService->getDisplayTitle(MediaWiki\Title\Title, null)
#9 /var/www/html/w/extensions/DisplayTitle/includes/DisplayTitleHooks.php(169): MediaWiki\Extension\DisplayTitle\DisplayTitleService->setSubtitle(MediaWiki\Output\OutputPage)
#10 /var/www/html/w/includes/HookContainer/HookContainer.php(155): MediaWiki\Extension\DisplayTitle\DisplayTitleHooks->onBeforePageDisplay(MediaWiki\Output\OutputPage, Skins\Chameleon\Chameleon)
#11 /var/www/html/w/includes/HookContainer/HookRunner.php(992): MediaWiki\HookContainer\HookContainer->run(string, array, array)
#12 /var/www/html/w/includes/Output/OutputPage.php(3187): MediaWiki\HookContainer\HookRunner->onBeforePageDisplay(MediaWiki\Output\OutputPage, Skins\Chameleon\Chameleon)
#13 /var/www/html/w/includes/exception/MWExceptionRenderer.php(189): MediaWiki\Output\OutputPage->output()
#14 /var/www/html/w/includes/exception/MWExceptionRenderer.php(110): MWExceptionRenderer::reportHTML(Wikimedia\Rdbms\DBQueryDisconnectedError)
#15 /var/www/html/w/includes/exception/MWExceptionHandler.php(134): MWExceptionRenderer::output(Wikimedia\Rdbms\DBQueryDisconnectedError, int)
#16 /var/www/html/w/includes/exception/MWExceptionHandler.php(238): MWExceptionHandler::report(Wikimedia\Rdbms\DBQueryDisconnectedError)
#17 /var/www/html/w/includes/MediaWikiEntryPoint.php(222): MWExceptionHandler::handleException(Wikimedia\Rdbms\DBQueryDisconnectedError, string)
#18 /var/www/html/w/includes/actions/ActionEntryPoint.php(81): MediaWiki\MediaWikiEntryPoint->handleTopLevelError(Wikimedia\Rdbms\DBQueryDisconnectedError)
#19 /var/www/html/w/includes/MediaWikiEntryPoint.php(208): MediaWiki\Actions\ActionEntryPoint->handleTopLevelError(Wikimedia\Rdbms\DBQueryDisconnectedError)
#20 /var/www/html/w/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#21 {main}