MediaWiki internal error.

Original exception: [a251dfaeaec1a3b422d2c468] /index.php?title=%25CE%2595%25CE%25B9%25CE%25B4%25CE%25B9%25CE%25BA%25CF%258C:%25CE%25A3%25CF%258D%25CE%25BD%25CE%25B4%25CE%25B5%25CF%2583%25CE%25B7%25CE%25A7%25CF%2581%25CE%25AE%25CF%2583%25CF%2584%25CE%25B7&returnto=%25CE%2591%25CE%25BB%25CE%25BB%25CE%25B1%25CE%25B3%25CE%25AE+%25CE%25B5%25CF%2580%25CF%2589%25CE%25BD%25CF%2585%25CE%25BC%25CE%25AF%25CE%25B1%25CF%2582+%25CE%25B2%25CE%25B9%25CE%25BF%25CF%2584%25CE%25B5%25CF%2587%25CE%25BD%25CE%25B9%25CE%25BA%25CE%25AE%25CF%2582+%25CE%25BC%25CE%25BF%25CE%25BD%25CE%25AC%25CE%25B4%25CE%25B1%25CF%2582&returntoquery=oldid%253D12655 Wikimedia\Rdbms\DBQueryError from line 1075 of /var/www/wiki.ellak.gr/pool.diadikasies.gr/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 page_id,page_len,page_is_redirect,page_latest,page_content_model FROM `page` WHERE page_namespace = '0' AND page_title = 'Αρχική_σελίδα' LIMIT 1
Function: LinkCache::fetchPageRow
Error: 2002 Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111) (localhost:3306)

Backtrace:
#0 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/libs/rdbms/database/Database.php(933): Wikimedia\Rdbms\Database->reportQueryError(string, integer, string, string, boolean)
#1 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/libs/rdbms/database/Database.php(1269): Wikimedia\Rdbms\Database->query(string, string)
#2 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/libs/rdbms/database/Database.php(1337): Wikimedia\Rdbms\Database->select(string, array, array, string, array, array)
#3 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/cache/LinkCache.php(313): Wikimedia\Rdbms\Database->selectRow(string, array, array, string)
#4 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/cache/LinkCache.php(270): LinkCache->fetchPageRow(Wikimedia\Rdbms\DatabaseMysqli, Title)
#5 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/Title.php(3233): LinkCache->addLinkObj(Title)
#6 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/Title.php(4320): Title->getArticleID(integer)
#7 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/Title.php(4395): Title->exists()
#8 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/linker/LinkRenderer.php(149): Title->isKnown()
#9 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/OutputPage.php(2738): MediaWiki\Linker\LinkRenderer->makeLink(Title, NULL, array, array)
#10 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/OutputPage.php(2774): OutputPage->addReturnTo(Title, array)
#11 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/OutputPage.php(2519): OutputPage->returnToMain()
#12 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/exception/ErrorPageError.php(68): OutputPage->showErrorPage(string, string, array)
#13 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/exception/BadRequestError.php(32): ErrorPageError->report()
#14 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/MediaWiki.php(529): BadRequestError->report()
#15 /var/www/wiki.ellak.gr/el.diadikasies.gr/index.php(43): MediaWiki->run()
#16 {main}

Exception caught inside exception handler: [a251dfaeaec1a3b422d2c468] /index.php?title=%25CE%2595%25CE%25B9%25CE%25B4%25CE%25B9%25CE%25BA%25CF%258C:%25CE%25A3%25CF%258D%25CE%25BD%25CE%25B4%25CE%25B5%25CF%2583%25CE%25B7%25CE%25A7%25CF%2581%25CE%25AE%25CF%2583%25CF%2584%25CE%25B7&returnto=%25CE%2591%25CE%25BB%25CE%25BB%25CE%25B1%25CE%25B3%25CE%25AE+%25CE%25B5%25CF%2580%25CF%2589%25CE%25BD%25CF%2585%25CE%25BC%25CE%25AF%25CE%25B1%25CF%2582+%25CE%25B2%25CE%25B9%25CE%25BF%25CF%2584%25CE%25B5%25CF%2587%25CE%25BD%25CE%25B9%25CE%25BA%25CE%25AE%25CF%2582+%25CE%25BC%25CE%25BF%25CE%25BD%25CE%25AC%25CE%25B4%25CE%25B1%25CF%2582&returntoquery=oldid%253D12655 Wikimedia\Rdbms\DBConnectionError from line 769 of /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/libs/rdbms/database/Database.php: Cannot access the database: Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111) (localhost:3306)
Backtrace:
#0 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/libs/rdbms/loadbalancer/LoadBalancer.php(995): Wikimedia\Rdbms\Database->reportConnectionError(string)
#1 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/libs/rdbms/loadbalancer/LoadBalancer.php(666): Wikimedia\Rdbms\LoadBalancer->reportConnectionError()
#2 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/GlobalFunctions.php(3062): Wikimedia\Rdbms\LoadBalancer->getConnection(integer, array, boolean)
#3 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/cache/LinkBatch.php(197): wfGetDB(integer)
#4 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/cache/LinkBatch.php(139): LinkBatch->doQuery()
#5 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/cache/LinkBatch.php(128): LinkBatch->executeInto(LinkCache)
#6 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/skins/Skin.php(247): LinkBatch->execute()
#7 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/skins/Skin.php(145): Skin->preloadExistence()
#8 /var/www/wiki.ellak.gr/pool.diadikasies.gr/skins/Vector/SkinVector.php(47): Skin->initPage(OutputPage)
#9 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/skins/SkinTemplate.php(248): SkinVector->initPage(OutputPage)
#10 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/OutputPage.php(2441): SkinTemplate->outputPage()
#11 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/exception/MWExceptionRenderer.php(186): OutputPage->output()
#12 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/exception/MWExceptionRenderer.php(55): MWExceptionRenderer::reportHTML(Wikimedia\Rdbms\DBQueryError)
#13 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/exception/MWExceptionHandler.php(75): MWExceptionRenderer::output(Wikimedia\Rdbms\DBQueryError, integer)
#14 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/exception/MWExceptionHandler.php(130): MWExceptionHandler::report(Wikimedia\Rdbms\DBQueryError)
#15 /var/www/wiki.ellak.gr/pool.diadikasies.gr/includes/MediaWiki.php(551): MWExceptionHandler::handleException(Wikimedia\Rdbms\DBQueryError)
#16 /var/www/wiki.ellak.gr/el.diadikasies.gr/index.php(43): MediaWiki->run()
#17 {main}