MediaWiki internal error.

Original exception: exception 'DBQueryError' with message 'A database error has occurred
Query: SELECT `recentchanges`.* FROM `recentchanges` INNER JOIN `categorylinks` ON ((rc_cur_id = cl_from)) WHERE (rc_timestamp >= '20140915000000') AND rc_bot = '0' AND cl_to = 'Mongolian_Personas' ORDER BY rc_timestamp DESC LIMIT 50
Function: SpecialRecentchangeslinked::doMainQuery
Error: 2002 Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111) (localhost)
' in /usr/share/mediawiki1.7/includes/db/Database.php:606
Stack trace:
#0 /usr/share/mediawiki1.7/includes/db/Database.php(561): Database->reportQueryError('Can't connect t...', 2002, 'SELECT `recent...', 'SpecialRecentch...', false)
#1 /usr/share/mediawiki1.7/includes/specials/SpecialRecentchangeslinked.php(146): Database->query('SELECT `recent...', 'SpecialRecentch...')
#2 /usr/share/mediawiki1.7/includes/specials/SpecialRecentchanges.php(102): SpecialRecentchangeslinked->doMainQuery(Array, Object(FormOptions))
#3 /usr/share/mediawiki1.7/includes/SpecialPage.php(534): SpecialRecentChanges->execute('Category:Mongol...')
#4 /usr/share/mediawiki1.7/includes/Wiki.php(224): SpecialPage::executePath(Object(Title))
#5 /usr/share/mediawiki1.7/includes/Wiki.php(55): MediaWiki->initializeSpecialCases(Object(Title), Object(OutputPage), Object(WebRequest))
#6 /var/lib/mediawiki1.7/index.php(93): MediaWiki->initialize(Object(Title), NULL, Object(OutputPage), Object(User), Object(WebRequest))
#7 {main}

Exception caught inside exception handler: exception 'DBUnexpectedError' with message 'Error in fetchObject(): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (111) (localhost)' in /usr/share/mediawiki1.7/includes/db/Database.php:735
Stack trace:
#0 /usr/share/mediawiki1.7/includes/db/Database.php(2620): Database->fetchObject(false)
#1 /usr/share/mediawiki1.7/includes/LinkBatch.php(98): ResultWrapper->fetchObject()
#2 /usr/share/mediawiki1.7/includes/LinkBatch.php(78): LinkBatch->addResultToCache(Object(LinkCache), Object(ResultWrapper))
#3 /usr/share/mediawiki1.7/includes/LinkBatch.php(68): LinkBatch->executeInto(Object(LinkCache))
#4 /usr/share/mediawiki1.7/includes/Skin.php(208): LinkBatch->execute()
#5 /usr/share/mediawiki1.7/includes/Skin.php(184): Skin->preloadExistence()
#6 /usr/share/mediawiki1.7/includes/SkinTemplate.php(106): Skin->initPage(Object(OutputPage))
#7 /usr/share/mediawiki1.7/skins/MonoBook.php(24): SkinTemplate->initPage(Object(OutputPage))
#8 /usr/share/mediawiki1.7/includes/SkinTemplate.php(151): SkinMonoBook->initPage(Object(OutputPage))
#9 /usr/share/mediawiki1.7/includes/OutputPage.php(821): SkinTemplate->outputPage(Object(OutputPage))
#10 /usr/share/mediawiki1.7/includes/Exception.php(150): OutputPage->output()
#11 /usr/share/mediawiki1.7/includes/Exception.php(174): MWException->reportHTML()
#12 /usr/share/mediawiki1.7/includes/Exception.php(260): MWException->report()
#13 /usr/share/mediawiki1.7/includes/Exception.php(294): wfReportException(Object(DBQueryError))
#14 [internal function]: wfExceptionHandler(Object(DBQueryError))
#15 {main}