MediaWiki internal error.

Original exception: exception 'DBQueryError' with message 'A database error has occurred
Query: DELETE FROM `objectcache` WHERE exptime < '20140919235505'
Function: MediaWikiBagOStuff::_doquery
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, 'DELETE FROM `ob...', 'MediaWikiBagOSt...', false)
#1 /usr/share/mediawiki1.7/includes/BagOStuff.php(433): Database->query('DELETE FROM `ob...', 'MediaWikiBagOSt...')
#2 /usr/share/mediawiki1.7/includes/BagOStuff.php(319): MediaWikiBagOStuff->_doquery('DELETE FROM `ob...')
#3 /usr/share/mediawiki1.7/includes/BagOStuff.php(373): SqlBagOStuff->_query('DELETE FROM $0 ...')
#4 /usr/share/mediawiki1.7/includes/BagOStuff.php(362): SqlBagOStuff->expireall()
#5 /usr/share/mediawiki1.7/includes/BagOStuff.php(237): SqlBagOStuff->garbageCollect()
#6 /usr/share/mediawiki1.7/includes/ChangesFeed.php(63): SqlBagOStuff->get('wikidb::atom:ti...')
#7 /usr/share/mediawiki1.7/includes/ChangesFeed.php(38): ChangesFeed->loadFromCache('20140918053730', 'wikidb::atom:ti...', 'wikidb::atom:li...')
#8 /usr/share/mediawiki1.7/includes/specials/SpecialRecentchanges.php(121): ChangesFeed->execute(Object(AtomFeed), Array, 50, false, '20140918053730')
#9 /usr/share/mediawiki1.7/includes/SpecialPage.php(534): SpecialRecentChanges->execute(NULL)
#10 /usr/share/mediawiki1.7/includes/Wiki.php(224): SpecialPage::executePath(Object(Title))
#11 /usr/share/mediawiki1.7/includes/Wiki.php(55): MediaWiki->initializeSpecialCases(Object(Title), Object(OutputPage), Object(WebRequest))
#12 /var/lib/mediawiki1.7/index.php(93): MediaWiki->initialize(Object(Title), NULL, Object(OutputPage), Object(User), Object(WebRequest))
#13 {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}