Uncaught exception: 'SQLSTATE[HY000] [2002] Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)'
More information

In /home/sites/site4/web/libs/Zend/Db/Adapter/Pdo/Abstract.php on line 131
Backtrace:

#0 /home/sites/site4/web/libs/Zend/Db/Adapter/Abstract.php(228): Zend_Db_Adapter_Pdo_Abstract->_connect()
#1 /home/sites/site4/web/modules/Piwik.php(862): Zend_Db_Adapter_Abstract->getConnection()
#2 /home/sites/site4/web/modules/FrontController.php(310): Piwik::createDatabaseObject()
#3 /home/sites/site4/web/index.php(54): Piwik_FrontController->init()
#4 {main}

You can get help from http://piwik.org (give us the full error message + your PHP and Mysql version)

And this exception raised another exception "No entry is registered for key 'logger_exception'"