Uncaught exception thrown in session handler.

PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away: SELECT 1 AS expression FROM {sessions} sessions WHERE ( (sid = :db_condition_placeholder_0) AND (ssid = :db_condition_placeholder_1) ); Array ( [:db_condition_placeholder_0] => LiwEG3T-adxhAq8SxuVKvaagbDY5vqLhH3CECbHX1Fo [:db_condition_placeholder_1] => LiwEG3T-adxhAq8SxuVKvaagbDY5vqLhH3CECbHX1Fo ) in _drupal_session_write() (line 209 of /var/www/promcom7/data/www/prom-com.ru/includes/session.inc).