怎么解决啊

错误页面：

Warning: PDO::__construct(): MySQL server has gone away in E:\xampp\htdocs\ceshi\mvc\model\Db3.php on line 74

Warning: PDO::__construct(): Error while reading greeting packet. PID=11512 in E:\xampp\htdocs\ceshi\mvc\model\Db3.php on line 74

Warning: Uncaught exception 'PDOException' with message 'SQLSTATE[HY000] [2006] MySQL server has gone away' in E:\xampp\htdocs\ceshi\mvc\model\Db3.php:74 Stack trace: #0 E:\xampp\htdocs\ceshi\mvc\model\Db3.php(74): PDO->__construct('mysql:host=127....', 'root', '') #1 E:\xampp\htdocs\ceshi\mvc\model\Db3.php(39): Db->connect() #2 E:\xampp\htdocs\ceshi\mvc\model\Db3.php(57): Db->__construct(Array) #3 E:\xampp\htdocs\ceshi\mvc\demo.php(11): Db::getInstance() #4 {main} thrown in E:\xampp\htdocs\ceshi\mvc\model\Db3.php on line 74

Fatal error: Maximum execution time of 30 seconds exceeded in E:\xampp\htdocs\ceshi\mvc\model\Db3.php on line 74