PDO异常：SQLSTATE[HY000] [2006] MySQL服务器已断开连接，位于/var/www/app/src/Database/Connection.php:42

解决方案

1. Increase MySQL's wait_timeout and interactive_timeout in my.cnf, e.g., set wait_timeout=28800; interactive_timeout=28800. Then restart MySQL.

2. Increase max_allowed_packet in my.cnf to handle large queries, e.g., set max_allowed_packet=64M. Restart MySQL.

3. Implement connection retry logic in PHP: catch the exception and reconnect using a new PDO instance. Example:
   try {
       $stmt = $pdo->query('SELECT 1');
   } catch (\PDOException $e) {
       if ($e->getCode() == 2006) {
           $pdo = new PDO($dsn, $user, $pass);
           $stmt = $pdo->query('SELECT 1');
       }
   }