MySQL数据库PHP连接池的配置与应用有何关键优势？

 <?php // 创建数据库连接池配置 $host = '127.0.0.1'; // 数据库服务器地址 $port = '3306'; // 数据库服务器端口 $user = 'root'; // 数据库用户名 $pass = 'password'; // 数据库密码 $database = 'test_db'; // 数据库名 $charset = 'utf8mb4'; // 字符集 $poolSize = 5; // 连接池大小 // 数据库连接池类 class MySQLiConnectionPool {     private $host;     private $port;     private $user;     private $pass;     private $database;     private $charset;     private $pool;     private $availableConnections;     public function __construct($host, $port, $user, $pass, $database, $charset, $poolSize) {         $this>host = $host;         $this>port = $port;         $this>user = $user;         $this>pass = $pass;         $this>database = $database;         $this>charset = $charset;         $this>poolSize = $poolSize;         $this>pool = [];         $this>availableConnections = new SplQueue();         for ($i = 0; $i < $poolSize; $i++) {             $this>availableConnections>enqueue($this>createConnection());         }     }     private function createConnection() {         return new mysqli($this>host, $this>user, $this>pass, $this>database, $this>port, null, $this>charset);     }     public function getConnection() {         if ($this>availableConnections>isEmpty()) {             $connection = $this>createConnection();             $this>pool[] = $connection;         } else {             $connection = $this>availableConnections>dequeue();         }         if ($connection>connect_error) {             $connection>close();             $connection = $this>createConnection();             $this>pool[] = $connection;         }         return $connection;     }     public function releaseConnection($connection) {         if ($connection instanceof mysqli) {             $this>availableConnections>enqueue($connection);         }     }     public function closeAllConnections() {         foreach ($this>pool as $connection) {             $connection>close();         }     } } // 使用连接池 $connectionPool = new MySQLiConnectionPool($host, $port, $user, $pass, $database, $charset, $poolSize); // 获取数据库连接 $connection = $connectionPool>getConnection(); // 执行数据库操作... // 释放数据库连接 $connectionPool>releaseConnection($connection); // 关闭所有连接 $connectionPool>closeAllConnections(); ?>

代码展示了如何创建一个简单的MySQLi连接池，连接池使用SplQueue来管理可用的连接，并在需要时创建新的连接，当连接不再需要时，它会被释放回连接池，可以通过调用closeAllConnections方法来关闭所有连接。