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。