为此,MysqL协议支持特殊命令COM_PING,并且C API有一个调用 mysql_ping()来发送它.这将测试连接是否处于活动状态.

如果使用MysqL_OPT_RECONNECT创建连接,则自动连接(https://dev.mysql.com/doc/refman/5.6/en/auto-reconnect.html).

遗憾的是,如果您使用当前版本的PDO,则不支持这些功能.您只能提交SQL查询字符串,而不能提交特殊命令. PDO现在使用MysqLnd驱动程序,它有其优点,但不支持重新连接选项.所以问题无论如何都是没有意义的.

我不知道比尝试发出像SELECT 1这样的“虚拟”查询更好的解决方案,如果你得到错误代码2006(服务器已经消失),那么重新连接.

您可以创建一个单独的类来保存数据库连接,并在每次应用程序代码调用getConnection()时测试实时连接.这是我测试的一个例子：

class DB
{
    PRotected static $pdo = null;

    public static function getConnection() {
        // inITialize $pdo on First call
        if (self::$pdo == null) {
            self::init();
        }

        // Now we should have a $pdo,whether it was initialized on this call or a prevIoUs one
        // but it Could have experienced a disconnection
        try {
            echo "testing connection...\n";
            $old_errlevel = error_reporting(0);
            self::$pdo->query("SELECT 1");
        } catch (PDOException $e) {
            echo "Connection Failed,reinitializing...\n";
            self::init();
        }
        error_reporting($old_errlevel);

        return self::$pdo;
    }

    protected static function init() {
        try {
            echo "opening new connection...\n";
            self::$pdo = new PDO('MysqL:host=huey;dbname=test','root','root');
            self::$pdo->setattribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
        } catch (PDOException $e) {
            die($e->getMessage());
        }
    }
}

像这样用它：

echo "Query for 2:\n";
$pdo = DB::getConnection();
echo $pdo->query("SELECT 2")->fetchColumn() . "\n";

echo "\nSleeping 10 seconds...\n";
sleep(10); /* meanwhile I use another window to KILL the connection */
echo "\n";

echo "Query for 3:\n";
$pdo = DB::getConnection();
echo $pdo->query("SELECT 3")->fetchColumn() . "\n";

输出：

Query for 2:
opening new connection...
Testing connection...
2

Sleeping 10 seconds...

Query for 3:
Testing connection...
Connection Failed,reinitializing...
opening new connection...
3

您可以看到它检测到连接失败,并重新初始化.