Azure Database for MySQL - Flexible Server is very slow

Question

Hi. I have a problem with performance of my mysql flexible server. When I use the same mysql version with default configuration but as a separate VM I see much better performance.

I am pretty sure it's not database/application configuration issue but network issue.

I created a script to test the performance:

function after($msg)
{
    global $tsts;
    if (isset($tsts)) {
        $time = floor((microtime(true) - $tsts) * 1000);
    } else {
        $time = 0;
    }
    print "{$msg}: {$time} ms\n";
    $tsts = microtime(true);
}

$options = [
    PDO::MYSQL_ATTR_INIT_COMMAND => 'SET NAMES utf8',
    PDO::MYSQL_ATTR_SSL_CA => '/home/azureuser/certs/ssl.pem',
    PDO::ATTR_PERSISTENT => true,
    PDO::ERRMODE_EXCEPTION => true,
];
$pdo = new PDO(
    'mysql:host=' . $host . ';dbname=db',
    $username,
    $password,
    $options
);
after("init");
$res = $pdo->query('SHOW TABLES;');
after("show tables");
for ($i = 1; $i <= 10; $i++) {
    $res = $pdo->query('SELECT * FROM test LIMIT 50');
}
after('selects');

and for the flexible server it prints:

$ php mysql_test.php 
init: 0 ms
show tables: 6 ms
selects: 18 ms
$ php mysql_test.php 
init: 0 ms
show tables: 6 ms
selects: 18 ms
$ php mysql_test.php 
init: 0 ms
show tables: 23 ms
selects: 18 ms

but for mysql installed on app vm directly it prints:

$ php mysql_test.php 
init: 0 ms
show tables: 5 ms
selects: 3 ms
$ php mysql_test.php 
init: 0 ms
show tables: 4 ms
selects: 2 ms
$ php mysql_test.php 
init: 0 ms
show tables: 4 ms
selects: 3 ms

Maybe these values seem to be low but when I look at my real app it takes 1m30s vs 25s to execute db migrations.

Where is the problem and how can I fix it?