Codeigniter很少会加载数据库连接

I am having a very annoying issue, I could not find a solution or cause. Very rarely, calling a CodeIgniter function it stucks for about 15 minutes. I was able to find, that CI database load is causing such issue. After 15 minutes get an error MySQL server has gone away.

My database config:

$db['local'] = array(
    'dsn' => '',
    'hostname' => 'localhost',
    'username' => '******',
    'password' => '********',
    'database' => '********',
    'dbdriver' => 'mysqli',
    'dbprefix' => '',
    'pconnect' => true,
    'db_debug' => (ENVIRONMENT !== 'production'),
    'cache_on' => false,
    'cachedir' => '',
    'char_set' => 'utf8',
    'dbcollat' => 'utf8_general_ci',
    'swap_pre' => '',
    'encrypt' => false,
    'compress' => false,
    'stricton' => false,
    'failover' => array(),
    'save_queries' => true,
);

It might be because of connection timeout time, try setting

$db['default']['options'] = array(PDO::ATTR_TIMEOUT => 5);

found here: Set database connection timeout in CodeIgniter 3