Всё сломалось!

Класс: DB

engine::run();
engine::getCart();
DB::execSQL("SELECT * FROM cart WHERE order_id="" AND sid="v5708m2iup5hk3akten49bsopg"");

SELECT * FROM cart WHERE order_id="" AND sid="v5708m2iup5hk3akten49bsopg"
MySQL server has gone away