presto-main/src/main/java/io/prestosql/SystemSessionProperties.java/SystemSessionProperties/getMaxDriversPerTask
class SystemSessionProperties:    public static OptionalInt getMaxDriversPerTask(Session session)
    {
        Integer value = session.getSystemProperty(MAX_DRIVERS_PER_TASK, Integer.class);
        if (value == null) {
            return OptionalInt.empty();
        }
        return OptionalInt.of(value);
    }