presto-main/src/main/java/io/prestosql/SystemSessionProperties.java/SystemSessionProperties/getJoinReorderingStrategy
class SystemSessionProperties:    public static JoinReorderingStrategy getJoinReorderingStrategy(Session session)
    {
        Boolean reorderJoins = session.getSystemProperty(REORDER_JOINS, Boolean.class);
        if (reorderJoins != null) {
            if (!reorderJoins) {
                return NONE;
            }
            return ELIMINATE_CROSS_JOINS;
        }
        return session.getSystemProperty(JOIN_REORDERING_STRATEGY, JoinReorderingStrategy.class);
    }