presto-main/src/main/java/io/prestosql/SystemSessionProperties.java/SystemSessionProperties/getJoinMaxBroadcastTableSize
class SystemSessionProperties:    public static Optional<DataSize> getJoinMaxBroadcastTableSize(Session session)
    {
        return Optional.ofNullable(session.getSystemProperty(JOIN_MAX_BROADCAST_TABLE_SIZE, DataSize.class));
    }