IOS使用mosquitto如何设置持久化？

如下代码是初始化 mosquitto，网上查了只要设置cleansession为false就表示是持久化订阅了，但是测试下来并没有实现持久化的功能。求大神帮忙哈，小弟万分感谢！！！


- (MosquittoClient*) initWithClientId: (NSString*) clientId {
    if ((self = [super init])) {
        const char* cstrClientId = [clientId cStringUsingEncoding:NSUTF8StringEncoding];
        [self setHost: nil];
        [self setPort: 1883];
        [self setKeepAlive: 60];
        [self setCleanSession: YES]; //NOTE: this isdisable clean to keep the broker remember this client

        mosq = mosquitto_new(cstrClientId, cleanSession, self);
        mosquitto_connect_callback_set(mosq, on_connect);
        mosquitto_disconnect_callback_set(mosq, on_disconnect);
        mosquitto_publish_callback_set(mosq, on_publish);
        mosquitto_message_callback_set(mosq, on_message);
        mosquitto_subscribe_callback_set(mosq, on_subscribe);
        mosquitto_unsubscribe_callback_set(mosq, on_unsubscribe);
        timer = nil;
    }
    return self;
}