聊聊rocketmq的订阅关系

序

本文主要研究一下rocketmq的订阅关系

报错

org.apache.rocketmq.client.exception.MQClientException: The consumer group[demo-group] has been created before, specify another name please.
See http://rocketmq.apache.org/docs/faq/ for further details.

    at org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl.start(DefaultMQPushConsumerImpl.java:629)
    at org.apache.rocketmq.client.consumer.DefaultMQPushConsumer.start(DefaultMQPushConsumer.java:693)

启动了两个consumer，分别消费topic1和topic2，但是都使用了同一个group，结果启动报错

DefaultMQPushConsumerImpl#start

org/apache/rocketmq/client/impl/consumer/DefaultMQPushConsumerImpl.java

                boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
                if (!registerOK) {
                    this.serviceState = ServiceState.CREATE_JUST;
                    this.consumeMessageService.shutdown();
                    throw new MQClientException("The consumer group[" + this.defaultMQPushConsumer.getConsumerGroup()
                        + "] has been created before, specify another name please." + FAQUrl.suggestTodo(FAQUrl.GROUP_NAME_DUPLICATE_URL),
                        null);
                }

DefaultMQPushConsumerImpl的start方法会使用mQClientFactory.registerConsumer去注册consumer，如果返回false则抛出MQClientException异常

registerConsumer

org/apache/rocketmq/client/impl/factory/MQClientInstance.java

public boolean registerConsumer(final String group, final MQConsumerInner consumer) {
        if (null == group || null == consumer) {
            return false;
        }

        MQConsumerInner prev = this.consumerTable.putIfAbsent(group, consumer);
        if (prev != null) {
            log.warn("the consumer group[" + group + "] exist already.");
            return false;
        }

        return true;
    }

MQClientInstance的registerConsumer使用consumerTable维护了group与consumer的关系，这里要求一个consumer group只能与一个consumer关联，如果不同consumer用了同一个group名称则会返回false

订阅一致性问题

@Test
    public void testConsume() throws MQClientException, InterruptedException {
        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("string_consumer_test");
        consumer.setNamesrvAddr("192.168.64.3:9876");
//        consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);
        consumer.subscribe("string-topic-new", "*");
        consumer.registerMessageListener((MessageListenerConcurrently) (msg, context) -> {
            System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msg);
            for (MessageExt ext : msg) {
                System.out.printf("consumer1: %s \n",new String(ext.getBody()));
            }
            return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
        });
        consumer.start();

        DefaultMQPushConsumer consumer2 = new DefaultMQPushConsumer("string_consumer_test");
        consumer2.setNamesrvAddr("192.168.64.3:9876");
//        consumer2.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);
        consumer2.subscribe("string-topic2-new", "*");
        consumer2.registerMessageListener((MessageListenerConcurrently) (msg, context) -> {
            System.out.printf("consumer2 %s Receive New Messages: %s %n", Thread.currentThread().getName(), msg);
            for (MessageExt ext : msg) {
                System.out.printf("consumer2: %s \n",new String(ext.getBody()));
            }
            return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
        });
        consumer2.start();

        System.out.printf("Consumer Started.%n");
        TimeUnit.HOURS.sleep(1);

    }

像如上代码，两个consumer使用了同一个group，但是他们订阅了不同的topic，这种最后会造成consumer1及consumer2不能如预期那样正常消费消息

DefaultMQPushConsumer.start()

org/apache/rocketmq/client/consumer/DefaultMQPushConsumer.java

public void start() throws MQClientException {
        setConsumerGroup(NamespaceUtil.wrapNamespace(this.getNamespace(), this.consumerGroup));
        this.defaultMQPushConsumerImpl.start();
        if (null != traceDispatcher) {
            try {
                traceDispatcher.start(this.getNamesrvAddr(), this.getAccessChannel());
            } catch (MQClientException e) {
                log.warn("trace dispatcher start failed ", e);
            }
        }
    }

DefaultMQPushConsumer的start方法执行的是defaultMQPushConsumerImpl.start()

DefaultMQPushConsumerImpl.start()

org/apache/rocketmq/client/impl/consumer/DefaultMQPushConsumerImpl.java

boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
//......
this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();

DefaultMQPushConsumerImpl.start()方法会执行mQClientFactory.registerConsumer，最后执行mQClientFactory.sendHeartbeatToAllBrokerWithLock()

MQClientInstance.registerConsumer

org/apache/rocketmq/client/impl/factory/MQClientInstance.java

    /**
     * The container of the consumer in the current client. The key is the name of consumerGroup.
     */
    private final ConcurrentMap<String, MQConsumerInner> consumerTable = new ConcurrentHashMap<>();

     public synchronized boolean registerConsumer(final String group, final MQConsumerInner consumer) {
        if (null == group || null == consumer) {
            return false;
        }

        MQConsumerInner prev = this.consumerTable.putIfAbsent(group, consumer);
        if (prev != null) {
            log.warn("the consumer group[" + group + "] exist already.");
            return false;
        }

        return true;
    }

MQClientInstance.registerConsumer方法以group为维度去注册consumer

MQClientInstance.sendHeartbeatToAllBrokerWithLock()

org/apache/rocketmq/client/impl/factory/MQClientInstance.java

    public void sendHeartbeatToAllBrokerWithLock() {
        if (this.lockHeartbeat.tryLock()) {
            try {
                this.sendHeartbeatToAllBroker();
                this.uploadFilterClassSource();
            } catch (final Exception e) {
                log.error("sendHeartbeatToAllBroker exception", e);
            } finally {
                this.lockHeartbeat.unlock();
            }
        } else {
            log.warn("lock heartBeat, but failed. [{}]", this.clientId);
        }
    }

    private HeartbeatData prepareHeartbeatData() {
        HeartbeatData heartbeatData = new HeartbeatData();

        // clientID
        heartbeatData.setClientID(this.clientId);

        // Consumer
        for (Map.Entry<String, MQConsumerInner> entry : this.consumerTable.entrySet()) {
            MQConsumerInner impl = entry.getValue();
            if (impl != null) {
                ConsumerData consumerData = new ConsumerData();
                consumerData.setGroupName(impl.groupName());
                consumerData.setConsumeType(impl.consumeType());
                consumerData.setMessageModel(impl.messageModel());
                consumerData.setConsumeFromWhere(impl.consumeFromWhere());
                consumerData.getSubscriptionDataSet().addAll(impl.subscriptions());
                consumerData.setUnitMode(impl.isUnitMode());

                heartbeatData.getConsumerDataSet().add(consumerData);
            }
        }

        // Producer
        for (Map.Entry<String/* group */, MQProducerInner> entry : this.producerTable.entrySet()) {
            MQProducerInner impl = entry.getValue();
            if (impl != null) {
                ProducerData producerData = new ProducerData();
                producerData.setGroupName(entry.getKey());

                heartbeatData.getProducerDataSet().add(producerData);
            }
        }

        return heartbeatData;
    }    

每次send heartbeat，broker都会处理这些信息

ClientManageProcessor.heartBeat

org/apache/rocketmq/broker/processor/ClientManageProcessor.java

    public RemotingCommand heartBeat(ChannelHandlerContext ctx, RemotingCommand request) {
        RemotingCommand response = RemotingCommand.createResponseCommand(null);
        HeartbeatData heartbeatData = HeartbeatData.decode(request.getBody(), HeartbeatData.class);
        ClientChannelInfo clientChannelInfo = new ClientChannelInfo(
            ctx.channel(),
            heartbeatData.getClientID(),
            request.getLanguage(),
            request.getVersion()
        );

        for (ConsumerData data : heartbeatData.getConsumerDataSet()) {
            SubscriptionGroupConfig subscriptionGroupConfig =
                this.brokerController.getSubscriptionGroupManager().findSubscriptionGroupConfig(
                    data.getGroupName());
            boolean isNotifyConsumerIdsChangedEnable = true;
            if (null != subscriptionGroupConfig) {
                isNotifyConsumerIdsChangedEnable = subscriptionGroupConfig.isNotifyConsumerIdsChangedEnable();
                int topicSysFlag = 0;
                if (data.isUnitMode()) {
                    topicSysFlag = TopicSysFlag.buildSysFlag(false, true);
                }
                String newTopic = MixAll.getRetryTopic(data.getGroupName());
                this.brokerController.getTopicConfigManager().createTopicInSendMessageBackMethod(
                    newTopic,
                    subscriptionGroupConfig.getRetryQueueNums(),
                    PermName.PERM_WRITE | PermName.PERM_READ, topicSysFlag);
            }

            boolean changed = this.brokerController.getConsumerManager().registerConsumer(
                data.getGroupName(),
                clientChannelInfo,
                data.getConsumeType(),
                data.getMessageModel(),
                data.getConsumeFromWhere(),
                data.getSubscriptionDataSet(),
                isNotifyConsumerIdsChangedEnable
            );

            if (changed) {
                log.info("registerConsumer info changed {} {}",
                    data.toString(),
                    RemotingHelper.parseChannelRemoteAddr(ctx.channel())
                );
            }
        }

        for (ProducerData data : heartbeatData.getProducerDataSet()) {
            this.brokerController.getProducerManager().registerProducer(data.getGroupName(),
                clientChannelInfo);
        }
        response.setCode(ResponseCode.SUCCESS);
        response.setRemark(null);
        return response;
    }

这里brokerController是根据groupName类注册consumer的，如果有changed，则会打印日志

2023-05-08 20:17:59 INFO HeartbeatThread_1 - registerConsumer info changed ConsumerData [groupName=string_consumer_test, consumeType=CONSUME_PASSIVELY, messageModel=CLUSTERING, consumeFromWhere=CONSUME_FROM_LAST_OFFSET, unitMode=false, subscriptionDataSet=[SubscriptionData [classFilterMode=false, topic=string-topic-new, subString=*, tagsSet=[], codeSet=[], subVersion=1683548105549, expressionType=TAG], SubscriptionData [classFilterMode=false, topic=%RETRY%string_consumer_test, subString=*, tagsSet=[], codeSet=[], subVersion=1683548138803, expressionType=TAG]]] 192.168.64.1:51651
2023-05-08 20:19:01 INFO HeartbeatThread_2 - registerConsumer info changed ConsumerData [groupName=string_consumer_test, consumeType=CONSUME_PASSIVELY, messageModel=CLUSTERING, consumeFromWhere=CONSUME_FROM_LAST_OFFSET, unitMode=false, subscriptionDataSet=[SubscriptionData [classFilterMode=false, topic=string-topic2-new, subString=*, tagsSet=[], codeSet=[], subVersion=1683548243594, expressionType=TAG], SubscriptionData [classFilterMode=false, topic=%RETRY%string_consumer_test, subString=*, tagsSet=[], codeSet=[], subVersion=1683548247027, expressionType=TAG]]] 192.168.64.1:51675

ConsumerManager.registerConsumer

org/apache/rocketmq/broker/client/ConsumerManager.java

private final ConcurrentMap<String/* Group */, ConsumerGroupInfo> consumerTable =
        new ConcurrentHashMap<String, ConsumerGroupInfo>(1024);

public boolean registerConsumer(final String group, final ClientChannelInfo clientChannelInfo,
        ConsumeType consumeType, MessageModel messageModel, ConsumeFromWhere consumeFromWhere,
        final Set<SubscriptionData> subList, boolean isNotifyConsumerIdsChangedEnable) {

        ConsumerGroupInfo consumerGroupInfo = this.consumerTable.get(group);
        if (null == consumerGroupInfo) {
            ConsumerGroupInfo tmp = new ConsumerGroupInfo(group, consumeType, messageModel, consumeFromWhere);
            ConsumerGroupInfo prev = this.consumerTable.putIfAbsent(group, tmp);
            consumerGroupInfo = prev != null ? prev : tmp;
        }

        boolean r1 =
            consumerGroupInfo.updateChannel(clientChannelInfo, consumeType, messageModel,
                consumeFromWhere);
        boolean r2 = consumerGroupInfo.updateSubscription(subList);

        if (r1 || r2) {
            if (isNotifyConsumerIdsChangedEnable) {
                this.consumerIdsChangeListener.handle(ConsumerGroupEvent.CHANGE, group, consumerGroupInfo.getAllChannel());
            }
        }

        this.consumerIdsChangeListener.handle(ConsumerGroupEvent.REGISTER, group, subList);

        return r1 || r2;
    }

每次heartbeat都会执行registerConsumer，而key是consumerGroup，这样子会造成broker端的订阅关系时而是consumer1的，时而是consumer2的，最终造成消息延时或者消息消费不到的问题

小结

rocketmq的订阅关系要求使用同一个consumer group的不同consumer它们对topic及tag的订阅关系要一致，不然会造成消息未能如期消费等异常，其本质是broker端维护了key为group的ConsumerGroupInfo，而每次consumer的heartbeat则会在broker端变更同一个group的ConsumerData信息，造成订阅关系不断被变更。

doc

• 消费者分组（ConsumerGroup）
• 订阅关系（Subscription）
• 我擦，RocketMQ的tag还有这个“坑”！
• RocketMQ同一个消费者内消费者订阅不同Topic问题分析