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本文主要研究一下rocketmq的订阅关系
报错
代码语言：txt复制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
代码语言：txt复制 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
代码语言：txt复制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
代码语言：txt复制@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
代码语言：txt复制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
代码语言：txt复制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
代码语言：txt复制 /**
* 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
代码语言：txt复制 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
代码语言：txt复制 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;
}代码语言：txt复制这里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]]] 192.168.64.1:51675ConsumerManager.registerConsumer
org/apache/rocketmq/broker/client/ConsumerManager.java
代码语言：txt复制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
