RocketMQ集群消费时队列分配
何时需要消息队列
业务解耦
最终一致性
广播
错峰流控
RocketMQ的核心概念
详情见于文档
PushConsumer调用负载均衡的方法
public void doRebalance() {
if (this.rebalanceImpl != null && !this.pause) {
this.rebalanceImpl.doRebalance(this.isConsumeOrderly());
}
}
可以看出真正负载均衡的是rebalanceImpl这个成员变量的工作,在RebelanceImpl类中代码为
public void doRebalance(final boolean isOrder) {
Map subTable = this.getSubscriptionInner();
if (subTable != null) {
for (final Map.Entry entry : subTable.entrySet()) {
final String topic = entry.getKey();
try {
this.rebalanceByTopic(topic, isOrder);
} catch (Exception e) {
if (!topic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
log.warn("rebalanceByTopic Exception", e);
}
}
}
}
this.truncateMessageQueueNotMyTopic();
}
获取订阅关系，订阅关系是在consumer.start()中从consumer中复制过来的,订阅关系是以topic为key，tags组成的subscriptionData。
第二步遍历订阅关系，调用rebalanceByTopc(topic,isOrder)方法，根据topic和isOrder进行负载均衡
遍历结束，调用truncateMessageQueueNotMyTopic()方法，去除不属于当前consumer的topic对应的消息队列
分析rebalanceByTopic方法
private void rebalanceByTopic(final String topic, final boolean isOrder) {
switch (messageModel) {
case CLUSTERING: {
//SD:集群模式下,从订阅信息表中获取topic对应的所有消息队列
Set mqSet = this.topicSubscribeInfoTable.get(topic);
//SD:根据topic和consumerGroupName获取所有相关的consumerId
//SD:此处如果同一个consumerGroupName下面的订阅关系不一致的话，会导致消息消费失败
List cidAll = this.mQClientFactory.findConsumerIdList(topic, consumerGroup);
if (null == mqSet) {
if (!topic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
log.warn("doRebalance, {}, but the topic[{}] not exist.", consumerGroup, topic);
}
}
if (null == cidAll) {
log.warn("doRebalance, {} {}, get consumer id list failed", consumerGroup, topic);
}
if (mqSet != null && cidAll != null) {
List mqAll = new ArrayList();
mqAll.addAll(mqSet);
Collections.sort(mqAll);
Collections.sort(cidAll);
AllocateMessageQueueStrategy strategy = this.allocateMessageQueueStrategy;
List allocateResult = null;
//把所有的消息队列按照配置的分配策略进行分配，获取当前consumer获得的消息队列
try {
allocateResult = strategy.allocate(//
this.consumerGroup, //
this.mQClientFactory.getClientId(), //
mqAll, //
cidAll);
} catch (Throwable e) {
log.error("AllocateMessageQueueStrategy.allocate Exception. allocateMessageQueueStrategyName={}", strategy.getName(),
e);
return;
}
Set allocateResultSet = new HashSet();
if (allocateResult != null) {
allocateResultSet.addAll(allocateResult);
}
//根据负载均衡的结果更新处理队列，consumer根据消息队列拉取消息
//移除不属于当前consumer的队列或者距离上次拉取时间超过最大间隔的队列
boolean changed = this.updateProcessQueueTableInRebalance(topic, allocateResultSet, isOrder);
if (changed) {
log.info(
"rebalanced result changed. allocateMessageQueueStrategyName={}, group={}, topic={}, clientId={}, mqAllSize={}, cidAllSize={}, rebalanceResultSize={}, rebalanceResultSet={}",
strategy.getName(), consumerGroup, topic, this.mQClientFactory.getClientId(), mqSet.size(), cidAll.size(),
allocateResultSet.size(), allocateResultSet);
this.messageQueueChanged(topic, mqSet, allocateResultSet);
}
}
break;
}
default:
break;
}
}
默认情况下，使用平均分配消息队列的策略;
分析truncateMessageQueueNotMyTopic方法
private void truncateMessageQueueNotMyTopic() {
//获取从consumer处copy的订阅关系
Map subTable = this.getSubscriptionInner();
//遍历自己的执行队列的消息队列集合
// 如果目标消息队列的topic不存在当前的订阅关系中，移除这个消息队列
for (MessageQueue mq : this.processQueueTable.keySet()) {
if (!subTable.containsKey(mq.getTopic())) {
ProcessQueue pq = this.processQueueTable.remove(mq);
if (pq != null) {
pq.setDropped(true);
log.info("doRebalance, {}, truncateMessageQueueNotMyTopic remove unnecessary mq, {}", consumerGroup, mq);
}
}
}
}
什么时候负载均衡
在consumer启动的过程中，rebalanceImpl会从consumer处复制订阅关系
public void start() throws MQClientException {
switch (this.serviceState) {
case CREATE_JUST:
log.info("the consumer [{}] start beginning. messageModel={}, isUnitMode={}", this.defaultMQPushConsumer.getConsumerGroup(),
this.defaultMQPushConsumer.getMessageModel(), this.defaultMQPushConsumer.isUnitMode());
this.serviceState = ServiceState.START_FAILED;
this.checkConfig();
//复制订阅关系
this.copySubscription();
if (this.defaultMQPushConsumer.getMessageModel() == MessageModel.CLUSTERING) {
this.defaultMQPushConsumer.changeInstanceNameToPID();
}
this.mQClientFactory = MQClientManager.getInstance().getAndCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);
this.rebalanceImpl.setConsumerGroup(this.defaultMQPushConsumer.getConsumerGroup());
this.rebalanceImpl.setMessageModel(this.defaultMQPushConsumer.getMessageModel());
this.rebalanceImpl.setAllocateMessageQueueStrategy(this.defaultMQPushConsumer.getAllocateMessageQueueStrategy());
this.rebalanceImpl.setmQClientFactory(this.mQClientFactory);
this.pullAPIWrapper = new PullAPIWrapper(//
mQClientFactory, //
this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());
this.pullAPIWrapper.registerFilterMessageHook(filterMessageHookList);
if (this.defaultMQPushConsumer.getOffsetStore() != null) {
this.offsetStore = this.defaultMQPushConsumer.getOffsetStore();
} else {
switch (this.defaultMQPushConsumer.getMessageModel()) {
case BROADCASTING:
this.offsetStore = new LocalFileOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
break;
case CLUSTERING:
this.offsetStore = new RemoteBrokerOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
break;
default:
break;
}
}
this.offsetStore.load();
if (this.getMessageListenerInner() instanceof MessageListenerOrderly) {
this.consumeOrderly = true;
this.consumeMessageService =
new ConsumeMessageOrderlyService(this, (MessageListenerOrderly) this.getMessageListenerInner());
} else if (this.getMessageListenerInner() instanceof MessageListenerConcurrently) {
this.consumeOrderly = false;
this.consumeMessageService =
new ConsumeMessageConcurrentlyService(this, (MessageListenerConcurrently) this.getMessageListenerInner());
}
//启动消费消息的服务
this.consumeMessageService.start();
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);
}
//启动工厂方法
mQClientFactory.start();
log.info("the consumer [{}] start OK.", this.defaultMQPushConsumer.getConsumerGroup());
this.serviceState = ServiceState.RUNNING;
break;
case RUNNING:
case START_FAILED:
case SHUTDOWN_ALREADY:
throw new MQClientException("The PushConsumer service state not OK, maybe started once, "//
+ this.serviceState//
+ FAQUrl.suggestTodo(FAQUrl.CLIENT_SERVICE_NOT_OK),
null);
default:
break;
}
//当订阅关系发生变化省，更新订阅关系
this.updateTopicSubscribeInfoWhenSubscriptionChanged();
this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
//立即负载均衡
this.mQClientFactory.rebalanceImmediately();
}
工厂方法启动逻辑
public void start() throws MQClientException {
synchronized (this) {
switch (this.serviceState) {
case CREATE_JUST:
this.serviceState = ServiceState.START_FAILED;
// If not specified,looking address from name server
if (null == this.clientConfig.getNamesrvAddr()) {
this.clientConfig.setNamesrvAddr(this.mQClientAPIImpl.fetchNameServerAddr());
}
// Start request-response channel
this.mQClientAPIImpl.start();
// Start various schedule tasks
this.startScheduledTask();
// Start pull service
this.pullMessageService.start();
// Start rebalance service
this.rebalanceService.start();
// Start push service
this.defaultMQProducer.getDefaultMQProducerImpl().start(false);
log.info("the client factory [{}] start OK", this.clientId);
this.serviceState = ServiceState.RUNNING;
break;
case RUNNING:
break;
case SHUTDOWN_ALREADY:
break;
case START_FAILED:
throw new MQClientException("The Factory object[" + this.getClientId() + "] has been created before, and failed.", null);
default:
break;
}
}
}
rebalanceService是一个线程任务类,在线程任务中定时factory执行调用负载均衡
public void run() {
log.info(this.getServiceName() + " service started");
while (!this.isStoped()) {
this.waitForRunning(WaitInterval);
this.mqClientFactory.doRebalance();
}
log.info(this.getServiceName() + " service end");
}
factory执行负载均衡，其实就是遍历factory中的所有consumer，调用doRebalance()方法
public void doRebalance() {
for (Map.Entry entry : this.consumerTable.entrySet()) {
MQConsumerInner impl = entry.getValue();
if (impl != null) {
try {
impl.doRebalance();
} catch (Exception e) {
log.error("doRebalance exception", e);
}
}
}
}
AllocateMessageQueueStrategy 队列分配策略
默认情况下PushConsumer的AllocateMessageQueueStrategy
public DefaultMQPushConsumer() {
this(MixAll.DEFAULT_CONSUMER_GROUP, null, new AllocateMessageQueueAveragely());
}