Consumer

consumer pull message

接收消息

consumer启动的时候会启动两个service：

RebalanceService：主要实现consumer的负载均衡，但是并不会直接发送获取消息的请求，而是构造request之后放到PullMessageService中，等待PullMessageService的线程取出执行

PullMessageService：主要负责从broker获取message，包含一个需要获取消息的请求队列（是阻塞的），并不断依次从队列中取出请求向broker send Request

执行时序图太大，截屏截不全，所以放在git上，在

从Broker pullMessage

在PullMessageService中通过netty发送pull消息的请求之后，Broker的remoteServer会收到request，然后在PullMessageProcessor中的processRequest处理，先会解析requestHeader，request中带了读取MessageStore的参数：

consumerGroup

topic

queueId

queueOffset

MaxMsgNums

subscriptionData（ConsumerManager中获取）

processRequest处理流程

判断Broker当前是否允许接收消息

找到subscriptionGroupConfig，subscriptionGroupTable，如果不存在当前的group则新增一个

是否subscriptionGroupConfig.consumeEnable

获取从TopicConfigManager.topicConfigTable获取topicConfig

topicConfig是否有读权限

校验queueId是否在范围内

ConsumerManager.getConsumerGroupInfo获取ConsumerGroupInfo

consumerGroupInfo.findSubscriptionData查找subscriptionData

MessageStore.getMessage读取消息，从文件中读取消息，属于pullMessage的核心方法

判断brokerRole，master和slave工作模式的哪一种

判断MessageResult.status

如果responseCode是SUSCESS，判断是使用heap还是非heap方式传输数据

使用netty序列化response返回netty客户端

负载均衡

// AllocateMessageQueueAveragelypublic List
    
      allocate(String consumerGroup, String currentCID, List
     
       mqAll,                                       List
      
        cidAll) {    if (currentCID == null || currentCID.length() < 1) {        throw new IllegalArgumentException("currentCID is empty");    }    if (mqAll == null || mqAll.isEmpty()) {        throw new IllegalArgumentException("mqAll is null or mqAll empty");    }    if (cidAll == null || cidAll.isEmpty()) {        throw new IllegalArgumentException("cidAll is null or cidAll empty");    }    List
       
         result = new ArrayList
        
         ();    if (!cidAll.contains(currentCID)) {        log.info("[BUG] ConsumerGroup: {} The consumerId: {} not in cidAll: {}", //                consumerGroup, //                currentCID,//                cidAll);        return result;    }    int index = cidAll.indexOf(currentCID);    int mod = mqAll.size() % cidAll.size();    int averageSize =            mqAll.size() <= cidAll.size() ? 1 : (mod > 0 && index < mod ? mqAll.size() / cidAll.size()                    + 1 : mqAll.size() / cidAll.size());    int startIndex = (mod > 0 && index < mod) ? index * averageSize : index * averageSize + mod;    int range = Math.min(averageSize, mqAll.size() - startIndex);    for (int i = 0; i < range; i++) {        result.add(mqAll.get((startIndex + i) % mqAll.size()));    }    return result;}// RebalanceImplprivate boolean updateProcessQueueTableInRebalance(final String topic, final Set
         
           mqSet, final boolean isOrder) { boolean changed = false; // 去掉topic对应的无用MessageQueue（不包含在processQueueTable或者pullExpired） Iterator
          
           
            > it = this.processQueueTable.entrySet().iterator(); while (it.hasNext()) { Entry
            
              next = it.next(); MessageQueue mq = next.getKey(); ProcessQueue pq = next.getValue(); if (mq.getTopic().equals(topic)) { if (!mqSet.contains(mq)) { pq.setDropped(true); if (this.removeUnnecessaryMessageQueue(mq, pq)) { it.remove(); changed = true; log.info("doRebalance, {}, remove unnecessary mq, {}", consumerGroup, mq); } } else if (pq.isPullExpired()) { switch (this.consumeType()) { case CONSUME_ACTIVELY: break; case CONSUME_PASSIVELY: pq.setDropped(true); if (this.removeUnnecessaryMessageQueue(mq, pq)) { it.remove(); changed = true; log.error("[BUG]doRebalance, {}, remove unnecessary mq, {}, because pull is pause, so try to fixed it", consumerGroup, mq); } break; default: break; } } } } List
             
               pullRequestList = new ArrayList
              
               (); for (MessageQueue mq : mqSet) { // 如果MessageQueue不在processQueueTable if (!this.processQueueTable.containsKey(mq)) { if (isOrder && !this.lock(mq)) { log.warn("doRebalance, {}, add a new mq failed, {}, because lock failed", consumerGroup, mq); continue; } this.removeDirtyOffset(mq); ProcessQueue pq = new ProcessQueue(); long nextOffset = this.computePullFromWhere(mq); // 如果message还有数据需要读 if (nextOffset >= 0) { ProcessQueue pre = this.processQueueTable.putIfAbsent(mq, pq); if (pre != null) { log.info("doRebalance, {}, mq already exists, {}", consumerGroup, mq); } else { log.info("doRebalance, {}, add a new mq, {}", consumerGroup, mq); PullRequest pullRequest = new PullRequest(); pullRequest.setConsumerGroup(consumerGroup); pullRequest.setNextOffset(nextOffset); pullRequest.setMessageQueue(mq); pullRequest.setProcessQueue(pq); pullRequestList.add(pullRequest); changed = true; } } else { log.warn("doRebalance, {}, add new mq failed, {}", consumerGroup, mq); } } } // 将pullRequest放在pullRequestQueue中等待去取数据 this.dispatchPullRequest(pullRequestList); return changed;}

issue

多个consumer读取同一个consumerQueue的时候怎么记录每个读取的进度

每个consumer只要记住自己读取哪一个队列，以及offset就可以了

pull消息过程中的关键类

DefaultMQPushConsumerImpl

供DefaultMQPushConsumer调用，作为consumer的默认实现：

AllocateMessageQueueAveragely

这个类主要是consumer消费的负载均衡算法

public List
    
      allocate(String consumerGroup, String currentCID, List
     
       mqAll,                                       List
      
        cidAll) {    if (currentCID == null || currentCID.length() < 1) {        throw new IllegalArgumentException("currentCID is empty");    }    if (mqAll == null || mqAll.isEmpty()) {        throw new IllegalArgumentException("mqAll is null or mqAll empty");    }    if (cidAll == null || cidAll.isEmpty()) {        throw new IllegalArgumentException("cidAll is null or cidAll empty");    }    List
       
         result = new ArrayList
        
         ();    if (!cidAll.contains(currentCID)) {        log.info("[BUG] ConsumerGroup: {} The consumerId: {} not in cidAll: {}", //                consumerGroup, //                currentCID,//                cidAll);        return result;    }    // 基本原则，每个队列只能被一个consumer消费    // 当messageQueue个数小于等于consume的时候，排在前面（在list中的顺序）的consumer消费一个queue，index大于messageQueue之后的consumer消费不到queue，也就是为0    // 当messageQueue个数大于consumer的时候，分两种情况    //     当有余数（mod > 0）并且index < mod的时候，当前comsumer可以消费的队列个数是 mqAll.size() / cidAll.size() + 1    //     可以整除或者index 大于余数的时候，队列数为：mqAll.size() / cidAll.size()    int index = cidAll.indexOf(currentCID);    int mod = mqAll.size() % cidAll.size();    int averageSize =            mqAll.size() <= cidAll.size() ? 1 : (mod > 0 && index < mod ? mqAll.size() / cidAll.size()                    + 1 : mqAll.size() / cidAll.size());    int startIndex = (mod > 0 && index < mod) ? index * averageSize : index * averageSize + mod;    int range = Math.min(averageSize, mqAll.size() - startIndex);    for (int i = 0; i < range; i++) {        result.add(mqAll.get((startIndex + i) % mqAll.size()));    }    return result;}

转载于:https://www.cnblogs.com/sunshine-2015/p/6295100.html

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