Jafka学习之消息分区

     我们首先先来看下分区的定义：

 

   在接口上可以进行下面的操作： 

• 初始化操作
• 返回一个topic的所有partition
• 跟进brokerId返回broker
• 返回一个cluster中的所有的broker
• updateInfo方法是用来更新zk集群里面的数据结构
• close是做一些相关的资源关闭操作

Config类型的比较好理解，其实就是解析用户传递的相关配置文件，对brokerPartiions和allBrokers进行初始化。

比较难理解的是ZK方式，也就是集群模式下的相关配置，我们来仔细看下相关实现：

我们先来看下getZKTopicPartitionInfo方法的实现：

再看之前我们先来看下这个如何获得某个topic的partition数量，如果我们了解下面的存储结构，我们就大概了解了：

代理话题的注册

/brokers/topics/[topic]/[0...N] --> nPartions (ephemeral node)

 

每个代理会都要注册在某话题之下，注册后它会维护并保存该话题的分区总数。

上面的[topic]就是某个话题，0...N就是brokerId，这个路径里面存储的数据就是partition的数量，它是动态变化的，我们再来看代码，就非常明了。

private Map<String, SortedSet<Partition>> getZKTopicPartitionInfo() {
        // 创建一个结果集合，里面存放topic和partition之间的对应关系
        final Map<String, SortedSet<Partition>> brokerPartitionsPerTopic = new HashMap<String, SortedSet<Partition>>();
        // 保证路径 /brokers/topics 路径在zk上存在
        ZkUtils.makeSurePersistentPathExists( zkClient, ZkUtils.BrokerTopicsPath );
        // 获取 /brokers/topics 路径下的所有child，因为路径是/brokers/topics/[topic]
        List<String> topics = ZkUtils.getChildrenParentMayNotExist( zkClient, ZkUtils.BrokerTopicsPath );
        for (String topic : topics) {
            // find the number of broker partitions registered for this topic
            String brokerTopicPath = ZkUtils.BrokerTopicsPath + "/" + topic;
            // 获取到所有的partition，路径如下：/brokers/topics/[topic]/[0...N]
            List<String> brokerList = ZkUtils.getChildrenParentMayNotExist( zkClient, brokerTopicPath);
            //
            final SortedSet<Partition> sortedBrokerPartitions = new TreeSet<Partition>();
            for (String bid : brokerList) {
                final String numPath = brokerTopicPath + "/" + bid;
                final Integer numPartition = Integer.valueOf(ZkUtils.readData(zkClient , numPath));
                final int ibid = Integer.parseInt(bid);
                for (int i = 0; i < numPartition.intValue(); i++) {
                    sortedBrokerPartitions.add( new Partition(ibid, i));
                }
            }
            logger.debug("Broker ids and # of partitions on each for topic: " + topic + " = " + sortedBrokerPartitions);
            brokerPartitionsPerTopic.put(topic, sortedBrokerPartitions);
        }
        return brokerPartitionsPerTopic;
    }

      我们再来看获取所有broker的代码：

首先我们还是来看下broker的路径存储格式：

/brokers/ids/[0...N] --> host:port (ephemeral node)

如果再来看代码的话，就非常明白了：

    

private Map<Integer, Broker> getZKBrokerInfo() {
        Map<Integer, Broker> brokers = new HashMap<Integer, Broker>();
        List<String> allBrokersIds = ZkUtils.getChildrenParentMayNotExist( zkClient, ZkUtils.BrokerIdsPath );
        if (allBrokersIds != null) {
            logger.info("read all brokers count: " + allBrokersIds.size());
            for (String brokerId : allBrokersIds) {
                String brokerInfo = ZkUtils.readData(zkClient, ZkUtils. BrokerIdsPath + "/" + brokerId);
                Broker createBroker = Broker.createBroker(Integer.valueOf(brokerId), brokerInfo);
                brokers.put(Integer.valueOf(brokerId), createBroker);
                logger.info("Loading Broker " + createBroker);
            }
        }
        return brokers;
    }

 关于获取路径信息的相关就不进行多描述了，下来我们重点看下BrokerTopicListener这个类的实现：

下面讲解基于zookeeper的负载均衡的工作原理。它主要到下面的几个事件进行监听。

• 加入了新的代理
• 有一个代理下线了
• 注册了新的话题
• 代理注册了已有话题。

 

下面我们来仔细看看zk的watch函数：

class BrokerTopicsListener implements IZkChildListener {

        private Map<String, SortedSet<Partition>> originalBrokerTopicsParitions ;

        private Map<Integer, Broker> originBrokerIds;

        public BrokerTopicsListener(Map<String, SortedSet<Partition>> originalBrokerTopicsParitions,
                Map<Integer, Broker> originBrokerIds) {
            super();
            this.originalBrokerTopicsParitions = new LinkedHashMap<String, SortedSet<Partition>>(
                    originalBrokerTopicsParitions);
            this.originBrokerIds = new LinkedHashMap<Integer, Broker>(originBrokerIds);
            logger.debug("[BrokerTopicsListener] Creating broker topics listener to watch the following paths - \n" + "/broker/topics, /broker/topics/<topic>, /broker/<ids>");
            logger.debug("[BrokerTopicsListener] Initialized this broker topics listener with initial mapping of broker id to " + "partition id per topic with " + originalBrokerTopicsParitions);
        }

        public void handleChildChange(final String parentPath, List<String> currentChilds) throws Exception {
            final List<String> curChilds = currentChilds != null ? currentChilds : new ArrayList<String>();
            synchronized (zkWatcherLock ) {
                // 如果parentPath等于/brokers/topics
                if (ZkUtils.BrokerTopicsPath .equals(parentPath)) {
                    // 将之前的topic删除
                    Iterator<String> updatedTopics = curChilds.iterator();
                    while (updatedTopics.hasNext()) {
                        String t = updatedTopics.next();
                        if (originalBrokerTopicsParitions .containsKey(t)) {
                            updatedTopics.remove();
                        }
                    }
                    // 对于新创建的topic和相应的brokers绑定
                    for (String addedTopic : curChilds) {
                        String path = ZkUtils.BrokerTopicsPath + "/" + addedTopic;
                        List<String> brokerList = ZkUtils.getChildrenParentMayNotExist( zkClient, path);
                        processNewBrokerInExistingTopic(addedTopic, brokerList);
                        zkClient.subscribeChildChanges(ZkUtils.BrokerTopicsPath + "/" + addedTopic,
                                brokerTopicsListener);
                    }
                } else if (ZkUtils.BrokerIdsPath .equals(parentPath)) {
                    // 处理broker新增的情况
                    processBrokerChange(parentPath, curChilds);
                } else {
                    //check path: /brokers/topics/<topicname>
                    String[] ps = parentPath.split("/" );
                    if (ps.length == 4 && "topics".equals(ps[2])) {
                        logger.debug("[BrokerTopicsListener] List of brokers changed at " + parentPath + "\t Currently registered " + " list of brokers -> " + curChilds + " for topic -> " + ps[3]);
                        // broker的状态发生变化
                        processNewBrokerInExistingTopic(ps[3], curChilds);
                    }
                }
                //
                //update the data structures tracking older state values
                resetState();
            }
        }


        private void processBrokerChange(String parentPath, List<String> curChilds) {
            final Map<Integer, Broker> oldBrokerIdMap = new HashMap<Integer, Broker>(originBrokerIds );
            for (int i = curChilds.size() - 1; i >= 0; i--) {
                Integer brokerId = Integer.valueOf(curChilds.get(i));
                if (oldBrokerIdMap.remove(brokerId) != null) {//old topic
                    curChilds.remove(i); //remove old topics and left new topics
                }
            }
            //now curChilds are all new brokers
            //oldBrokerIdMap are all dead brokers
            for (String newBroker : curChilds) {
                final String brokerInfo = ZkUtils.readData(zkClient, ZkUtils. BrokerIdsPath + "/" + newBroker);
                String[] brokerHostPort = brokerInfo.split(":" );//format creatorId:host:port
                final Integer newBrokerId = Integer.valueOf(newBroker);
                final Broker broker = new Broker(newBrokerId.intValue(),//
                        brokerHostPort[1], //
                        brokerHostPort[1], //
                        Integer.parseInt(brokerHostPort[2]));
                allBrokers.put(newBrokerId, broker);
                callback.producerCbk(broker.id , broker.host, broker.port );
            }
            //
            //remove all dead broker and remove all broker-partition from topic list
            for (Map.Entry<Integer, Broker> deadBroker : oldBrokerIdMap.entrySet()) {
                //remove dead broker
                allBrokers.remove(deadBroker.getKey());

                //remove dead broker-partition from topic
                for (Map.Entry<String, SortedSet<Partition>> topicParition : topicBrokerPartitions.entrySet()) {
                    Iterator<Partition> partitions = topicParition.getValue().iterator();
                    while (partitions.hasNext()) {
                        Partition p = partitions.next();
                        if (deadBroker.getKey().intValue() == p.brokerId ) {
                            partitions.remove();
                        }
                    }
                }
            }
        }

        private void processNewBrokerInExistingTopic(String topic, List<String> brokerList) {

            SortedSet<Partition> updatedBrokerParts = getBrokerPartitions(zkClient, topic, brokerList);
            SortedSet<Partition> oldBrokerParts = topicBrokerPartitions.get(topic);
            SortedSet<Partition> mergedBrokerParts = new TreeSet<Partition>();
            if (oldBrokerParts != null) {
                mergedBrokerParts.addAll(oldBrokerParts);
            }
            //override old parts or add new parts
            mergedBrokerParts.addAll(updatedBrokerParts);
            //
            // keep only brokers that are alive
            Iterator<Partition> iter = mergedBrokerParts.iterator();
            while (iter.hasNext()) {
                if (!allBrokers.containsKey(iter.next().brokerId )) {
                    iter.remove();
                }
            }
            //            mergedBrokerParts = Sets.filter(mergedBrokerParts, new Predicate<Partition>() {
            //
            //                public boolean apply(Partition input) {
            //                    return allBrokers.containsKey(input.brokerId);
            //                }
            //            });
            topicBrokerPartitions.put(topic, mergedBrokerParts);
            logger.debug("[BrokerTopicsListener] List of broker partitions for topic: " + topic + " are " + mergedBrokerParts);
        }

        private void resetState() {
            logger.debug("[BrokerTopicsListener] Before reseting broker topic partitions state " + this.originalBrokerTopicsParitions );
            this.originalBrokerTopicsParitions = new HashMap<String, SortedSet<Partition>>(topicBrokerPartitions );
            logger.debug("[BrokerTopicsListener] After reseting broker topic partitions state " + originalBrokerTopicsParitions );
            //
            logger.debug("[BrokerTopicsListener] Before reseting broker id map state " + originBrokerIds);
            this.originBrokerIds = new HashMap<Integer, Broker>(allBrokers );
            logger.debug("[BrokerTopicsListener] After reseting broker id map state " + originBrokerIds);
        }
    }

    class ZKSessionExpirationListener implements IZkStateListener {

        public void handleNewSession() throws Exception {
            /**
             * When we get a SessionExpired event, we lost all ephemeral nodes and zkclient has
             * reestablished a connection for us.
             */
            logger.info("ZK expired; release old list of broker partitions for topics ");
            topicBrokerPartitions = getZKTopicPartitionInfo();
            allBrokers = getZKBrokerInfo();
            brokerTopicsListener.resetState();

            // register listener for change of brokers for each topic to keep topicsBrokerPartitions updated
            // NOTE: this is probably not required here. Since when we read from getZKTopicPartitionInfo() above,
            // it automatically recreates the watchers there itself
            for (String topic : topicBrokerPartitions.keySet()) {
                zkClient.subscribeChildChanges(ZkUtils.BrokerTopicsPath + "/" + topic, brokerTopicsListener);
            }
            // there is no need to re-register other listeners as they are listening on the child changes of
            // permanent nodes
        }

        public void handleStateChanged(KeeperState state) throws Exception {
        }
    }

    /**
     * Generate a mapping from broker id to (brokerId, numPartitions) for the list of brokers
     * specified
     *
     * @param topic the topic to which the brokers have registered
     * @param brokerList the list of brokers for which the partitions info is to be generated
     * @return a sequence of (brokerId, numPartitions) for brokers in brokerList
     */
    private static SortedSet<Partition> getBrokerPartitions(ZkClient zkClient, String topic, List<?> brokerList) {
        final String brokerTopicPath = ZkUtils.BrokerTopicsPath + "/" + topic;
        final SortedSet<Partition> brokerParts = new TreeSet<Partition>();
        for (Object brokerId : brokerList) {
            final Integer bid = Integer.valueOf(brokerId.toString());
            final Integer numPartition = Integer.valueOf(ZkUtils.readData(zkClient, brokerTopicPath + "/" + bid));
            for (int i = 0; i < numPartition.intValue(); i++) {
                brokerParts.add( new Partition(bid, i));
            }
        }
        return brokerParts;
    }