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RocketMQ(六)：nameserver与消息存储定位实现

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2021-02-02 08:28

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在rocketmq中，nameserver充当了一个配置管理者的角色，看起来好似不太重要。然而它是一个不或缺的角色，没有了它的存在，各个broker就是一盘散沙，各自为战。

所以，实际上，在rocketmq中，nameserver也是一个领导者的角色。它可以决定哪个消息存储到哪里，哪个broker干活或者上下线，在出现异常情况时，它要能够及时处理。以便让整个团队发挥应有的作用。nameserver相当于一个分布式系统的协调者。但是这个名字，是不是看起来很熟悉？请看后续！

1：为什么会有nameserver？

如文章开头所说，nameserver担任的，差不多是一个系统协调者这么个角色。那么，我们知道，在分布式协调工作方面，有很多现成的组件可用。比如 zookeeper, 那么为什么还要自己搞一套nameserver出来？是为了刷存在感？

对于为什么不选择zk之类的组件实现协调者角色，初衷如何我们不得而知。但至少有几个可知答案可以做下支撑：（以zk为例）

　　　　1. zk存在大量的集群间通信；
　　　　2. zk是一个比较重的组件，而本身就作为消息中间的mq，则最好不好另外再依赖其他组件；（个人感觉）
　　　　3. zk对于数据的固化能力比较弱，配置往往受限于zk的数据格式；

总体来说，可能就是rocketmq想要做的功能在zk上不太好做，或者做起来也费劲，或者太重，索性就不要搞了。自己搞一个完全定制化的好了。事实上，rocketmq的nameserver也实现得相当简单轻量。这也是设计者的初衷吧。

2. nameserver的启动流程解析

一般地，一个框架级别的服务启动，还是有些复杂的，那样的话，我们懒得去看其具体过程。但前面说了，nameserver实现得非常轻量级，所以，其启动也就相当简单。所以，我们可以快速一览其过程。　　整个nameserver的启动类是 org.apache.rocketmq.namesrv.NamesrvStartup, 工作过程大致如下：

// 入口main    public static void main(String[] args) {        main0(args);    }
    public static NamesrvController main0(String[] args) {        try {            // 创建本服务的核心控制器, 解析各种配置参数，默认值之类的            NamesrvController controller = createNamesrvController(args);            // 开启服务, 如打开            start(controller);            String tip = "The Name Server boot success. serializeType=" + RemotingCommand.getSerializeTypeConfigInThisServer();            log.info(tip);            System.out.printf("%s%n", tip);            return controller;        } catch (Throwable e) {            e.printStackTrace();            System.exit(-1);        }
        return null;    }

所以整个启动过程，基本就是一个 Controller 搞定了，你说不简单吗？额，也许不一定！整个创建 Controller 的过程就是解析参数的过程，有兴趣可以打开如下代码看看：

 public static NamesrvController createNamesrvController(String[] args) throws IOException, JoranException {        System.setProperty(RemotingCommand.REMOTING_VERSION_KEY, Integer.toString(MQVersion.CURRENT_VERSION));        //PackageConflictDetect.detectFastjson();
        Options options = ServerUtil.buildCommandlineOptions(new Options());        commandLine = ServerUtil.parseCmdLine("mqnamesrv", args, buildCommandlineOptions(options), new PosixParser());        if (null == commandLine) {            System.exit(-1);            return null;        }
        final NamesrvConfig namesrvConfig = new NamesrvConfig();        final NettyServerConfig nettyServerConfig = new NettyServerConfig();        nettyServerConfig.setListenPort(9876);        // -c xx.properties 用于指定配置文件，优先级较低        if (commandLine.hasOption('c')) {            String file = commandLine.getOptionValue('c');            if (file != null) {                InputStream in = new BufferedInputStream(new FileInputStream(file));                properties = new Properties();                properties.load(in);                MixAll.properties2Object(properties, namesrvConfig);                MixAll.properties2Object(properties, nettyServerConfig);
                namesrvConfig.setConfigStorePath(file);
                System.out.printf("load config properties file OK, %s%n", file);                in.close();            }        }        // -p 仅为打印查看启动参数        if (commandLine.hasOption('p')) {            InternalLogger console = InternalLoggerFactory.getLogger(LoggerName.NAMESRV_CONSOLE_NAME);            MixAll.printObjectProperties(console, namesrvConfig);            MixAll.printObjectProperties(console, nettyServerConfig);            System.exit(0);        }
        MixAll.properties2Object(ServerUtil.commandLine2Properties(commandLine), namesrvConfig);
        if (null == namesrvConfig.getRocketmqHome()) {            System.out.printf("Please set the %s variable in your environment to match the location of the RocketMQ installation%n", MixAll.ROCKETMQ_HOME_ENV);            System.exit(-2);        }
        LoggerContext lc = (LoggerContext) LoggerFactory.getILoggerFactory();        JoranConfigurator configurator = new JoranConfigurator();        configurator.setContext(lc);        lc.reset();        configurator.doConfigure(namesrvConfig.getRocketmqHome() + "/conf/logback_namesrv.xml");
        log = InternalLoggerFactory.getLogger(LoggerName.NAMESRV_LOGGER_NAME);
        MixAll.printObjectProperties(log, namesrvConfig);        MixAll.printObjectProperties(log, nettyServerConfig);        // 将配置参数传入controller构造实例        final NamesrvController controller = new NamesrvController(namesrvConfig, nettyServerConfig);
        // remember all configs to prevent discard        controller.getConfiguration().registerConfig(properties);
        return controller;    }    // Controller 构造方法    // org.apache.rocketmq.namesrv.NamesrvController#NamesrvController    public NamesrvController(NamesrvConfig namesrvConfig, NettyServerConfig nettyServerConfig) {        this.namesrvConfig = namesrvConfig;        this.nettyServerConfig = nettyServerConfig;        this.kvConfigManager = new KVConfigManager(this);        this.routeInfoManager = new RouteInfoManager();        this.brokerHousekeepingService = new BrokerHousekeepingService(this);        this.configuration = new Configuration(            log,            this.namesrvConfig, this.nettyServerConfig        );        this.configuration.setStorePathFromConfig(this.namesrvConfig, "configStorePath");    }    // org.apache.rocketmq.common.Configuration#registerConfig    /**     * register config properties     *     * @return the current Configuration object     */    public Configuration registerConfig(Properties extProperties) {        if (extProperties == null) {            return this;        }
        try {            readWriteLock.writeLock().lockInterruptibly();
            try {                merge(extProperties, this.allConfigs);            } finally {                readWriteLock.writeLock().unlock();            }        } catch (InterruptedException e) {            log.error("register lock error. {}" + extProperties);        }
        return this;    }

接下来，我们主要来看看这start()过程到底如何，复杂性必然都在这里了。

 // org.apache.rocketmq.namesrv.NamesrvStartup#start    public static NamesrvController start(final NamesrvController controller) throws Exception {
        if (null == controller) {            throw new IllegalArgumentException("NamesrvController is null");        }        // 初始化controller各环境，如果失败，则退出启动        boolean initResult = controller.initialize();        if (!initResult) {            controller.shutdown();            System.exit(-3);        }        // 注册一个关闭钩子        Runtime.getRuntime().addShutdownHook(new ShutdownHookThread(log, new Callable() {            @Override            public Void call() throws Exception {                controller.shutdown();                return null;            }        }));        // 核心start()方法        controller.start();
        return controller;    }    // org.apache.rocketmq.namesrv.NamesrvController#initialize    public boolean initialize() {
        this.kvConfigManager.load();
        this.remotingServer = new NettyRemotingServer(this.nettyServerConfig, this.brokerHousekeepingService);
        this.remotingExecutor =            Executors.newFixedThreadPool(nettyServerConfig.getServerWorkerThreads(), new ThreadFactoryImpl("RemotingExecutorThread_"));        // 注册处理器        this.registerProcessor();        // 启动后台扫描线程，扫描掉线的broker        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
            @Override            public void run() {                NamesrvController.this.routeInfoManager.scanNotActiveBroker();            }        }, 5, 10, TimeUnit.SECONDS);        // 打印日志定时任务        this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
            @Override            public void run() {                NamesrvController.this.kvConfigManager.printAllPeriodically();            }        }, 1, 10, TimeUnit.MINUTES);
        if (TlsSystemConfig.tlsMode != TlsMode.DISABLED) {            // Register a listener to reload SslContext            try {                fileWatchService = new FileWatchService(                    new String[] {                        TlsSystemConfig.tlsServerCertPath,                        TlsSystemConfig.tlsServerKeyPath,                        TlsSystemConfig.tlsServerTrustCertPath                    },                    new FileWatchService.Listener() {                        boolean certChanged, keyChanged = false;                        @Override                        public void onChanged(String path) {                            if (path.equals(TlsSystemConfig.tlsServerTrustCertPath)) {                                log.info("The trust certificate changed, reload the ssl context");                                reloadServerSslContext();                            }                            if (path.equals(TlsSystemConfig.tlsServerCertPath)) {                                certChanged = true;                            }                            if (path.equals(TlsSystemConfig.tlsServerKeyPath)) {                                keyChanged = true;                            }                            if (certChanged && keyChanged) {                                log.info("The certificate and private key changed, reload the ssl context");                                certChanged = keyChanged = false;                                reloadServerSslContext();                            }                        }                        private void reloadServerSslContext() {                            ((NettyRemotingServer) remotingServer).loadSslContext();                        }                    });            } catch (Exception e) {                log.warn("FileWatchService created error, can't load the certificate dynamically");            }        }        // no false        return true;    }    private void registerProcessor() {        if (namesrvConfig.isClusterTest()) {
            this.remotingServer.registerDefaultProcessor(new ClusterTestRequestProcessor(this, namesrvConfig.getProductEnvName()),                this.remotingExecutor);        } else {            // 只会有一个处理器处理业务            this.remotingServer.registerDefaultProcessor(new DefaultRequestProcessor(this), this.remotingExecutor);        }    }
    // 初始化完成后，接下来是 start() 方法    // org.apache.rocketmq.namesrv.NamesrvController#start    public void start() throws Exception {        // 开启后台端口服务，nameserver可连接        this.remotingServer.start();        // 文件检测线程        if (this.fileWatchService != null) {            this.fileWatchService.start();        }    }

可见，controller的启动过程也非常简单，就是设置好各初始实例，开几个后台定时任务，注册处理器，然后将tcp端口打开，即可。其中端口服务是使用netty作为通信组件，其操作完全遵从netty编程范式。可自行查阅。

@Override    public void start() {        this.defaultEventExecutorGroup = new DefaultEventExecutorGroup(            nettyServerConfig.getServerWorkerThreads(),            new ThreadFactory() {
                private AtomicInteger threadIndex = new AtomicInteger(0);
                @Override                public Thread newThread(Runnable r) {                    return new Thread(r, "NettyServerCodecThread_" + this.threadIndex.incrementAndGet());                }            });
        prepareSharableHandlers();
        ServerBootstrap childHandler =            this.serverBootstrap.group(this.eventLoopGroupBoss, this.eventLoopGroupSelector)                .channel(useEpoll() ? EpollServerSocketChannel.class : NioServerSocketChannel.class)                .option(ChannelOption.SO_BACKLOG, 1024)                .option(ChannelOption.SO_REUSEADDR, true)                .option(ChannelOption.SO_KEEPALIVE, false)                .childOption(ChannelOption.TCP_NODELAY, true)                .childOption(ChannelOption.SO_SNDBUF, nettyServerConfig.getServerSocketSndBufSize())                .childOption(ChannelOption.SO_RCVBUF, nettyServerConfig.getServerSocketRcvBufSize())                .localAddress(new InetSocketAddress(this.nettyServerConfig.getListenPort()))                .childHandler(new ChannelInitializer() {                    @Override                    public void initChannel(SocketChannel ch) throws Exception {                        ch.pipeline()                            .addLast(defaultEventExecutorGroup, HANDSHAKE_HANDLER_NAME, handshakeHandler)                            .addLast(defaultEventExecutorGroup,                                encoder,                                new NettyDecoder(),                                new IdleStateHandler(0, 0, nettyServerConfig.getServerChannelMaxIdleTimeSeconds()),                                connectionManageHandler,                                serverHandler                            );                    }                });
        if (nettyServerConfig.isServerPooledByteBufAllocatorEnable()) {            childHandler.childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT);        }
        try {            ChannelFuture sync = this.serverBootstrap.bind().sync();            InetSocketAddress addr = (InetSocketAddress) sync.channel().localAddress();            this.port = addr.getPort();        } catch (InterruptedException e1) {            throw new RuntimeException("this.serverBootstrap.bind().sync() InterruptedException", e1);        }
        if (this.channelEventListener != null) {            this.nettyEventExecutor.start();        }
        this.timer.scheduleAtFixedRate(new TimerTask() {
            @Override            public void run() {                try {                    NettyRemotingServer.this.scanResponseTable();                } catch (Throwable e) {                    log.error("scanResponseTable exception", e);                }            }        }, 1000 * 3, 1000);    }

至此，nameserver的启动流程就完成了，果然是轻量级。至于其提供什么样的服务，我们下一节再讲。

3. nameserver 业务处理框架

因nameserver和broker一样，都共用了remoting模块的代码，即都依赖于netty的handler处理机制。所以其处理器入口都是一样的。反正最终都是找到对应的processor, 然后处理业务即可。此处，nameserver只会提供一个默认的处理器，即DefaultRequestProcessor。所以，只需了解其processRequest()即可知nameserver的整体能力了。

// org.apache.rocketmq.namesrv.processor.DefaultRequestProcessor#processRequest    @Override    public RemotingCommand processRequest(ChannelHandlerContext ctx,        RemotingCommand request) throws RemotingCommandException {
        if (ctx != null) {            log.debug("receive request, {} {} {}",                request.getCode(),                RemotingHelper.parseChannelRemoteAddr(ctx.channel()),                request);        }
        switch (request.getCode()) {            case RequestCode.PUT_KV_CONFIG:                return this.putKVConfig(ctx, request);            case RequestCode.GET_KV_CONFIG:                return this.getKVConfig(ctx, request);            case RequestCode.DELETE_KV_CONFIG:                return this.deleteKVConfig(ctx, request);            case RequestCode.QUERY_DATA_VERSION:                return queryBrokerTopicConfig(ctx, request);            // 注册broker信息，这种操作一般是在broker启动的时候进行请求            case RequestCode.REGISTER_BROKER:                Version brokerVersion = MQVersion.value2Version(request.getVersion());                if (brokerVersion.ordinal() >= MQVersion.Version.V3_0_11.ordinal()) {                    return this.registerBrokerWithFilterServer(ctx, request);                } else {                    return this.registerBroker(ctx, request);                }            // 下线broker            case RequestCode.UNREGISTER_BROKER:                return this.unregisterBroker(ctx, request);            // 获取路由信息，即哪个topic存在于哪些broker上，哪些messageQueue在哪里等            case RequestCode.GET_ROUTEINFO_BY_TOPIC:                return this.getRouteInfoByTopic(ctx, request);            case RequestCode.GET_BROKER_CLUSTER_INFO:                return this.getBrokerClusterInfo(ctx, request);            case RequestCode.WIPE_WRITE_PERM_OF_BROKER:                return this.wipeWritePermOfBroker(ctx, request);            case RequestCode.GET_ALL_TOPIC_LIST_FROM_NAMESERVER:                return getAllTopicListFromNameserver(ctx, request);            case RequestCode.DELETE_TOPIC_IN_NAMESRV:                return deleteTopicInNamesrv(ctx, request);            case RequestCode.GET_KVLIST_BY_NAMESPACE:                return this.getKVListByNamespace(ctx, request);            case RequestCode.GET_TOPICS_BY_CLUSTER:                return this.getTopicsByCluster(ctx, request);            case RequestCode.GET_SYSTEM_TOPIC_LIST_FROM_NS:                return this.getSystemTopicListFromNs(ctx, request);            case RequestCode.GET_UNIT_TOPIC_LIST:                return this.getUnitTopicList(ctx, request);            case RequestCode.GET_HAS_UNIT_SUB_TOPIC_LIST:                return this.getHasUnitSubTopicList(ctx, request);            case RequestCode.GET_HAS_UNIT_SUB_UNUNIT_TOPIC_LIST:                return this.getHasUnitSubUnUnitTopicList(ctx, request);            case RequestCode.UPDATE_NAMESRV_CONFIG:                return this.updateConfig(ctx, request);            case RequestCode.GET_NAMESRV_CONFIG:                return this.getConfig(ctx, request);            default:                break;        }        return null;    }


以上就是整个nameserver提供的服务列表了，也没啥注释，见字如悟吧，我们也不想过多纠缠。但总体上，其处理的业务类型并不多，主要有三类：

　　　　1. 配置信息kv的操作；
　　　　2. broker上下线管理操作；
　　　　3. topic路由信息管理服务；

各自实现当然是按照业务处理，本无需多说，但为了解概要，我们还是挑一个重点来说说吧：broker的上线处理注册：

// 为保持前沿起见，咱们以高版本服务展开思路（即版本大于3.0.11）    public RemotingCommand registerBrokerWithFilterServer(ChannelHandlerContext ctx, RemotingCommand request)        throws RemotingCommandException {        final RemotingCommand response = RemotingCommand.createResponseCommand(RegisterBrokerResponseHeader.class);        final RegisterBrokerResponseHeader responseHeader = (RegisterBrokerResponseHeader) response.readCustomHeader();        final RegisterBrokerRequestHeader requestHeader =            (RegisterBrokerRequestHeader) request.decodeCommandCustomHeader(RegisterBrokerRequestHeader.class);
        if (!checksum(ctx, request, requestHeader)) {            response.setCode(ResponseCode.SYSTEM_ERROR);            response.setRemark("crc32 not match");            return response;        }
        RegisterBrokerBody registerBrokerBody = new RegisterBrokerBody();
        if (request.getBody() != null) {            try {                registerBrokerBody = RegisterBrokerBody.decode(request.getBody(), requestHeader.isCompressed());            } catch (Exception e) {                throw new RemotingCommandException("Failed to decode RegisterBrokerBody", e);            }        } else {            registerBrokerBody.getTopicConfigSerializeWrapper().getDataVersion().setCounter(new AtomicLong(0));            registerBrokerBody.getTopicConfigSerializeWrapper().getDataVersion().setTimestamp(0);        }        // 重点实现: registerBroker        RegisterBrokerResult result = this.namesrvController.getRouteInfoManager().registerBroker(            requestHeader.getClusterName(),            requestHeader.getBrokerAddr(),            requestHeader.getBrokerName(),            requestHeader.getBrokerId(),            requestHeader.getHaServerAddr(),            registerBrokerBody.getTopicConfigSerializeWrapper(),            registerBrokerBody.getFilterServerList(),            ctx.channel());
        responseHeader.setHaServerAddr(result.getHaServerAddr());        responseHeader.setMasterAddr(result.getMasterAddr());
        byte[] jsonValue = this.namesrvController.getKvConfigManager().getKVListByNamespace(NamesrvUtil.NAMESPACE_ORDER_TOPIC_CONFIG);        response.setBody(jsonValue);
        response.setCode(ResponseCode.SUCCESS);        response.setRemark(null);        return response;    }    // org.apache.rocketmq.namesrv.routeinfo.RouteInfoManager#registerBroker    public RegisterBrokerResult registerBroker(        final String clusterName,        final String brokerAddr,        final String brokerName,        final long brokerId,        final String haServerAddr,        final TopicConfigSerializeWrapper topicConfigWrapper,        final List filterServerList,        final Channel channel) {        RegisterBrokerResult result = new RegisterBrokerResult();        try {            try {                // 上锁更新各表数据                this.lock.writeLock().lockInterruptibly();                // 集群名表                Set brokerNames = this.clusterAddrTable.get(clusterName);                if (null == brokerNames) {                    brokerNames = new HashSet();                    this.clusterAddrTable.put(clusterName, brokerNames);                }                brokerNames.add(brokerName);
                boolean registerFirst = false;                // broker详细信息表                BrokerData brokerData = this.brokerAddrTable.get(brokerName);                if (null == brokerData) {                    registerFirst = true;                    brokerData = new BrokerData(clusterName, brokerName, new HashMap());                    this.brokerAddrTable.put(brokerName, brokerData);                }                Map brokerAddrsMap = brokerData.getBrokerAddrs();                //Switch slave to master: first remove <1, IP:PORT> in namesrv, then add <0, IP:PORT>                //The same IP:PORT must only have one record in brokerAddrTable                Iterator> it = brokerAddrsMap.entrySet().iterator();                while (it.hasNext()) {                    Entry item = it.next();                    if (null != brokerAddr && brokerAddr.equals(item.getValue()) && brokerId != item.getKey()) {                        it.remove();                    }                }
                String oldAddr = brokerData.getBrokerAddrs().put(brokerId, brokerAddr);                registerFirst = registerFirst || (null == oldAddr);
                if (null != topicConfigWrapper                    && MixAll.MASTER_ID == brokerId) {                    if (this.isBrokerTopicConfigChanged(brokerAddr, topicConfigWrapper.getDataVersion())                        || registerFirst) {                        // 首次注册或者topic变更，则更新topic信息                        ConcurrentMap tcTable =                            topicConfigWrapper.getTopicConfigTable();                        if (tcTable != null) {                            for (Map.Entry entry : tcTable.entrySet()) {                                this.createAndUpdateQueueData(brokerName, entry.getValue());                            }                        }                    }                }                // 存活的broker信息表                BrokerLiveInfo prevBrokerLiveInfo = this.brokerLiveTable.put(brokerAddr,                    new BrokerLiveInfo(                        System.currentTimeMillis(),                        topicConfigWrapper.getDataVersion(),                        channel,                        haServerAddr));                if (null == prevBrokerLiveInfo) {                    log.info("new broker registered, {} HAServer: {}", brokerAddr, haServerAddr);                }
                if (filterServerList != null) {                    if (filterServerList.isEmpty()) {                        this.filterServerTable.remove(brokerAddr);                    } else {                        this.filterServerTable.put(brokerAddr, filterServerList);                    }                }                // slave节点注册需绑定masterAddr 返回                if (MixAll.MASTER_ID != brokerId) {                    String masterAddr = brokerData.getBrokerAddrs().get(MixAll.MASTER_ID);                    if (masterAddr != null) {                        BrokerLiveInfo brokerLiveInfo = this.brokerLiveTable.get(masterAddr);                        if (brokerLiveInfo != null) {                            result.setHaServerAddr(brokerLiveInfo.getHaServerAddr());                            result.setMasterAddr(masterAddr);                        }                    }                }            } finally {                this.lock.writeLock().unlock();            }        } catch (Exception e) {            log.error("registerBroker Exception", e);        }
        return result;    }

好吧，是不是很抽象。没关系，能知道大概意思就行了。大体上就是broker上线了，nameserver需要知道这些事，要把这信息加入到各表项中，以备将来使用。具体理解我们应该要从业务性质出发才能透彻。反正就和咱们平时写业务代码并无二致。

4. topic存储位置策略

nameserver除了有注册broker的核心作用外，还有一个非常核心的作用就是，为各消费者或生产者提供各topic信息所在位置。这个位置决定了数据如何存储以及如何访问问题，只要这个决策出问题，则整个集群的可靠性就无法保证了。所以，这个点需要我们深入理解下。

在kafka中，其存储策略是和shard强相关的，一个topic分配了多少shard就决定了它可以存储到几个机器节点上，即kafka是以shard作为粒度分配存储的。

但rocketmq中则不太一样，类似的概念有：topic是最外层的存储，而messageQueue则是内一层的存储，它是否是按照topic存储或者按照msgQueue存在呢？实际上，在官方文档中，已经描述清楚了：Broker 在实际部署过程中对应一台服务器，每个 Broker 可以存储多个Topic的消息，每个Topic的消息也可以分片存储于不同的 Broker。Message Queue 用于存储消息的物理地址，每个Topic中的消息地址存储于多个 Message Queue 中。

即rocketmq中是以message queue作为最细粒度的存储的，实际上这基本无悬念，因为分布式存储需要。（试想以topic为存储粒度会带来多少问题就知道了）

那么，它又是如何划分哪个message queue存储在哪里的呢？

 // RequestCode.GET_ROUTEINFO_BY_TOPIC    public RemotingCommand getRouteInfoByTopic(ChannelHandlerContext ctx,        RemotingCommand request) throws RemotingCommandException {        final RemotingCommand response = RemotingCommand.createResponseCommand(null);        final GetRouteInfoRequestHeader requestHeader =            (GetRouteInfoRequestHeader) request.decodeCommandCustomHeader(GetRouteInfoRequestHeader.class);        // 获取topic路由信息        TopicRouteData topicRouteData = this.namesrvController.getRouteInfoManager().pickupTopicRouteData(requestHeader.getTopic());
        if (topicRouteData != null) {            // 顺序消费配置            if (this.namesrvController.getNamesrvConfig().isOrderMessageEnable()) {                String orderTopicConf =                    this.namesrvController.getKvConfigManager().getKVConfig(NamesrvUtil.NAMESPACE_ORDER_TOPIC_CONFIG,                        requestHeader.getTopic());                topicRouteData.setOrderTopicConf(orderTopicConf);            }
            byte[] content = topicRouteData.encode();            response.setBody(content);            response.setCode(ResponseCode.SUCCESS);            response.setRemark(null);            return response;        }
        response.setCode(ResponseCode.TOPIC_NOT_EXIST);        response.setRemark("No topic route info in name server for the topic: " + requestHeader.getTopic()            + FAQUrl.suggestTodo(FAQUrl.APPLY_TOPIC_URL));        return response;    }    // org.apache.rocketmq.namesrv.routeinfo.RouteInfoManager#pickupTopicRouteData    public TopicRouteData pickupTopicRouteData(final String topic) {        TopicRouteData topicRouteData = new TopicRouteData();        boolean foundQueueData = false;        boolean foundBrokerData = false;        Set brokerNameSet = new HashSet();        List brokerDataList = new LinkedList();        topicRouteData.setBrokerDatas(brokerDataList);
        HashMap> filterServerMap = new HashMap>();        topicRouteData.setFilterServerTable(filterServerMap);
        try {            try {                this.lock.readLock().lockInterruptibly();                // 获取所有topic的messageQueue信息                List queueDataList = this.topicQueueTable.get(topic);                if (queueDataList != null) {                    topicRouteData.setQueueDatas(queueDataList);                    foundQueueData = true;
                    Iterator it = queueDataList.iterator();                    while (it.hasNext()) {                        QueueData qd = it.next();                        brokerNameSet.add(qd.getBrokerName());                    }                    // 根据brokerName, 查找broker信息，如果没找到说明该broker可能已经下线，不能算在路由信息内                    for (String brokerName : brokerNameSet) {                        BrokerData brokerData = this.brokerAddrTable.get(brokerName);                        if (null != brokerData) {                            BrokerData brokerDataClone = new BrokerData(brokerData.getCluster(), brokerData.getBrokerName(), (HashMap) brokerData                                .getBrokerAddrs().clone());                            brokerDataList.add(brokerDataClone);                            // 只要找到一个broker就可以进行路由处理                            foundBrokerData = true;                            for (final String brokerAddr : brokerDataClone.getBrokerAddrs().values()) {                                List filterServerList = this.filterServerTable.get(brokerAddr);                                filterServerMap.put(brokerAddr, filterServerList);                            }                        }                    }                }            } finally {                this.lock.readLock().unlock();            }        } catch (Exception e) {            log.error("pickupTopicRouteData Exception", e);        }
        log.debug("pickupTopicRouteData {} {}", topic, topicRouteData);        // 只有队列信息和broker信息都找到时，整个路由信息才可返回        if (foundBrokerData && foundQueueData) {            return topicRouteData;        }
        return null;    }    // QueueData 作为路由信息的重要组成部分，其数据结构如下public class QueueData implements Comparable {    private String brokerName;    private int readQueueNums;    private int writeQueueNums;    private int perm;    private int topicSynFlag;    ...}    // brokerData 数据结构如下public class BrokerData implements Comparable {    private String cluster;    private String brokerName;    private HashMap brokerAddrs;    ...}


ok, 从上面的实现中，我们可以看到，查找路由信息，是根据topic进行查找的。而topic信息保存在 topicQueueTable 中。这里有个重要点是，整个路由查找过程，居然和queueId是无关的，那么它又是如何定位queueId所在的位置呢？另外，这个topicQueTable里的数据又是何时维护的呢？

首先，对于topicQueueTable的维护，是在broker注册和解注册时维护的，这很好理解。

 // 也就前面看到的broker为master节点时的 createAndUpdateQueueData()    private void createAndUpdateQueueData(final String brokerName, final TopicConfig topicConfig) {        QueueData queueData = new QueueData();        queueData.setBrokerName(brokerName);        queueData.setWriteQueueNums(topicConfig.getWriteQueueNums());        queueData.setReadQueueNums(topicConfig.getReadQueueNums());        queueData.setPerm(topicConfig.getPerm());        queueData.setTopicSynFlag(topicConfig.getTopicSysFlag());
        List queueDataList = this.topicQueueTable.get(topicConfig.getTopicName());        // topic的首个broker        if (null == queueDataList) {            queueDataList = new LinkedList();            queueDataList.add(queueData);            this.topicQueueTable.put(topicConfig.getTopicName(), queueDataList);            log.info("new topic registered, {} {}", topicConfig.getTopicName(), queueData);        } else {            boolean addNewOne = true;
            Iterator it = queueDataList.iterator();            // 添加一个broker            while (it.hasNext()) {                QueueData qd = it.next();                if (qd.getBrokerName().equals(brokerName)) {                    if (qd.equals(queueData)) {                        addNewOne = false;                    } else {                        log.info("topic changed, {} OLD: {} NEW: {}", topicConfig.getTopicName(), qd,                            queueData);                        it.remove();                    }                }            }
            if (addNewOne) {                queueDataList.add(queueData);            }        }    }

但针对queueId又是何时进行处理的呢？看起来nameserver不得而知。

事实上，数据发送到哪个broker或从哪个broker上进行数据消费，是由各客户端根据策略决定的。比如在producer中是这样处理的：

// org.apache.rocketmq.client.impl.producer.DefaultMQProducerImpl#sendDefaultImpl    private SendResult sendDefaultImpl(        Message msg,        final CommunicationMode communicationMode,        final SendCallback sendCallback,        final long timeout    ) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {        this.makeSureStateOK();        Validators.checkMessage(msg, this.defaultMQProducer);        final long invokeID = random.nextLong();        long beginTimestampFirst = System.currentTimeMillis();        long beginTimestampPrev = beginTimestampFirst;        long endTimestamp = beginTimestampFirst;        // 此处即是nameserver返回的路由信息，即可用的broker列表        TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());        if (topicPublishInfo != null && topicPublishInfo.ok()) {            boolean callTimeout = false;            MessageQueue mq = null;            Exception exception = null;            SendResult sendResult = null;            int timesTotal = communicationMode == CommunicationMode.SYNC ? 1 + this.defaultMQProducer.getRetryTimesWhenSendFailed() : 1;            int times = 0;            String[] brokersSent = new String[timesTotal];            for (; times < timesTotal; times++) {                // 首次进入时，只是选择一个队列发送                String lastBrokerName = null == mq ? null : mq.getBrokerName();                MessageQueue mqSelected = this.selectOneMessageQueue(topicPublishInfo, lastBrokerName);                if (mqSelected != null) {                    mq = mqSelected;                    brokersSent[times] = mq.getBrokerName();                    try {                        beginTimestampPrev = System.currentTimeMillis();                        if (times > 0) {                            //Reset topic with namespace during resend.                            msg.setTopic(this.defaultMQProducer.withNamespace(msg.getTopic()));                        }                        long costTime = beginTimestampPrev - beginTimestampFirst;                        if (timeout < costTime) {                            callTimeout = true;                            break;                        }                        // 向选择出来的messageQueue 发送消息数据                        sendResult = this.sendKernelImpl(msg, mq, communicationMode, sendCallback, topicPublishInfo, timeout - costTime);                        endTimestamp = System.currentTimeMillis();                        this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false);                        switch (communicationMode) {                            case ASYNC:                                return null;                            case ONEWAY:                                return null;                            case SYNC:                                if (sendResult.getSendStatus() != SendStatus.SEND_OK) {                                    if (this.defaultMQProducer.isRetryAnotherBrokerWhenNotStoreOK()) {                                        continue;                                    }                                }
                                return sendResult;                            default:                                break;                        }                    } catch (RemotingException e)                     ...    }    // org.apache.rocketmq.client.impl.producer.DefaultMQProducerImpl#selectOneMessageQueue    public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {        return this.mqFaultStrategy.selectOneMessageQueue(tpInfo, lastBrokerName);    }    // org.apache.rocketmq.client.latency.MQFaultStrategy#selectOneMessageQueue    public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {        // 容错处理，不影响策略理解        if (this.sendLatencyFaultEnable) {            try {                int index = tpInfo.getSendWhichQueue().getAndIncrement();                for (int i = 0; i < tpInfo.getMessageQueueList().size(); i++) {                    int pos = Math.abs(index++) % tpInfo.getMessageQueueList().size();                    if (pos < 0)                        pos = 0;                    MessageQueue mq = tpInfo.getMessageQueueList().get(pos);                    if (latencyFaultTolerance.isAvailable(mq.getBrokerName())) {                        if (null == lastBrokerName || mq.getBrokerName().equals(lastBrokerName))                            return mq;                    }                }
                final String notBestBroker = latencyFaultTolerance.pickOneAtLeast();                int writeQueueNums = tpInfo.getQueueIdByBroker(notBestBroker);                if (writeQueueNums > 0) {                    final MessageQueue mq = tpInfo.selectOneMessageQueue();                    if (notBestBroker != null) {                        mq.setBrokerName(notBestBroker);                        mq.setQueueId(tpInfo.getSendWhichQueue().getAndIncrement() % writeQueueNums);                    }                    return mq;                } else {                    latencyFaultTolerance.remove(notBestBroker);                }            } catch (Exception e) {                log.error("Error occurred when selecting message queue", e);            }
            return tpInfo.selectOneMessageQueue();        }
        return tpInfo.selectOneMessageQueue(lastBrokerName);    }    // org.apache.rocketmq.client.impl.producer.TopicPublishInfo#selectOneMessageQueue    // 直接使用轮询的方式选择一个队列     public MessageQueue selectOneMessageQueue(final String lastBrokerName) {        if (lastBrokerName == null) {            // 任意选择一个messageQueue作为发送目标            return selectOneMessageQueue();        } else {            int index = this.sendWhichQueue.getAndIncrement();            // 最大尝试n次获取不一样的MQueue, 如仍然获取不到，则随便选择一个即可            for (int i = 0; i < this.messageQueueList.size(); i++) {                int pos = Math.abs(index++) % this.messageQueueList.size();                if (pos < 0)                    pos = 0;                MessageQueue mq = this.messageQueueList.get(pos);                if (!mq.getBrokerName().equals(lastBrokerName)) {                    return mq;                }            }            return selectOneMessageQueue();        }    }

好了，通过上面的描述，我们大概知道了，一个消息要发送往消息server时，首先会根据topic找到所有可用的broker列表（nameserver提供），然后根据一个所谓策略选择一个MessageQueue，最后向这个MessageQueue发送数据即可。所以，这个MessageQueue是非常重要的，我们来看下其数据结构：

// org.apache.rocketmq.common.message.MessageQueuepublic class MessageQueue implements Comparable, Serializable {    private static final long serialVersionUID = 6191200464116433425L;    private String topic;    private String brokerName;    private int queueId;    ...}


这是非常之简洁啊，仅有主要的三个核心：topic(主题),brokerName(broker标识),queueId(队列id)。 

前面提到的客户端策略，会选择一个MessageQueue, 即会得到一个broker标识，对应一个queueId。所以，数据存放在哪个broker，是由客户端决定的，且存放位置未知。也就是说，rocketmq中同一个topic的数据，是散乱存放在一堆broker中的。这和我们通常的认知是有一定差距的。

这样设计有什么好处呢？好处自然是有的，比如假如其中有些broker挂掉了，那么整个集群无需经过什么再均衡策略，同样可以工作得很好，因为客户端可以直接向正常的broker发送消息即可。其他好处。。。

但是我个人觉得这样的设计，也不见得很好，比如你不能够很确定地定位到某条消息在哪个broker上，完全无规律可循。另外，如果想在单queueId上保持一定的规则，则是不可能的（也许有其他曲线救国之法）。另外，对于queueId, 只是一个系统内部的概念，实际上用户并不能指定该值。

5. MessageQueue到底存在哪里？

按照上面说的，一个topic数据可能被存放在n个broker中，且以messageQueue的queueId作为单独存储。那么，到底数据存放在哪里？所说的n个broker到底指哪几个broker？每个broker上到底存放了几个queueId？这些问题如果没有搞清楚，我们就无法说清楚这玩意。

我们先来回答第一个问题，topic数据到底存放在几个broker中？回顾下前面broker的注册过程可知：

// org.apache.rocketmq.namesrv.routeinfo.RouteInfoManager#registerBroker    if (null != topicConfigWrapper        && MixAll.MASTER_ID == brokerId) {        if (this.isBrokerTopicConfigChanged(brokerAddr, topicConfigWrapper.getDataVersion())            || registerFirst) {            // 首次注册或者topic变更，则更新topic信息            ConcurrentMap tcTable =                topicConfigWrapper.getTopicConfigTable();            if (tcTable != null) {                // 遍历所有topic, 将当前新进的broker 加入到处理机器中                for (Map.Entry entry : tcTable.entrySet()) {                    this.createAndUpdateQueueData(brokerName, entry.getValue());                }            }        }    }


看完这段，我们就明白了，原来所谓的n个broker可处理topic信息，实际上指的是所有broker啊！好吧，咱也不懂为啥这么干，反正就是这么干了，topic可能分布在所有broker机器上。至于具体哪一台，你猜啊！

接下来我们看第二个问题，一个broker到底存储了几个queueId的数据？实际上，我们稍微想想前面的实现，broker是指所有的broker，如果所有broker都是一样的配置，那么是不是应该让每个broker都存储所有queueId呢？（尽管没啥依据，还是可以想想的嘛）

rocketmq的各客户端（生产者、消费者）每次向服务器发送生产或消费请求时，都可能向nameserver请求拉取路由信息，但这些信息从我们前面调查的结果来看，并不包含queueId信息。那么，后续又是如何转换为queueId的呢？实际上，就是在拉取了nameserver的路由信息之后，本地再做一次分配就可以了：

// 更新topic路由信息    // org.apache.rocketmq.client.impl.producer.DefaultMQProducerImpl#tryToFindTopicPublishInfo    private TopicPublishInfo tryToFindTopicPublishInfo(final String topic) {        TopicPublishInfo topicPublishInfo = this.topicPublishInfoTable.get(topic);        if (null == topicPublishInfo || !topicPublishInfo.ok()) {            this.topicPublishInfoTable.putIfAbsent(topic, new TopicPublishInfo());            this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic);            topicPublishInfo = this.topicPublishInfoTable.get(topic);        }
        if (topicPublishInfo.isHaveTopicRouterInfo() || topicPublishInfo.ok()) {            return topicPublishInfo;        } else {            // 从nameserver拉取路由数据            this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);            topicPublishInfo = this.topicPublishInfoTable.get(topic);            return topicPublishInfo;        }    }    // org.apache.rocketmq.client.impl.factory.MQClientInstance#updateTopicRouteInfoFromNameServer    public boolean updateTopicRouteInfoFromNameServer(final String topic, boolean isDefault,        DefaultMQProducer defaultMQProducer) {        try {            if (this.lockNamesrv.tryLock(LOCK_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS)) {                try {                    TopicRouteData topicRouteData;                    if (isDefault && defaultMQProducer != null) {                        topicRouteData = this.mQClientAPIImpl.getDefaultTopicRouteInfoFromNameServer(defaultMQProducer.getCreateTopicKey(),                            1000 * 3);                        if (topicRouteData != null) {                            for (QueueData data : topicRouteData.getQueueDatas()) {                                int queueNums = Math.min(defaultMQProducer.getDefaultTopicQueueNums(), data.getReadQueueNums());                                data.setReadQueueNums(queueNums);                                data.setWriteQueueNums(queueNums);                            }                        }                    } else {                        topicRouteData = this.mQClientAPIImpl.getTopicRouteInfoFromNameServer(topic, 1000 * 3);                    }                    if (topicRouteData != null) {                        TopicRouteData old = this.topicRouteTable.get(topic);                        boolean changed = topicRouteDataIsChange(old, topicRouteData);                        if (!changed) {                            changed = this.isNeedUpdateTopicRouteInfo(topic);                        } else {                            log.info("the topic[{}] route info changed, old[{}] ,new[{}]", topic, old, topicRouteData);                        }
                        if (changed) {                            TopicRouteData cloneTopicRouteData = topicRouteData.cloneTopicRouteData();
                            for (BrokerData bd : topicRouteData.getBrokerDatas()) {                                this.brokerAddrTable.put(bd.getBrokerName(), bd.getBrokerAddrs());                            }
                            // Update Pub info                            {                                // 为每个broker分配queueId                                TopicPublishInfo publishInfo = topicRouteData2TopicPublishInfo(topic, topicRouteData);                                publishInfo.setHaveTopicRouterInfo(true);                                Iterator> it = this.producerTable.entrySet().iterator();                                while (it.hasNext()) {                                    Entry entry = it.next();                                    MQProducerInner impl = entry.getValue();                                    if (impl != null) {                                        impl.updateTopicPublishInfo(topic, publishInfo);                                    }                                }                            }
                            // Update sub info                            {                                Set subscribeInfo = topicRouteData2TopicSubscribeInfo(topic, topicRouteData);                                Iterator> it = this.consumerTable.entrySet().iterator();                                while (it.hasNext()) {                                    Entry entry = it.next();                                    MQConsumerInner impl = entry.getValue();                                    if (impl != null) {                                        impl.updateTopicSubscribeInfo(topic, subscribeInfo);                                    }                                }                            }                            log.info("topicRouteTable.put. Topic = {}, TopicRouteData[{}]", topic, cloneTopicRouteData);                            this.topicRouteTable.put(topic, cloneTopicRouteData);                            return true;                        }                    } else {                        log.warn("updateTopicRouteInfoFromNameServer, getTopicRouteInfoFromNameServer return null, Topic: {}", topic);                    }                } catch (MQClientException e) {                    if (!topic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {                        log.warn("updateTopicRouteInfoFromNameServer Exception", e);                    }                } catch (RemotingException e) {                    log.error("updateTopicRouteInfoFromNameServer Exception", e);                    throw new IllegalStateException(e);                } finally {                    this.lockNamesrv.unlock();                }            } else {                log.warn("updateTopicRouteInfoFromNameServer tryLock timeout {}ms", LOCK_TIMEOUT_MILLIS);            }        } catch (InterruptedException e) {            log.warn("updateTopicRouteInfoFromNameServer Exception", e);        }
        return false;    }

生产者分配queueId的实现如下：

// org.apache.rocketmq.client.impl.factory.MQClientInstance#topicRouteData2TopicPublishInfo    public static TopicPublishInfo topicRouteData2TopicPublishInfo(final String topic, final TopicRouteData route) {        TopicPublishInfo info = new TopicPublishInfo();        info.setTopicRouteData(route);        // 为每个broker指定queueId的分配情况（最大queueId）        // 这样的配置不知道累不累        if (route.getOrderTopicConf() != null && route.getOrderTopicConf().length() > 0) {            String[] brokers = route.getOrderTopicConf().split(";");            for (String broker : brokers) {                String[] item = broker.split(":");                int nums = Integer.parseInt(item[1]);                for (int i = 0; i < nums; i++) {                    MessageQueue mq = new MessageQueue(topic, item[0], i);                    info.getMessageQueueList().add(mq);                }            }
            info.setOrderTopic(true);        } else {            List qds = route.getQueueDatas();            Collections.sort(qds);            for (QueueData qd : qds) {                if (PermName.isWriteable(qd.getPerm())) {                    BrokerData brokerData = null;                    for (BrokerData bd : route.getBrokerDatas()) {                        if (bd.getBrokerName().equals(qd.getBrokerName())) {                            brokerData = bd;                            break;                        }                    }                    // 还是有broker无法处理queue哦                    if (null == brokerData) {                        continue;                    }                    // 非master节点不能接受写请求                    if (!brokerData.getBrokerAddrs().containsKey(MixAll.MASTER_ID)) {                        continue;                    }                    // 根据 writeQueueNums 数量，要求该broker接受所有小于该值的queueId                    for (int i = 0; i < qd.getWriteQueueNums(); i++) {                        MessageQueue mq = new MessageQueue(topic, qd.getBrokerName(), i);                        info.getMessageQueueList().add(mq);                    }                }            }
            info.setOrderTopic(false);        }
        return info;    }


可以看出，生产者对应的broker中，负责写的broker只能是master节点，负责所有小于writeQueueNums的queueId的数据存储。（如果所有broker配置一样，则相当于所有broker都存储所有queueId），所以，这存储关系，可能是理不清楚了。

我们再来看看消费者是如何对应queueId的呢？

// org.apache.rocketmq.client.impl.factory.MQClientInstance#topicRouteData2TopicSubscribeInfo    public static Set topicRouteData2TopicSubscribeInfo(final String topic, final TopicRouteData route) {        Set mqList = new HashSet();        List qds = route.getQueueDatas();        for (QueueData qd : qds) {            if (PermName.isReadable(qd.getPerm())) {                // 可读取broker上对应的所有小于readQueueNums 的队列                for (int i = 0; i < qd.getReadQueueNums(); i++) {                    MessageQueue mq = new MessageQueue(topic, qd.getBrokerName(), i);                    mqList.add(mq);                }            }        }
        return mqList;    }

原理和生产者差不多，就是通过一个 readQueueNums 来限定读取的队列数，基本上就是等于所有队列了，原因可能是原本数据就存储了所有queueId，如果消费者不读取，又该谁来读取呢。　

好了，到此我们总算厘清了整个rocketmq的消息存储定位方式了。总结一句话就是：任何节点都可能有任意topic的任意queueId数据。这结果，不禁又让我有一种千头万绪的感觉！

以上仅是一些正常的rocketmq数据存储的实现，只能算是皮毛。事实上，分布式系统中一个非常重要的能力是容错，欲知后事如何且听下回分解。


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出处：https://www.cnblogs.com/yougewe/p/14128845.html


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