关于源代码:通过源码分析RocketMQ主从复制原理

作者：京东物流宫丙来

一、主从复制概述

RocketMQ Broker的主从复制次要包含两局部内容：CommitLog的音讯复制和Broker元数据的复制。
CommitLog的音讯复制是产生在音讯写入时，当音讯写完Broker Master时，会通过独自的线程，将音讯写入到从服务器，在写入的时候反对同步写入、异步写入两种形式。
Broker元数据的写入，则是Broker从服务器通过独自的线程每隔10s从主Broker上获取，而后更新从的配置，并长久化到相应的配置文件中。
RocketMQ主从同步一个重要的特色：主从同步不具备主从切换性能，即当主节点宕机后，从不会接管音讯发送，但能够提供音讯读取。

二、CommitLog音讯复制

2.1、整体概述 CommitLog主从复制的流程如下：

1.Producer发送音讯到Broker Master，Broker进行音讯存储，并调用handleHA进行主从同步； 2.如果是同步复制的话，参考2.6章节的同步复制； 3.如果是异步复制的话，流程如下：

1. Broker Master启动，并在指定端口监听；
2. Broker Slave启动，被动连贯Broker Master，通过Java NIO建设TCP连贯；
3.  Broker Slave以每隔5s的间隔时间向服务端拉取音讯，如果是第一次拉取的话，先获取本地CommitLog文件中最大的偏移量，以该偏移量向服务端拉取音讯
4.  Broker Master 解析申请，并返回数据给Broker Slave；
5.Broker Slave收到一批音讯后，将音讯写入本地CommitLog文件中，而后向Master汇报拉取进度，并更新下一次待拉取偏移量；

咱们先看下异步复制的整体流程，最初再看下同步复制的流程，异步复制的入口为HAService.start();

public void start() throws Exception {
 //broker master启动，接管slave申请，并解决
    this.acceptSocketService.beginAccept();
    this.acceptSocketService.start();
 //同步复制线程启动
    this.groupTransferService.start();
 //broker slave启动
    this.haClient.start();
}

上面别离对下面的每一步做具体阐明。

2.2、HAService Master启动

public void beginAccept() throws Exception {
    this.serverSocketChannel = ServerSocketChannel.open();
    this.selector = RemotingUtil.openSelector();
    this.serverSocketChannel.socket().setReuseAddress(true);
    this.serverSocketChannel.socket().bind(this.socketAddressListen);
    this.serverSocketChannel.configureBlocking(false);
    this.serverSocketChannel.register(this.selector, SelectionKey.OP_ACCEPT);
}

在beginAccept办法中次要创立了ServerSocketChannel、Selector、设置TCP reuseAddress、绑定监听端口、设置为非阻塞模式，并注册OP_ACCEPT(连贯事件)。能够看到在这里是通过Java原生的NIO来实现的，并没有通过Netty框架来实现。

acceptSocketService.start()启动办法代码如下：

while (!this.isStopped()) {
    try {
   //获取事件
        this.selector.select(1000);
        Set<SelectionKey> selected = this.selector.selectedKeys();
        if (selected != null) {
            for (SelectionKey k : selected) {
//解决OP_ACCEPT事件，并创立HAConnection
                if ((k.readyOps() & SelectionKey.OP_ACCEPT) != 0) {
                    SocketChannel sc = ((ServerSocketChannel) k.channel()).accept();
                    if (sc != null) {
                       HAConnection conn = new HAConnection(HAService.this, sc);
                       //次要是启动readSocketService，writeSocketService这两个线程
 conn.start();
                       HAService.this.addConnection(conn);
                    }
                }
            }
            selected.clear();
        }
    } catch (Exception e) {
        log.error(this.getServiceName() + " service has exception.", e);
    }
}

选择器每1s解决一次解决一次连贯就绪事件。连贯事件就绪后，调用ServerSocketChannel的accept()办法创立SocketChannel，与服务端数据传输的通道。而后为每一个连贯创立一个HAConnection对象，该HAConnection将负责Master-Slave数据同步逻辑。HAConnection.start办法如下：

public void start() {
    this.readSocketService.start();
    this.writeSocketService.start();
}

2.3、HAClient启动

while (!this.isStopped()) {
    try {
        //和broker master建设连贯，通过java nio来实现
        if (this.connectMaster()) {
            //在心跳的同时，上报offset
            if (this.isTimeToReportOffset()) {
                //上报offset
                boolean result = this.reportSlaveMaxOffset(this.currentReportedOffset);
                if (!result) {
                    this.closeMaster();
                }
            }
            this.selector.select(1000);
            //解决网络读申请，也就是解决从Master传回的音讯数据
            boolean ok = this.processReadEvent();
            if (!ok) {
                this.closeMaster();
            }
            if (!reportSlaveMaxOffsetPlus()) {
                continue;
            }
            long interval =
                HAService.this.getDefaultMessageStore().getSystemClock().now()
                    - this.lastWriteTimestamp;
            if (interval > HAService.this.getDefaultMessageStore().getMessageStoreConfig()
                .getHaHousekeepingInterval()) {
                log.warn("HAClient, housekeeping, found this connection[" + this.masterAddress
                    + "] expired, " + interval);
                this.closeMaster();
                log.warn("HAClient, master not response some time, so close connection");
            }
        } else {
            this.waitForRunning(1000 * 5);
        }
    } catch (Exception e) {
        log.warn(this.getServiceName() + " service has exception. ", e);
        this.waitForRunning(1000 * 5);
    }
}

2.3.1、HAService主从建设连贯

如果socketChannel为空，则尝试连贯Master，如果Master地址为空，返回false。

private boolean connectMaster() throws ClosedChannelException {
    if (null == socketChannel) {
        String addr = this.masterAddress.get();
        if (addr != null) {
            SocketAddress socketAddress = RemotingUtil.string2SocketAddress(addr);
            if (socketAddress != null) {
                this.socketChannel = RemotingUtil.connect(socketAddress);
                if (this.socketChannel != null) {
                    //注册读事件，监听broker master返回的数据
                    this.socketChannel.register(this.selector, SelectionKey.OP_READ);
                }
            }
        }
        //获取以后的offset
        this.currentReportedOffset = HAService.this.defaultMessageStore.getMaxPhyOffset();
        this.lastWriteTimestamp = System.currentTimeMillis();
    }
    return this.socketChannel != null;
}

Broker 主从连贯

Broker Slave通过NIO来进行Broker Master连贯，代码如下：

SocketChannel sc = null;
sc = SocketChannel.open();
sc.configureBlocking(true);
sc.socket().setSoLinger(false, -1);
sc.socket().setTcpNoDelay(true);
sc.socket().setReceiveBufferSize(1024 * 64);
sc.socket().setSendBufferSize(1024 * 64);
sc.socket().connect(remote, timeoutMillis);
sc.configureBlocking(false);

Slave获取以后offset

public long getMaxPhyOffset() {
    return this.commitLog.getMaxOffset();
}
public long getMaxOffset() {
    return this.mappedFileQueue.getMaxOffset();
}
public long getMaxOffset() {
    MappedFile mappedFile = getLastMappedFile();
    if (mappedFile != null) {
        return mappedFile.getFileFromOffset() + mappedFile.getReadPosition();
    }
    return 0;
}

能够看到最终还是通过读取MappedFile的position来获取从的offset。

2.3.2、上报offset工夫判断

private boolean isTimeToReportOffset() {
    //以后工夫-上次写的工夫
    long interval =
        HAService.this.defaultMessageStore.getSystemClock().now() - this.lastWriteTimestamp;
    boolean needHeart = interval > HAService.this.defaultMessageStore.getMessageStoreConfig()
        .getHaSendHeartbeatInterval();


    return needHeart;
}

判断逻辑为以后工夫-上次写的工夫>haSendHeartbeatInterval时，则进行心跳和offset的上报。haSendHeartbeatInterval默认为5s，可配置。

2.3.3、上报offset

private boolean reportSlaveMaxOffset(final long maxOffset) {
    this.reportOffset.position(0);
    this.reportOffset.limit(8);
    this.reportOffset.putLong(maxOffset);
    this.reportOffset.position(0);
    this.reportOffset.limit(8);
    //最多发送三次，reportOffset是否有残余
    for (int i = 0; i < 3 && this.reportOffset.hasRemaining(); i++) {
        try {
            this.socketChannel.write(this.reportOffset);
        } catch (IOException e) {
            log.error(this.getServiceName()
                + "reportSlaveMaxOffset this.socketChannel.write exception", e);
            return false;
        }
    }
    return !this.reportOffset.hasRemaining();
}

次要还是通过NIO发送申请。

2.4、Broker Master解决申请

在主从建设连贯时创立了HAConnection对象，该对象次要蕴含了如下两个重要的线程服务类：

//负责写，将commitlog数据发送到从
private WriteSocketService writeSocketService;
//负责读，读取从上报的offset，并依据offset从Broker Master读取commitlog
private ReadSocketService readSocketService;

2.4.1、ReadSocketService接管读申请

readSocketService.run办法如下：

while (!this.isStopped()) {
    try {
        this.selector.select(1000);
        //解决读事件
        boolean ok = this.processReadEvent();
        if (!ok) {
            HAConnection.log.error("processReadEvent error");
            break;
        }
        long interval = HAConnection.this.haService.getDefaultMessageStore().getSystemClock().now() - this.lastReadTimestamp;
        if (interval > HAConnection.this.haService.getDefaultMessageStore().getMessageStoreConfig().getHaHousekeepingInterval()) {
            log.warn("ha housekeeping, found this connection[" + HAConnection.this.clientAddr + "] expired, " + interval);
            break;
        }
    } catch (Exception e) {
        HAConnection.log.error(this.getServiceName() + " service has exception.", e);
        break;
    }
}

processReadEvent的逻辑如下：

int readSize = this.socketChannel.read(this.byteBufferRead);
if (readSize > 0) {
    readSizeZeroTimes = 0;
    this.lastReadTimestamp = HAConnection.this.haService.getDefaultMessageStore().getSystemClock().now();
    if ((this.byteBufferRead.position() - this.processPostion) >= 8) {
        int pos = this.byteBufferRead.position() - (this.byteBufferRead.position() % 8);
        //获取slave 申请的offset
        long readOffset = this.byteBufferRead.getLong(pos - 8);
        this.processPostion = pos;


        HAConnection.this.slaveAckOffset = readOffset;
        if (HAConnection.this.slaveRequestOffset < 0) {
            HAConnection.this.slaveRequestOffset = readOffset;
            log.info("slave[" + HAConnection.this.clientAddr + "] request offset " + readOffset);
        }
        //如果是同步复制的话，判断申请的offset是否push2SlaveMaxOffset雷同，雷同的话则唤醒master GroupTransferService
        HAConnection.this.haService.notifyTransferSome(HAConnection.this.slaveAckOffset);
    }
}

能够看到processReadEvent逻辑很简略，就是从ByteBuffer中解析出offset，而后设置HAConnection.this.slaveRequestOffset；

2.4.2、WriteSocketService进行写解决

Broker Master通过HAConnection.WriteSocketService进行CommitLog的读取，run办法主逻辑如下：

this.selector.select(1000);
//nextTransferFromWhere下次传输commitLog的起始地位
if (-1 == this.nextTransferFromWhere) {
    if (0 == HAConnection.this.slaveRequestOffset) {
        long masterOffset = HAConnection.this.haService.getDefaultMessageStore().getCommitLog().getMaxOffset();
        masterOffset =
            masterOffset
                - (masterOffset % HAConnection.this.haService.getDefaultMessageStore().getMessageStoreConfig()
                .getMapedFileSizeCommitLog());


        if (masterOffset < 0) {
            masterOffset = 0;
        }


        this.nextTransferFromWhere = masterOffset;
    } else {
        this.nextTransferFromWhere = HAConnection.this.slaveRequestOffset;
    }


    log.info("master transfer data from " + this.nextTransferFromWhere + " to slave[" + HAConnection.this.clientAddr
        + "], and slave request " + HAConnection.this.slaveRequestOffset);
}


//获取commitLog数据
SelectMappedBufferResult selectResult = HAConnection.this.haService.getDefaultMessageStore().getCommitLogData(this.nextTransferFromWhere);
//获取commitLog数据
SelectMappedBufferResult selectResult =
    HAConnection.this.haService.getDefaultMessageStore().getCommitLogData(this.nextTransferFromWhere);
if (selectResult != null) {
    int size = selectResult.getSize();
    if (size > HAConnection.this.haService.getDefaultMessageStore().getMessageStoreConfig().getHaTransferBatchSize()) {
        size = HAConnection.this.haService.getDefaultMessageStore().getMessageStoreConfig().getHaTransferBatchSize();
    }


    long thisOffset = this.nextTransferFromWhere;
    this.nextTransferFromWhere += size;


    selectResult.getByteBuffer().limit(size);
    this.selectMappedBufferResult = selectResult;


    // Build Header
    this.byteBufferHeader.position(0);
    this.byteBufferHeader.limit(headerSize);
    this.byteBufferHeader.putLong(thisOffset);
    this.byteBufferHeader.putInt(size);
    this.byteBufferHeader.flip();
    //nio发送commitlog
    this.lastWriteOver = this.transferData();
} else {
    //如果没有获取到commitLog数据，期待100ms
    HAConnection.this.haService.getWaitNotifyObject().allWaitForRunning(1

这外面次要包含获取CommitLog数据、发送CommitLog数据这两个步骤。

2.4.2.1、获取CommitLog数据

public SelectMappedBufferResult getData(final long offset, final boolean returnFirstOnNotFound) {
    int mappedFileSize = this.defaultMessageStore.getMessageStoreConfig().getMapedFileSizeCommitLog();
    MappedFile mappedFile = this.mappedFileQueue.findMappedFileByOffset(offset, returnFirstOnNotFound);
    if (mappedFile != null) {
        int pos = (int) (offset % mappedFileSize);
        SelectMappedBufferResult result = mappedFile.selectMappedBuffer(pos);
        return result;
    }
    return null;
}
public SelectMappedBufferResult selectMappedBuffer(int pos) {
    int readPosition = getReadPosition();
    if (pos < readPosition && pos >= 0) {
        if (this.hold()) {
            ByteBuffer byteBuffer = this.mappedByteBuffer.slice();
            byteBuffer.position(pos);
            int size = readPosition - pos;
            ByteBuffer byteBufferNew = byteBuffer.slice();
            byteBufferNew.limit(size);
            return new SelectMappedBufferResult(this.fileFromOffset + pos, byteBufferNew, size, this);
        }
    }
    return null;
}

能够看到最终还是依据offset从MappedFile读取数据。

2.4.2.2、发送CommitLog数据

数据次要包含header、body两局部，数据发送的话还是通过NIO来实现，次要代码如下：

// Build Header
this.byteBufferHeader.position(0);
this.byteBufferHeader.limit(headerSize);
this.byteBufferHeader.putLong(thisOffset);
this.byteBufferHeader.putInt(size);
this.byteBufferHeader.flip();


int writeSize = this.socketChannel.write(this.byteBufferHeader);
// Write Body
if (!this.byteBufferHeader.hasRemaining()) {
    while (this.selectMappedBufferResult.getByteBuffer().hasRemaining()) {
        int writeSize = this.socketChannel.write(this.selectMappedBufferResult.getByteBuffer());
        if (writeSize > 0) {
            writeSizeZeroTimes = 0;
            this.lastWriteTimestamp = HAConnection.this.haService.getDefaultMessageStore().getSystemClock().now();
        } else if (writeSize == 0) {
            if (++writeSizeZeroTimes >= 3) {
                break;
            }
        } else {
            throw new Exception("ha master write body error < 0");
        }
    }
}

CommitLog主从发送实现后，Broker Slave则会监听读事件、获取CommitLog数据，并进行CommitLog的写入。

2.5、HAClient processReadEvent

在主从建设连贯后，从注册了可读事件，目标就是读取从Broker Master返回的CommitLog数据，对应的办法为HAClient.processReadEvent：

int readSize = this.socketChannel.read(this.byteBufferRead);
if (readSize > 0) {
    lastWriteTimestamp = HAService.this.defaultMessageStore.getSystemClock().now();
    readSizeZeroTimes = 0;
    boolean result = this.dispatchReadRequest();
    if (!result) {
        log.error("HAClient, dispatchReadRequest error");
        return false;
    }
}

dispatchReadRequest办法如下：

 //读取返回的body data
byte[] bodyData = new byte[bodySize];
this.byteBufferRead.position(this.dispatchPostion + msgHeaderSize);
this.byteBufferRead.get(bodyData);


HAService.this.defaultMessageStore.appendToCommitLog(masterPhyOffset, bodyData);


this.byteBufferRead.position(readSocketPos);
this.dispatchPostion += msgHeaderSize + bodySize;


//上报从的offset
if (!reportSlaveMaxOffsetPlus()) {
    return false;

外面的外围逻辑次要包含如下三个步骤：

从byteBufferRead中读取CommitLog数据；

<!—->

调用defaultMessageStore.appendToCommitLog办法，将数据写入到MappedFile文件，写入办法如下：

public boolean appendToCommitLog(long startOffset, byte[] data) {
    //将数据写到commitlog，同一般音讯的存储
    boolean result = this.commitLog.appendData(startOffset, data);
    //唤醒reputMessageService，构建consumeQueue,index
    this.reputMessageService.wakeup();
    return result;
}

上报从新的offset，也是读取MappedFile的offset，而后上报Broker Master；

2.6、同步复制

下面次要介绍了Broker的异步复制，上面再来看下Broker的同步复制的实现。同步复制的整体流程图如下：

大略阐明如下：

producer发送音讯到broker，broker进行音讯的存储，将音讯写入到commitLog；
broker master写音讯线程唤醒WriteSocketService线程，查问commitLog数据，而后发送到从。在WriteSocketService获取commitLog时，如果没有获取到commitLog数据，会期待100ms。所以当commitLog新写入数据的时候，会唤醒WriteSocketService，而后查问commitLog数据，发送到从。
broker master创立GroupCommitRequest，同步期待主从复制实现；
从承受新的commitLog数据，而后写commitLog数据，并返回新的slave offset到主；
主更新push2SlaveMaxOffset，并判断push2SlaveMaxOffset是否大于等于主从复制申请的offset，如果大于等于的话，则认为主从复制实现，返回commitLog.handleHA办法胜利，从而返回音讯保留胜利。

对应的代码入口为CommitLog.handleHA办法。

public void handleHA(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) {
    //如果是broker主，并且是同步复制的话
    if (BrokerRole.SYNC_MASTER == this.defaultMessageStore.getMessageStoreConfig().getBrokerRole()) {
        //获取HAService
        HAService service = this.defaultMessageStore.getHaService();
        //获取Message上的MessageConst.PROPERTY_WAIT_STORE_MSG_OK，默认是须要期待主从复制实现
        if (messageExt.isWaitStoreMsgOK()) {
            /**
             * 判断从是否可用，判断的逻辑是：（主offset-push2SlaveMaxOffset<1024 * 1024 * 256），也就是如果主从的offset差的太多，
             * 则认为从不可用， Tell the producer, slave not available
             * 这里的result = mappedFile.appendMessage(msg, this.appendMessageCallback);
             */
            if (service.isSlaveOK(result.getWroteOffset() + result.getWroteBytes())) {
                //组装GroupCommitRequest，nextOffset=result.getWroteOffset() + result.getWroteBytes()，这里的nextOffset指的就是从要写到的offset
                GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());
                                    /**
                * 调用的是this.groupTransferService.putRequest(request);将request放到requestsWrite list中。
                  * HAService持有GroupTransferService groupTransferService援用;
                */
                service.putRequest(request);
                 /**
                     * 唤醒的是WriteSocketService，查问commitLog数据，而后发送到从。
                     * 在WriteSocketService获取commitLog时，如果没有获取到commitLog数据，期待100ms
                     * HAConnection.this.haService.getWaitNotifyObject().allWaitForRunning(100);
                     * 所以当commitLog新写入数据的时候，会唤醒WriteSocketService，而后查问commitLog数据，发送到从。
                     */
                service.getWaitNotifyObject().wakeupAll();


                //期待同步复制实现，判断逻辑是： HAService.this.push2SlaveMaxOffset.get() >= req.getNextOffset();
                boolean flushOK =
                    request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());


                //如果同步复制失败的话，设置putMessageResult中的状态为同步从超时
                if (!flushOK) {
                    log.error("do sync transfer other node, wait return, but failed, topic: " + messageExt.getTopic() + " tags: "
                        + messageExt.getTags() + " client address: " + messageExt.getBornHostNameString());
                    putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_SLAVE_TIMEOUT);
                }
            }
            // Slave problem
            else {
                // Tell the producer, slave not available
                putMessageResult.setPutMessageStatus(PutMessageStatus.SLAVE_NOT_AVAILABLE);
            }
        }
    }

2.6.1、GroupTransferService启动

在HAService启动的时候，启动了GroupTransferService线程，代码如下：

public void run() {
    while (!this.isStopped()) {
        this.waitForRunning(10);
        this.doWaitTransfer();
    }
}
private void doWaitTransfer() {
    synchronized (this.requestsRead) {
        if (!this.requestsRead.isEmpty()) {
            for (CommitLog.GroupCommitRequest req : this.requestsRead) {
                /**
                 * req.getNextOffset：result.getWroteOffset() + result.getWroteBytes()
                 * push2SlaveMaxOffset：
                 */
                boolean transferOK = HAService.this.push2SlaveMaxOffset.get() >= req.getNextOffset();
                //在这循环5次，最多期待5s，因为slave 心跳距离默认5s
                for (int i = 0; !transferOK && i < 5; i++) {
                    this.notifyTransferObject.waitForRunning(1000);
                    transferOK = HAService.this.push2SlaveMaxOffset.get() >= req.getNextOffset();
                }
                if (!transferOK) {
                    log.warn("transfer messsage to slave timeout, " + req.getNextOffset());
                }
                //主从复制实现，唤醒handleHA后续操作
                req.wakeupCustomer(transferOK);
            }
            this.requestsRead.clear();
        }
    }
}

wakeupCustomer：

public void wakeupCustomer(final boolean flushOK) {
    this.flushOK = flushOK;
    this.countDownLatch.countDown();
}

2.6.2、唤醒WriteSocketService

service.getWaitNotifyObject().wakeupAll();

唤醒的是WriteSocketService，查问commitLog数据，而后发送到从。在WriteSocketService获取commitLog时，如果没有获取到commitLog数据，期待100ms。HAConnection.this.haService.getWaitNotifyObject().allWaitForRunning(100);所以当commitLog新写入数据的时候，会唤醒WriteSocketService，而后查问commitLog数据，发送到从。

2.6.3、同步期待，直到复制实现

boolean flushOK =
    request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());


public boolean waitForFlush(long timeout) {
    try {
        //期待同步复制实现
        this.countDownLatch.await(timeout, TimeUnit.MILLISECONDS);
        return this.flushOK;
    } catch (InterruptedException e) {
        log.error("Interrupted", e);
        return false;
    }
}
}

三、元数据的复制

broker元数据的复制，次要包含topicConfig、consumerOffset、delayOffset、subscriptionGroup这几局部，整体流程图如下：

从broker通过独自的线程，每隔10s进行一次元数据的复制，代码入口为：BrokerController.start -> SlaveSynchronize.syncAll：

slaveSyncFuture = this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
    @Override
    public void run() {
        try {
            //10s 进行一次主从同步
            BrokerController.this.slaveSynchronize.syncAll();
        }
        catch (Throwable e) {
            log.error("ScheduledTask SlaveSynchronize syncAll error.", e);
        }
    }
}, 1000 * 3, 1000 * 10, TimeUnit.MILLISECONDS);


public void syncAll() {
    this.syncTopicConfig();
    this.syncConsumerOffset();
    this.syncDelayOffset();
    this.syncSubscriptionGroupConfig();
}

3.1、syncTopicConfig

//从Master获取TopicConfig信息，最终调用的是AdminBrokerProcessor.getAllTopicConfig
TopicConfigSerializeWrapper topicWrapper =
    this.brokerController.getBrokerOuterAPI().getAllTopicConfig(masterAddrBak);
if (!this.brokerController.getTopicConfigManager().getDataVersion()
    .equals(topicWrapper.getDataVersion())) {
    this.brokerController.getTopicConfigManager().getDataVersion()
        .assignNewOne(topicWrapper.getDataVersion());
    this.brokerController.getTopicConfigManager().getTopicConfigTable().clear();
    this.brokerController.getTopicConfigManager().getTopicConfigTable()
        .putAll(topicWrapper.getTopicConfigTable());
 //将topicConfig进行长久化，对应的文件为topics.json
    this.brokerController.getTopicConfigManager().persist();
    log.info("Update slave topic config from master, {}", masterAddrBak)

3.2、syncConsumerOffset

//从"主Broker"获取ConsumerOffset
ConsumerOffsetSerializeWrapper offsetWrapper =
        this.brokerController.getBrokerOuterAPI().getAllConsumerOffset(masterAddrBak);
//设置从的offsetTable
this.brokerController.getConsumerOffsetManager().getOffsetTable()
                    .putAll(offsetWrapper.getOffsetTable());
//并长久化到从的consumerOffset.json文件中
this.brokerController.getConsumerOffsetManager().persist();

3.3、syncDelayOffset

String delayOffset = this.brokerController.getBrokerOuterAPI().getAllDelayOffset(masterAddrBak);
String fileName = StorePathConfigHelper.getDelayOffsetStorePath(this.brokerController
.getMessageStoreConfig().getStorePathRootDir());
 MixAll.string2File(delayOffset, fileName);

3.4、syncSubscriptionGroupConfig

SubscriptionGroupWrapper subscriptionWrapper =this.brokerController.getBrokerOuterAPI().getAllSubscriptionGroupConfig(masterAddrBak);
SubscriptionGroupManager subscriptionGroupManager =this.brokerController.getSubscriptionGroupManager();
subscriptionGroupManager.getDataVersion().assignNewOne(subscriptionWrapper.getDataVersion());
subscriptionGroupManager.getSubscriptionGroupTable().clear();
subscriptionGroupManager.getSubscriptionGroupTable().putAll(subscriptionWrapper.getSubscriptionGroupTable());
subscriptionGroupManager.persist();

四、思考与播种

通过下面的分享，咱们基本上理解了RocketMQ的主从复制原理，其中有些思维咱们能够后续借鉴下：

在功能设计的时候将元数据、程序数据离开治理；
主从复制的时候，根本思维都是从申请主，申请时带上offset，而后主查问数据返回从，从再执行；mysql的主从复制、redis的主从复制根本也是这样；
主从复制包含异步复制、同步复制两种形式，能够通过配置来决定应用哪种同步形式，这个须要依据理论业务场景来决定；
主从复制线程尽量和音讯写线程或者主线程离开；

因为工夫、精力有限，难免会有纰漏、思考不到之处，如有问题欢送沟通、交换。

关于源代码:通过源码分析RocketMQ主从复制原理

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关于源代码:通过源码分析RocketMQ主从复制原理

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