作者：京東物流 宮丙來
一、主從復制概述
- RocketMQ Broker的主從復制主要包括兩部分內容：CommitLog的消息復制和Broker元數據的復制。
- CommitLog的消息復制是發生在消息寫入時，當消息寫完Broker Master時，會通過單獨的線程，將消息寫入到從服務器，在寫入的時候支持同步寫入、異步寫入兩種方式。
- Broker元數據的寫入，則是Broker從服務器通過單獨的線程每隔10s從主Broker上獲取，然后更新從的配置，并持久化到相應的配置文件中。
- RocketMQ主從同步一個重要的特征：主從同步不具備主從切換功能，即當主節點宕機后，從不會接管消息發送，但可以提供消息讀取。
二、CommitLog消息復制
2.1、整體概述
CommitLog主從復制的流程如下：
1.Producer發送消息到Broker Master，Broker進行消息存儲，并調用handleHA進行主從同步； 2.如果是同步復制的話，參考2.6章節的同步復制； 3.如果是異步復制的話，流程如下：
1. Broker Master啟動，并在指定端口監聽；
2. Broker Slave啟動，主動連接Broker Master，通過JAVA NIO建立TCP連接；
3. Broker Slave以每隔5s的間隔時間向服務端拉取消息，如果是第一次拉取的話，先獲取本地CommitLog文件中最大的偏移量，以該偏移量向服務端拉取消息
4. Broker Master 解析請求，并返回數據給Broker Slave；
5.Broker Slave收到一批消息后，將消息寫入本地CommitLog文件中，然后向Master匯報拉取進度，并更新下一次待拉取偏移量；
我們先看下異步復制的整體流程，最后再看下同步復制的流程，異步復制的入口為HAService.start();
public void start() throws Exception {
//broker master啟動，接收slave請求，并處理
this.acceptSocketService.beginAccept();
this.acceptSocketService.start();
//同步復制線程啟動
this.groupTransferService.start();
//broker slave啟動
this.haClient.start();
}
下面分別對上面的每一步做詳細說明。
2.2、HAService Master啟動
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方法中主要創建了ServerSocketChannel、Selector、設置TCP reuseAddress、綁定監聽端口、設置為非阻塞模式，并注冊OP_ACCEPT(連接事件)。可以看到在這里是通過Java原生的NIO來實現的，并沒有通?.NETty框架來實現。
acceptSocketService.start()啟動方法代碼如下：
while (!this.isStopped()) {
try {
//獲取事件
this.selector.select(1000);
Set<SelectionKey> selected = this.selector.selectedKeys();
if (selected != null) {
for (SelectionKey k : selected) {
//處理OP_ACCEPT事件，并創建HAConnection
if ((k.readyOps() & SelectionKey.OP_ACCEPT) != 0) {
SocketChannel sc = ((ServerSocketChannel) k.channel()).accept();
if (sc != null) {
HAConnection conn = new HAConnection(HAService.this, sc);
//主要是啟動readSocketService，writeSocketService這兩個線程
conn.start();
HAService.this.addConnection(conn);
}
}
}
selected.clear();
}
} catch (Exception e) {
log.error(this.getServiceName() + " service has exception.", e);
}
}
選擇器每1s處理一次處理一次連接就緒事件。連接事件就緒后，調用ServerSocketChannel的accept()方法創建SocketChannel，與服務端數據傳輸的通道。然后為每一個連接創建一個HAConnection對象，該HAConnection將負責Master-Slave數據同步邏輯。HAConnection.start方法如下：
public void start() {
this.readSocketService.start();
this.writeSocketService.start();
}
2.3、HAClient啟動
while (!this.isStopped()) {
try {
//和broker master建立連接，通過java nio來實現
if (this.connectMaster()) {
//在心跳的同時，上報offset
if (this.isTimeToReportOffset()) {
//上報offset
boolean result = this.reportSlaveMaxOffset(this.currentReportedOffset);
if (!result) {
this.closeMaster();
}
}
this.selector.select(1000);
//處理網絡讀請求，也就是處理從Master傳回的消息數據
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主從建立連接
如果socketChannel為空，則嘗試連接Master，如果Master地址為空，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) {
//注冊讀事件，監聽broker master返回的數據
this.socketChannel.register(this.selector, SelectionKey.OP_READ);
}
}
}
//獲取當前的offset
this.currentReportedOffset = HAService.this.defaultMessageStore.getMaxPhyOffset();
this.lastWriteTimestamp = System.currentTimeMillis();
}
return this.socketChannel != null;
}
- Broker 主從連接
Broker Slave通過NIO來進行Broker Master連接，代碼如下：
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獲取當前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;
}
可以看到最終還是通過讀取MappedFile的position來獲取從的offset。
2.3.2、上報offset時間判斷
private boolean isTimeToReportOffset() {
//當前時間-上次寫的時間
long interval =
HAService.this.defaultMessageStore.getSystemClock().now() - this.lastWriteTimestamp;
boolean needHeart = interval > HAService.this.defaultMessageStore.getMessageStoreConfig()
.getHaSendHeartbeatInterval();
return needHeart;
}
判斷邏輯為當前時間-上次寫的時間>haSendHeartbeatInterval時，則進行心跳和offset的上報。haSendHeartbeatInterval默認為5s，可配置。
2.3.3、上報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);
//最多發送三次，reportOffset是否有剩余
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();
}
主要還是通過NIO發送請求。
2.4、Broker Master處理請求
在主從建立連接時創建了HAConnection對象，該對象主要包含了如下兩個重要的線程服務類：
//負責寫，將commitlog數據發送到從
private WriteSocketService writeSocketService;
//負責讀，讀取從上報的offset，并根據offset從Broker Master讀取commitlog
private ReadSocketService readSocketService;
2.4.1、ReadSocketService接收讀請求
readSocketService.run方法如下：
while (!this.isStopped()) {
try {
this.selector.select(1000);
//處理讀事件
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的邏輯如下：
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);
//獲取slave 請求的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);
}
//如果是同步復制的話，判斷請求的offset是否push2SlaveMaxOffset相同，相同的話則喚醒master GroupTransferService
HAConnection.this.haService.notifyTransferSome(HAConnection.this.slaveAckOffset);
}
}
可以看到processReadEvent邏輯很簡單，就是從ByteBuffer中解析出offset，然后設置
HAConnection.this.slaveRequestOffset；
2.4.2、WriteSocketService進行寫處理
Broker Master通過
HAConnection.WriteSocketService進行CommitLog的讀取，run方法主邏輯如下：
this.selector.select(1000);
//nextTransferFromWhere下次傳輸commitLog的起始位置
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);
}
//獲取commitLog數據
SelectMappedBufferResult selectResult = HAConnection.this.haService.getDefaultMessageStore().getCommitLogData(this.nextTransferFromWhere);
//獲取commitLog數據
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發送commitlog
this.lastWriteOver = this.transferData();
} else {
//如果沒有獲取到commitLog數據，等待100ms
HAConnection.this.haService.getWaitNotifyObject().allWaitForRunning(1
這里面主要包括獲取CommitLog數據、發送CommitLog數據這兩個步驟。
2.4.2.1、獲取CommitLog數據
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;
}
可以看到最終還是根據offset從MappedFile讀取數據。
2.4.2.2、發送CommitLog數據
數據主要包括header、body兩部分，數據發送的話還是通過NIO來實現，主要代碼如下：
// 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主從發送完成后，Broker Slave則會監聽讀事件、獲取CommitLog數據，并進行CommitLog的寫入。
2.5、HAClient processReadEvent
在主從建立連接后，從注冊了可讀事件，目的就是讀取從Broker Master返回的CommitLog數據，對應的方法為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方法如下：
//讀取返回的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;
//上報從的offset
if (!reportSlaveMaxOffsetPlus()) {
return false;
里面的核心邏輯主要包括如下三個步驟：
- 從byteBufferRead中讀取CommitLog數據；
- 調用defaultMessageStore.appendToCommitLog方法，將數據寫入到MappedFile文件，寫入方法如下：
public boolean appendToCommitLog(long startOffset, byte[] data) {
//將數據寫到commitlog，同普通消息的存儲
boolean result = this.commitLog.appendData(startOffset, data);
//喚醒reputMessageService，構建consumeQueue,index
this.reputMessageService.wakeup();
return result;
}
- 上報從新的offset，也是讀取MappedFile的offset，然后上報Broker Master；
2.6、同步復制
上面主要介紹了Broker的異步復制，下面再來看下Broker的同步復制的實現。同步復制的整體流程圖如下：
大概說明如下：
- producer發送消息到broker，broker進行消息的存儲，將消息寫入到commitLog；
- broker master寫消息線程喚醒WriteSocketService線程，查詢commitLog數據，然后發送到從。在WriteSocketService獲取commitLog時，如果沒有獲取到commitLog數據，會等待100ms。所以當commitLog新寫入數據的時候，會喚醒WriteSocketService，然后查詢commitLog數據，發送到從。
- broker master創建GroupCommitRequest，同步等待主從復制完成；
- 從接受新的commitLog數據，然后寫commitLog數據，并返回新的slave offset到主；
- 主更新push2SlaveMaxOffset，并判斷push2SlaveMaxOffset是否大于等于主從復制請求的offset，如果大于等于的話，則認為主從復制完成，返回commitLog.handleHA方法成功，從而返回消息保存成功。
對應的代碼入口為CommitLog.handleHA方法。
public void handleHA(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) {
//如果是broker主，并且是同步復制的話
if (BrokerRole.SYNC_MASTER == this.defaultMessageStore.getMessageStoreConfig().getBrokerRole()) {
//獲取HAService
HAService service = this.defaultMessageStore.getHaService();
//獲取Message上的MessageConst.PROPERTY_WAIT_STORE_MSG_OK，默認是需要等待主從復制完成
if (messageExt.isWaitStoreMsgOK()) {
/**
* 判斷從是否可用，判斷的邏輯是：（主offset-push2SlaveMaxOffset<1024 * 1024 * 256），也就是如果主從的offset差的太多，
* 則認為從不可用， Tell the producer, slave not available
* 這里的result = mappedFile.appendMessage(msg, this.appendMessageCallback);
*/
if (service.isSlaveOK(result.getWroteOffset() + result.getWroteBytes())) {
//組裝GroupCommitRequest，nextOffset=result.getWroteOffset() + result.getWroteBytes()，這里的nextOffset指的就是從要寫到的offset
GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());
/**
* 調用的是this.groupTransferService.putRequest(request);將request放到requestsWrite list中。
* HAService持有GroupTransferService groupTransferService引用;
*/
service.putRequest(request);
/**
* 喚醒的是WriteSocketService，查詢commitLog數據，然后發送到從。
* 在WriteSocketService獲取commitLog時，如果沒有獲取到commitLog數據，等待100ms
* HAConnection.this.haService.getWaitNotifyObject().allWaitForRunning(100);
* 所以當commitLog新寫入數據的時候，會喚醒WriteSocketService，然后查詢commitLog數據，發送到從。
*/
service.getWaitNotifyObject().wakeupAll();
//等待同步復制完成，判斷邏輯是： HAService.this.push2SlaveMaxOffset.get() >= req.getNextOffset();
boolean flushOK =
request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
//如果同步復制失敗的話，設置putMessageResult中的狀態為同步從超時
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啟動
在HAService啟動的時候，啟動了GroupTransferService線程，代碼如下：
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();
//在這循環5次，最多等待5s，因為slave 心跳間隔默認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());
}
//主從復制完成，喚醒handleHA后續操作
req.wakeupCustomer(transferOK);
}
this.requestsRead.clear();
}
}
}
wakeupCustomer：
public void wakeupCustomer(final boolean flushOK) {
this.flushOK = flushOK;
this.countDownLatch.countDown();
}
2.6.2、喚醒WriteSocketService
service.getWaitNotifyObject().wakeupAll();
喚醒的是WriteSocketService，查詢commitLog數據，然后發送到從。在WriteSocketService獲取commitLog時，如果沒有獲取到commitLog數據，等待100ms。
HAConnection.this.haService.getWaitNotifyObject().allWaitForRunning(100);所以當commitLog新寫入數據的時候，會喚醒WriteSocketService，然后查詢commitLog數據，發送到從。
2.6.3、同步等待，直到復制完成
boolean flushOK =
request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
public boolean waitForFlush(long timeout) {
try {
//等待同步復制完成
this.countDownLatch.await(timeout, TimeUnit.MILLISECONDS);
return this.flushOK;
} catch (InterruptedException e) {
log.error("Interrupted", e);
return false;
}
}
}
三、元數據的復制
broker元數據的復制，主要包括topicConfig、consumerOffset、delayOffset、subscriptionGroup這幾部分，整體流程圖如下：
從broker通過單獨的線程，每隔10s進行一次元數據的復制 ，代碼入口為：BrokerController.start -> SlaveSynchronize.syncAll：
slaveSyncFuture = this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
try {
//10s 進行一次主從同步
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
//從Master獲取TopicConfig信息，最終調用的是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());
//將topicConfig進行持久化，對應的文件為topics.json
this.brokerController.getTopicConfigManager().persist();
log.info("Update slave topic config from master, {}", masterAddrBak)
3.2、syncConsumerOffset
//從"主Broker"獲取ConsumerOffset
ConsumerOffsetSerializeWrapper offsetWrapper =
this.brokerController.getBrokerOuterAPI().getAllConsumerOffset(masterAddrBak);
//設置從的offsetTable
this.brokerController.getConsumerOffsetManager().getOffsetTable()
.putAll(offsetWrapper.getOffsetTable());
//并持久化到從的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、思考與收獲
通過上面的分享，我們基本上了解了RocketMQ的主從復制原理，其中有些思想我們可以后續借鑒下：
- 在功能設計的時候將元數據、程序數據分開管理；
- 主從復制的時候，基本思想都是從請求主，請求時帶上offset，然后主查詢數據返回從，從再執行；MySQL的主從復制、redis的主從復制基本也是這樣；
- 主從復制包括異步復制、同步復制兩種方式，可以通過配置來決定使用哪種同步方式，這個需要根據實際業務場景來決定；
- 主從復制線程盡量和消息寫線程或者主線程分開；
由于時間、精力有限，難免會有紕漏、考慮不到之處，如有問題歡迎溝通、交流。
