目錄

一、消息存儲概覽

二、Broker接收消息

三、消息存儲流程

1.?DefaultMessageStore類

2. 存儲流程

????????1)：同步與異步存儲

????????2)：CommitLog異步存儲消息

????????3)：提交消息（Commit）

四、參考資料

---

一、消息存儲概覽

????????如下圖所示，是消息從生產(chǎn)者發(fā)送消息到消費(fèi)者消費(fèi)消息的大致流程。

• step1：生產(chǎn)者發(fā)送消息到消息存儲Broker端；
• step2：單一文件Commitlog存儲所有主題消息，確保順序?qū)懭?#xff0c;提高吞吐量；
• step3：消息通過堆外緩存，Commit消息寫入文件內(nèi)存映射，然后Flush寫入磁盤；
• step4：消息Flush磁盤后，把消息轉(zhuǎn)發(fā)到ConsumeQueue、IndexFile供消費(fèi)者消費(fèi)；
• step5：主題下消費(fèi)隊(duì)列內(nèi)容相同，但是一個消費(fèi)隊(duì)列在同一時刻只能被一個消費(fèi)者消費(fèi)；
• step6：消費(fèi)者根據(jù)集群/廣播模式、PUSH/PULL模式來消費(fèi)消息。

????????如何實(shí)現(xiàn)順序存儲的呢？通過org.apache.rocketmq.store.PutMessageLock接口，在消息追加文件內(nèi)存映射時，加鎖實(shí)現(xiàn)存儲消息串行。

? ? ? ? 消息存儲模式：同步、異步。默認(rèn)異步存儲，但是無論同步還是異步，最終執(zhí)行存儲方法是org.apache.rocketmq.store.CommitLog#asyncPutMessage（異步執(zhí)行，提高存儲效率），而同步需要等待存儲結(jié)果才能返回。

? ? ? ? 本章主要介紹生產(chǎn)者發(fā)送消息，Broker如何接收消息，如何Commit寫入文件內(nèi)存映射，并沒有介紹如何刷盤、轉(zhuǎn)發(fā)到ConsumeQueue和IndexFile、HA主從同步等內(nèi)容。

二、Broker接收消息

????????org.apache.rocketmq.broker.processor.SendMessageProcessor是生產(chǎn)者發(fā)送消息后，Broker接收消息的核心實(shí)現(xiàn)類。 發(fā)送消息請求碼是RequestCode.SEND_MESSAGE。發(fā)送消息參考《RocketMQ5.0.0消息發(fā)送》。

????????org.apache.rocketmq.broker.processor.SendMessageProcessor#processRequest不僅處理生產(chǎn)者發(fā)來的消息，同時還是處理消費(fèi)端消費(fèi)ACK的處理請求。其核心邏輯是sendMessage或sendBatchMessage處理方法，都是Broker端存儲消息。

????????以下代碼是org.apache.rocketmq.broker.processor.SendMessageProcessor#sendMessage存儲之前對消息的預(yù)處理。 核心邏輯如下：

• randomQueueId()：發(fā)送時是否指定消費(fèi)隊(duì)列，若沒有指定，則隨機(jī)選擇；
• handleRetryAndDLQ()：消息是否延遲或重試消息，并處理；
• sendTransactionPrepareMessage變量：判定是否事務(wù)消息，true事務(wù)消息；
• 異步存儲消息（默認(rèn)）：

????????????????事務(wù)消息存儲：TransactionalMessageServiceImpl#asyncPrepareMessage

? ? ? ? ? ? ? ? 普通消息存儲：DefaultMessageStore#asyncPutMessage

• 同步存儲消息：

????????????????事務(wù)消息存儲：TransactionalMessageServiceImpl#prepareMessage

????????????????普通消息存儲：DefaultMessageStore#putMessage

/*** 存儲之前，對消息的處理* step1：預(yù)發(fā)送處理，如：檢查消息、主題是否符合規(guī)范* step2：發(fā)送消息時，是否指定消費(fèi)隊(duì)列，若沒有則隨機(jī)選擇* step3：消息是否進(jìn)入重試或延遲隊(duì)列中（重試次數(shù)失敗）* step4：消息是否是事務(wù)消息，若是則存儲為prepare消息* step5：BrokerConfig#asyncSendEnable是否開啟異步存儲，默認(rèn)開啟true*        (異步存儲、同步存儲)*/
public RemotingCommand sendMessage(final ChannelHandlerContext ctx,final RemotingCommand request,final SendMessageContext sendMessageContext,final SendMessageRequestHeader requestHeader,final TopicQueueMappingContext mappingContext,final SendMessageCallback sendMessageCallback) throws RemotingCommandException {// 預(yù)發(fā)送處理，如：檢查消息、主題是否符合規(guī)范final RemotingCommand response = preSend(ctx, request, requestHeader);if (response.getCode() != -1) {return response;}final SendMessageResponseHeader responseHeader = (SendMessageResponseHeader) response.readCustomHeader();// 獲取消息體final byte[] body = request.getBody();// 發(fā)送消息時，是否指定消費(fèi)隊(duì)列，若沒有則隨機(jī)選擇int queueIdInt = requestHeader.getQueueId();// 獲取主題配置屬性TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());if (queueIdInt < 0) { // 隊(duì)列ID不符合，則在寫隊(duì)列隨機(jī)找個queueIdInt = randomQueueId(topicConfig.getWriteQueueNums());}MessageExtBrokerInner msgInner = new MessageExtBrokerInner();msgInner.setTopic(requestHeader.getTopic());msgInner.setQueueId(queueIdInt);// 消息擴(kuò)展屬性Map<String, String> oriProps = MessageDecoder.string2messageProperties(requestHeader.getProperties());// 消息是否進(jìn)入重試或延遲隊(duì)列中（重試次數(shù)失敗）if (!handleRetryAndDLQ(requestHeader, response, request, msgInner, topicConfig, oriProps)) {return response;}msgInner.setBody(body);msgInner.setFlag(requestHeader.getFlag());String uniqKey = oriProps.get(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX);if (uniqKey == null || uniqKey.length() <= 0) {uniqKey = MessageClientIDSetter.createUniqID();oriProps.put(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX, uniqKey);}MessageAccessor.setProperties(msgInner, oriProps);msgInner.setTagsCode(MessageExtBrokerInner.tagsString2tagsCode(topicConfig.getTopicFilterType(), msgInner.getTags()));msgInner.setBornTimestamp(requestHeader.getBornTimestamp());msgInner.setBornHost(ctx.channel().remoteAddress());msgInner.setStoreHost(this.getStoreHost());msgInner.setReconsumeTimes(requestHeader.getReconsumeTimes() == null ? 0 : requestHeader.getReconsumeTimes());String clusterName = this.brokerController.getBrokerConfig().getBrokerClusterName();MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_CLUSTER, clusterName);msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgInner.getProperties()));// Map<String, String> oriProps = MessageDecoder.string2messageProperties(requestHeader.getProperties());// 事務(wù)標(biāo)簽String traFlag = oriProps.get(MessageConst.PROPERTY_TRANSACTION_PREPARED);boolean sendTransactionPrepareMessage = false;if (Boolean.parseBoolean(traFlag)&& !(msgInner.getReconsumeTimes() > 0 && msgInner.getDelayTimeLevel() > 0)) { //For client under version 4.6.1// Broker禁止事務(wù)消息存儲if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) {response.setCode(ResponseCode.NO_PERMISSION);response.setRemark("the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1()+ "] sending transaction message is forbidden");return response;}sendTransactionPrepareMessage = true;}long beginTimeMillis = this.brokerController.getMessageStore().now();// 消息是否異步存儲if (brokerController.getBrokerConfig().isAsyncSendEnable()) {CompletableFuture<PutMessageResult> asyncPutMessageFuture;if (sendTransactionPrepareMessage) { // 事務(wù)prepare操作asyncPutMessageFuture = this.brokerController.getTransactionalMessageService().asyncPrepareMessage(msgInner);} else {asyncPutMessageFuture = this.brokerController.getMessageStore().asyncPutMessage(msgInner);}final int finalQueueIdInt = queueIdInt;final MessageExtBrokerInner finalMsgInner = msgInner;asyncPutMessageFuture.thenAcceptAsync(putMessageResult -> {RemotingCommand responseFuture =handlePutMessageResult(putMessageResult, response, request, finalMsgInner, responseHeader, sendMessageContext,ctx, finalQueueIdInt, beginTimeMillis, mappingContext);if (responseFuture != null) {doResponse(ctx, request, responseFuture);}sendMessageCallback.onComplete(sendMessageContext, response);}, this.brokerController.getPutMessageFutureExecutor());// Returns null to release the send message threadreturn null;}// 消息同步存儲else {PutMessageResult putMessageResult = null;// 事務(wù)消息存儲if (sendTransactionPrepareMessage) {putMessageResult = this.brokerController.getTransactionalMessageService().prepareMessage(msgInner);} else {// 同步存儲消息putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);}handlePutMessageResult(putMessageResult, response, request, msgInner, responseHeader, sendMessageContext, ctx, queueIdInt, beginTimeMillis, mappingContext);sendMessageCallback.onComplete(sendMessageContext, response);return response;}
}

三、消息存儲流程

1.?DefaultMessageStore類

????????org.apache.rocketmq.store.DefaultMessageStore是消息存儲實(shí)現(xiàn)類，也是存儲模塊最重要的一個類，其UML如下。

????????其關(guān)鍵屬性如下代碼所示。同步與異步存儲的方法：

• 同步消息：單個消息putMessage()、批量消息putMessages()
• 異步消息：單個消息asyncPutMessage()、批量消息asyncPutMessages()

// Commitlog引用次數(shù)
public final PerfCounter.Ticks perfs = new PerfCounter.Ticks(LOGGER);// 存儲配置屬性
private final MessageStoreConfig messageStoreConfig;
// CommitLog（Commitlog文件存儲實(shí)現(xiàn)類）
private final CommitLog commitLog;
// ConsumeQueue文件存儲實(shí)現(xiàn)類
private final ConsumeQueueStore consumeQueueStore;
// 刷盤線程
private final FlushConsumeQueueService flushConsumeQueueService;
// 刪除過期Commitlog文件服務(wù)
private final CleanCommitLogService cleanCommitLogService;
// 刪除過期ConsumeQueue文件服務(wù)
private final CleanConsumeQueueService cleanConsumeQueueService;
// 矯正邏輯偏移量服務(wù)
private final CorrectLogicOffsetService correctLogicOffsetService;
// index文件實(shí)現(xiàn)類
private final IndexService indexService;
// MappedFile分配服務(wù)
private final AllocateMappedFileService allocateMappedFileService;
// 消息提交到Commitlog時消息轉(zhuǎn)發(fā)，構(gòu)建ConsumeQueue、index文件服務(wù)
private ReputMessageService reputMessageService;
// HA服務(wù)（主從同步服務(wù)）
private HAService haService;
// 存儲狀態(tài)服務(wù)
private final StoreStatsService storeStatsService;
// 堆內(nèi)存緩存
private final TransientStorePool transientStorePool;// Broker狀態(tài)管理
private final BrokerStatsManager brokerStatsManager;
// 消息達(dá)到監(jiān)聽器（消息拉取長輪詢模式）
private final MessageArrivingListener messageArrivingListener;
// Broker配置屬性
private final BrokerConfig brokerConfig;
// 存儲刷盤檢查點(diǎn)
private StoreCheckpoint storeCheckpoint;
// 定時消息存儲實(shí)現(xiàn)類
private TimerMessageStore timerMessageStore;
// 日志打印次數(shù)
private AtomicLong printTimes = new AtomicLong(0);
// Commitlog文件轉(zhuǎn)發(fā)請求
private final LinkedList<CommitLogDispatcher> dispatcherList;// 延遲消息的延遲級別
private final ConcurrentMap<Integer /* level */, Long/* delay timeMillis */> delayLevelTable =new ConcurrentHashMap<Integer, Long>(32);// 最大延遲級別
private int maxDelayLevel;

2. 存儲流程

????????1)：同步與異步存儲

????????如下圖所示是同步與異步存儲的實(shí)現(xiàn)方法調(diào)用鏈，它們之間區(qū)別與聯(lián)系：

聯(lián)系：a. 同步存儲實(shí)際是調(diào)用異步存儲方法，即：DefaultMessageStore#asyncPutMessage;

? ? ? ? ? ?b. 最終執(zhí)行存儲方法是org.apache.rocketmq.store.CommitLog#asyncPutMessage；

區(qū)別：同步存儲需要等待存儲結(jié)果waitForPutResult()

????????2)：CommitLog異步存儲消息

????????org.apache.rocketmq.store.CommitLog#asyncPutMessage是異步執(zhí)行存儲消息。如下代碼所示，關(guān)鍵步驟如下：

• step1：mappedFileQueue隊(duì)列中，獲取可寫入的Commitlog，即：從commitlog目錄下獲取當(dāng)前寫入的Commitlog；
• step2：獲取當(dāng)前寫入Commitlog的偏移量 = 文件偏移量 + 該文件寫入位置；
• step3：是否需要HA（主從Broker同步數(shù)據(jù)）；
• step4：CommitLog.calMsgLength獲取該消息的總長度（不定長，總長度存儲在前4個字節(jié)）；
• step5：加鎖后（串行寫），判定再次Commitlog文件沒有或已被寫滿，則創(chuàng)建新的Commitlog文件；
• step6：Commit操作，即：消息緩存或直接（是否開啟堆外內(nèi)存池）追加到Commitlog文件內(nèi)存映射buffer，追加當(dāng)前消息，并沒有刷寫到磁盤，則返回結(jié)果，方法：{@link DefaultMappedFile#appendMessage}；
• step7：執(zhí)行同步或異步刷盤、HA主從同步復(fù)制等，方法：?{@link CommitLog#handleDiskFlushAndHA}。

/*** 執(zhí)行存儲消息* step1：mappedFileQueue隊(duì)列中，獲取可寫入的Commitlog，即：從commitlog目錄下獲取當(dāng)前寫入的Commitlog；* step2：獲取當(dāng)前寫入Commitlog的偏移量 = 文件偏移量 + 該文件寫入位置；* step3：是否需要HA（主從Broker同步數(shù)據(jù)）；* step4：CommitLog.calMsgLength獲取該消息的總長度（不定長，總長度存儲在前4個字節(jié)）；* step5：加鎖后（串行寫），判定再次Commitlog文件沒有或已被寫滿，則創(chuàng)建新的Commitlog文件；* step6：Commit操作，即：消息緩存或直接（是否開啟堆外內(nèi)存池）追加到Commitlog文件內(nèi)存映射buffer，追加當(dāng)前消息，并沒有刷寫到磁盤，則返回結(jié)果*       {@link DefaultMappedFile#appendMessage}* step7：執(zhí)行同步或異步刷盤、HA主從同步復(fù)制等*       {@link CommitLog#handleDiskFlushAndHA}* @param msg 消息* @return 存儲結(jié)果*/
public CompletableFuture<PutMessageResult> asyncPutMessage(final MessageExtBrokerInner msg) {// Set the storage timeif (!defaultMessageStore.getMessageStoreConfig().isDuplicationEnable()) {msg.setStoreTimestamp(System.currentTimeMillis());}// Set the message body CRC (consider the most appropriate setting on the client)msg.setBodyCRC(UtilAll.crc32(msg.getBody()));// Back to ResultsAppendMessageResult result = null;StoreStatsService storeStatsService = this.defaultMessageStore.getStoreStatsService();String topic = msg.getTopic();InetSocketAddress bornSocketAddress = (InetSocketAddress) msg.getBornHost();if (bornSocketAddress.getAddress() instanceof Inet6Address) {msg.setBornHostV6Flag();}InetSocketAddress storeSocketAddress = (InetSocketAddress) msg.getStoreHost();if (storeSocketAddress.getAddress() instanceof Inet6Address) {msg.setStoreHostAddressV6Flag();}PutMessageThreadLocal putMessageThreadLocal = this.putMessageThreadLocal.get();updateMaxMessageSize(putMessageThreadLocal);String topicQueueKey = generateKey(putMessageThreadLocal.getKeyBuilder(), msg);long elapsedTimeInLock = 0;// mappedFileQueue隊(duì)列中，獲取可寫入的Commitlog，即：從commitlog目錄下獲取當(dāng)前寫入的CommitlogMappedFile unlockMappedFile = null;MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile();// 當(dāng)前寫入Commitlog的偏移量long currOffset;if (mappedFile == null) {currOffset = 0;} else {// 當(dāng)前寫入Commitlog的偏移量 = 文件偏移量 + 該文件寫入位置currOffset = mappedFile.getFileFromOffset() + mappedFile.getWrotePosition();}// 是否需要HAint needAckNums = this.defaultMessageStore.getMessageStoreConfig().getInSyncReplicas();boolean needHandleHA = needHandleHA(msg);if (needHandleHA && this.defaultMessageStore.getBrokerConfig().isEnableControllerMode()) {if (this.defaultMessageStore.getHaService().inSyncReplicasNums(currOffset) < this.defaultMessageStore.getMessageStoreConfig().getMinInSyncReplicas()) {return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.IN_SYNC_REPLICAS_NOT_ENOUGH, null));}if (this.defaultMessageStore.getMessageStoreConfig().isAllAckInSyncStateSet()) {// -1 means all ack in SyncStateSetneedAckNums = MixAll.ALL_ACK_IN_SYNC_STATE_SET;}} else if (needHandleHA && this.defaultMessageStore.getBrokerConfig().isEnableSlaveActingMaster()) {int inSyncReplicas = Math.min(this.defaultMessageStore.getAliveReplicaNumInGroup(),this.defaultMessageStore.getHaService().inSyncReplicasNums(currOffset));needAckNums = calcNeedAckNums(inSyncReplicas);if (needAckNums > inSyncReplicas) {// Tell the producer, don't have enough slaves to handle the send requestreturn CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.IN_SYNC_REPLICAS_NOT_ENOUGH, null));}}topicQueueLock.lock(topicQueueKey);try {boolean needAssignOffset = true;if (defaultMessageStore.getMessageStoreConfig().isDuplicationEnable()&& defaultMessageStore.getMessageStoreConfig().getBrokerRole() != BrokerRole.SLAVE) {needAssignOffset = false;}if (needAssignOffset) {defaultMessageStore.assignOffset(msg, getMessageNum(msg));}/*當(dāng)前消息編碼，計算byteBuf（字節(jié)緩存）長度, null則正常處理CommitLog.calMsgLength獲取該消息的總長度（不定長，總長度存儲在前4個字節(jié)）*/PutMessageResult encodeResult = putMessageThreadLocal.getEncoder().encode(msg);if (encodeResult != null) {return CompletableFuture.completedFuture(encodeResult);}msg.setEncodedBuff(putMessageThreadLocal.getEncoder().getEncoderBuffer());PutMessageContext putMessageContext = new PutMessageContext(topicQueueKey);putMessageLock.lock(); //spin or ReentrantLock ,depending on store configtry {long beginLockTimestamp = this.defaultMessageStore.getSystemClock().now();this.beginTimeInLock = beginLockTimestamp;// Here settings are stored timestamp, in order to ensure an orderly// globalif (!defaultMessageStore.getMessageStoreConfig().isDuplicationEnable()) {msg.setStoreTimestamp(beginLockTimestamp); // 消息存儲時間戳，確保消息存儲有序}// Commitlog文件沒有或已被寫滿，則創(chuàng)建新的Commitlog文件if (null == mappedFile || mappedFile.isFull()) {// 創(chuàng)建新的Commitlog文件mappedFile = this.mappedFileQueue.getLastMappedFile(0); // Mark: NewFile may be cause noise}if (null == mappedFile) {log.error("create mapped file1 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());beginTimeInLock = 0;return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.CREATE_MAPPED_FILE_FAILED, null));}// Commitlog文件寫入消息（Commitlog文件內(nèi)存映射buffer，追加當(dāng)前消息，并沒有刷寫到磁盤，則返回結(jié)果）result = mappedFile.appendMessage(msg, this.appendMessageCallback, putMessageContext);switch (result.getStatus()) {case PUT_OK:onCommitLogAppend(msg, result, mappedFile);break;case END_OF_FILE:onCommitLogAppend(msg, result, mappedFile);unlockMappedFile = mappedFile;// Create a new file, re-write the messagemappedFile = this.mappedFileQueue.getLastMappedFile(0);if (null == mappedFile) {// XXX: warn and notify melog.error("create mapped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());beginTimeInLock = 0;return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.CREATE_MAPPED_FILE_FAILED, result));}result = mappedFile.appendMessage(msg, this.appendMessageCallback, putMessageContext);if (AppendMessageStatus.PUT_OK.equals(result.getStatus())) {onCommitLogAppend(msg, result, mappedFile);}break;case MESSAGE_SIZE_EXCEEDED:case PROPERTIES_SIZE_EXCEEDED:beginTimeInLock = 0;return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, result));case UNKNOWN_ERROR:beginTimeInLock = 0;return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result));default:beginTimeInLock = 0;return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result));}elapsedTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp;beginTimeInLock = 0;} finally {putMessageLock.unlock();}} finally {topicQueueLock.unlock(topicQueueKey);}// putMessage加鎖超時if (elapsedTimeInLock > 500) {log.warn("[NOTIFYME]putMessage in lock cost time(ms)={}, bodyLength={} AppendMessageResult={}", elapsedTimeInLock, msg.getBody().length, result);}if (null != unlockMappedFile && this.defaultMessageStore.getMessageStoreConfig().isWarmMapedFileEnable()) {this.defaultMessageStore.unlockMappedFile(unlockMappedFile);}PutMessageResult putMessageResult = new PutMessageResult(PutMessageStatus.PUT_OK, result);// StatisticsstoreStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).add(result.getMsgNum());storeStatsService.getSinglePutMessageTopicSizeTotal(topic).add(result.getWroteBytes());/*執(zhí)行同步或異步刷盤、HA主從同步復(fù)制等注意：MappedFile.appendMessage只是將消息追加到Commitlog文件內(nèi)存映射buffer中，并沒有刷寫到磁盤，則返回結(jié)果*/return handleDiskFlushAndHA(putMessageResult, msg, needAckNums, needHandleHA);
}

????????3)：提交消息（Commit）

????????org.apache.rocketmq.store.logfile.DefaultMappedFile#appendMessage是文件內(nèi)存映射追加消息方法，目的是把堆外緩存池消息或直接Commit到文件內(nèi)存映射，其調(diào)用鏈如下。

????????org.apache.rocketmq.store.logfile.DefaultMappedFile#appendMessagesInner是追加消息到文件內(nèi)存映射的核心方法，如下代碼所示。

/*** Commit操作，即：消息緩存或直接（是否開啟堆外內(nèi)存池）追加到Commitlog文件內(nèi)存映射buffer，追加當(dāng)前消息，并沒有刷寫到磁盤，則返回結(jié)果* step1：當(dāng)前Commitlog的寫指針，判斷文件是否寫滿；* step2：slice()：創(chuàng)建與原ByteBuffer共享的內(nèi)存區(qū)，擁有獨(dú)立的position、limit、capacity等指針，并設(shè)置position當(dāng)前寫指針* step3：判斷是否是批量消息，并追加消息到Commitlog文件內(nèi)存映射buffer，并沒有刷寫到磁盤，則返回結(jié)果*/
public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb,PutMessageContext putMessageContext) {assert messageExt != null;assert cb != null;// 當(dāng)前Commitlog的寫指針int currentPos = WROTE_POSITION_UPDATER.get(this);// 未寫滿，則追加if (currentPos < this.fileSize) {/*slice()：創(chuàng)建與原ByteBuffer共享的內(nèi)存區(qū)，擁有獨(dú)立的position、limit、capacity等指針并設(shè)置position當(dāng)前寫指針*/ByteBuffer byteBuffer = appendMessageBuffer().slice();byteBuffer.position(currentPos);AppendMessageResult result;// 批量消息if (messageExt instanceof MessageExtBatch && !((MessageExtBatch) messageExt).isInnerBatch()) {// traditional batch message// Commitlog文件內(nèi)存映射buffer，追加當(dāng)前消息，并沒有刷寫到磁盤，則返回結(jié)果result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos,(MessageExtBatch) messageExt, putMessageContext);}// 單個消息else if (messageExt instanceof MessageExtBrokerInner) {// traditional single message or newly introduced inner-batch message// Commitlog文件內(nèi)存映射buffer，追加當(dāng)前消息，并沒有刷寫到磁盤，則返回結(jié)果result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos,(MessageExtBrokerInner) messageExt, putMessageContext);} else {return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);}WROTE_POSITION_UPDATER.addAndGet(this, result.getWroteBytes());this.storeTimestamp = result.getStoreTimestamp();return result;}log.error("MappedFile.appendMessage return null, wrotePosition: {} fileSize: {}", currentPos, this.fileSize);return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
}

? ? ? ? 需要注意的是：appendMessageBuffer().slice()，創(chuàng)建與原ByteBuffer共享的內(nèi)存區(qū)，擁有獨(dú)立的position、limit、capacity等指針，并設(shè)置position當(dāng)前寫指針。創(chuàng)建的內(nèi)存追加消息。

四、參考資料

Rocket Mq消息持久化_飛科-程序人生的博客-CSDN博客

百度安全驗(yàn)證

【RocketMQ】同一個項(xiàng)目中，同一個topic，可以存在多個消費(fèi)者么？ - N!CE波 - 博客園

RocketMQ5.0.0消息發(fā)送_愛我所愛0505的博客-CSDN博客

RocketMQ5.0.0路由中心NameServer_愛我所愛0505的博客-CSDN博客

RocketMQ5.0.0消息存儲＜一＞_存儲文件及內(nèi)存映射_愛我所愛0505的博客-CSDN博客?