RocketMQ作為訊息中介軟體，經常會被用來和其他訊息中介軟體做比較，比對rabbitmq, kafka... 但個人覺得它一直對標的，都是kafka。因為它們面對的場景往往都是超高併發，超高效能要求的場景。
所以，有必要深挖下其實現高效能，高併發的原因。實際上，這是非常大的話題，我這裡也不打算一口吃個大胖子。我會給出個大概答案，然後我們再深入挖掘其中部分實現。如題所述。
1. 高效能高併發系統的底層技能概述
我不打算單講rocketmq到底是如何實現高效能高併發的，因為實際上的底層原則都是差不多的。rocketmq不過是其中的一個實現者而已。
那麼，要想實現高效能高併發，大概需要怎麼做的呢？本質上講，我們的系統服務能利用的東西並不多，CPU、記憶體、磁碟、網路、硬體特性。。。 當然了，還有一個非常重要的東西，就是我們基本都是在做應用層服務，所以我們的能力往往必須依託於作業系統提供的服務，由這些服務去更好地利用底層硬體的東西。好吧，顯得逼格好像有點高了，實際上就是一個系統API呼叫。
接下來，我們從每個小點出發，來看看我們如何做到高效能高併發：
第一個：CPU。可以說，CPU代表了單機的極限。如果能夠做有效利用CPU, 使其隨時可保證在80%以上的使用率，那麼你這個服務絕對夠牛逼了（注意不是導致瘋狂GC的那種利用率哦）。那麼，我們如何做到高效利用CPU呢？有些應用天然就是CPU型的，比如提供一些做大數的運算服務，天生就需要大量CPU運算。而其他的很多的IO型的應用，則CPU往往不會太高，或者說我們應該往高了的方向優化。
第二個：記憶體。記憶體是一個非常寶貴的資源，因為記憶體的排程速度非常快。如果一個應用的業務處理都是基於記憶體的，那麼這個應用基本上就會超級強悍。大部分情況下，越大的記憶體往往也能提供越高的效能，比如ES的搜尋服務，要想效能好必需有足夠記憶體。當然了，記憶體除了使用起來非常方便之外，它還有一個重要的工作，就是記憶體的回收。當然，這部分工作一般都會被程式語言遮蔽掉，因為它實在太難了。我們一般只需按照語言特性，合理的處理物件即可。另外，我們可以使一些可能需要從外部裝置讀入的資料，載入到記憶體中長期使用，這將是一件非常重要的優化動作。如何維護好資料一致性與安全性和準確性，是這類工作的重點。
第三個：磁碟。記憶體雖好，但卻不常有。記憶體往往意味著大小受限。而與之對應的就是磁碟，磁碟則往往意味空間非常大，資料永久儲存安全。磁碟基本上就代表了單機的儲存極限，但也同時限制了併發能力。
第四個：網路。也許這個名詞不太合適，但卻是因為網路才發生了變化。如果說前面講的都是單機的極限效能，那麼，網路就會帶來分散式系統的極限效能。一個龐大的系統，一定是分散式的，因此必然會使用到網路這個裝置。但我們一般不會在這上面節省多少東西，我們能做的，也許就是簡單的壓縮下檔案資料而已。更多的，也許我們只是申請更大的頻寬，或者開闢新的佈線，以滿足系統的需要。在網路這一環境，如何更好地組織網路裝置，是重中之重，而這往往又回到了上面三個話題之一了。
最後，排除上面幾個硬技能，還有一個也是非常重要的技能：那就是演算法，沒有好的演算法，再多的優化可能也只是杯水車薪。（當然了我們大部分情況下是無需高階演算法的，因為大部分時間，我們只是大自然的搬運工）
2. 高效能高併發作業系統api列舉
前面說的，更多是理論上講如何形成牛逼的應用服務。但我們又沒那能力去搞作業系統的東西，所以也只能想想而已。那麼說到底，我們能做什麼呢？所謂工欲善其事，必先利其器。所謂利器，也就是看看作業系統提供什麼樣的底層API 。
我這裡就稍微列幾個吧（我也就知道這麼些了）：
epoll系列: IO多路複用技術，高併發高效能網路應用必備。大致作用就是使用極少數的執行緒，高效地管理大量io事件，通知應用等。大概的介面有: epoll_create(), epoll_ctl(), epoll_wait();
pagecache系列: 作業系統頁快取，高效讀寫檔案必備。大致作用就是保留部分磁碟資料在記憶體中，以便應用想讀取或者磁碟資料資料時能夠非常快速的響應。相關介面如: read(), write(), readpage(), writepage(), sync(), fsync().
mmap系列: 記憶體對映。可以將檔案對映到記憶體中，使用者寫資料時直接向該記憶體緩衝區寫資料，即可達到寫磁碟的作用了，從而提高寫入效能。介面如: mmap(), munmap();
directio系列: 直接io操作，避免使用者態資料到核心態資料的相互copy, 節省cpu和記憶體佔用。
cas系列: 高效安全鎖實現。相關介面: cmpxchg() 。
多執行緒系列: 大部分網路應用，都io型的，那麼如何同時處理多個請求就非常重要了。多執行緒提供非常便捷的併發程式設計基礎，使得我們可以更簡單的處理業務而且提供超高的處理能力。這自然是程式語言直接提供的。
3. rocketmq中的高效能法寶
rocketmq想要實現高併發高效能處理能力，自然要從作業系統層面去尋求方法，自然也就逃不過前面的幾點說法了。
首先，它基於netty實現了高效能的網路通訊，netty基於事件的io模型，零拷貝的技術，已經提供了非常好的技術前提，rocketmq只需利用一下，就可以將自己變得很厲害了。當然，這只是其厲害的一個點，因為單有了高效網路通訊處理能力還不夠的。至少，rocketmq得提供高效的資料序列化方式。
其次，有了netty作為通訊框架，高效接入請求後，rocketmq自身處理業務的方式非常重要。如果能夠直接基於記憶體儲存資料，那必然是最高效能的。但是它不能那樣做，因為記憶體太小，無法容納下應有的訊息。所以，只能基於檔案做儲存。而檔案本身的操作又是代價非常高的，所以，必須要有些稍微的措施，避免重量級的操作檔案。所以，檔案的多級儲存又是非常重要的了，即如索引檔案在db中的應用就知道了。
再其次，java提供了非常好的多執行緒程式設計環境，不加以利用就對不起觀眾了。良好的執行緒模型，為其高效能吶喊助威。
最後，基於pagecache和mmap的高效檔案讀寫，才是其制勝法寶。這也是我們接下來想要重點說明的。
4. rocketmq中對mmap和pagecache的應用
上一點中提到的每個點，都是rocketmq出眾的原因，但我們今天只會來說一點：rocketmq的高效檔案儲存。
實際上，根據我之前的幾篇文章，我們很容易找到rocketmq是如何對檔案進行讀寫的。我們就以producer寫訊息資料為例，來回顧看看rmq是如何進行高效檔案儲存的。
// 處理器入口 // org.apache.rocketmq.broker.processor.SendMessageProcessor#processRequest @Override public RemotingCommand processRequest(ChannelHandlerContext ctx, RemotingCommand request) throws RemotingCommandException { RemotingCommand response = null; try { response = asyncProcessRequest(ctx, request).get(); } catch (InterruptedException | ExecutionException e) { log.error("process SendMessage error, request : " + request.toString(), e); } return response; } // 接收轉發，非同步處理 public CompletableFuture<RemotingCommand> asyncProcessRequest(ChannelHandlerContext ctx, RemotingCommand request) throws RemotingCommandException { final SendMessageContext mqtraceContext; switch (request.getCode()) { case RequestCode.CONSUMER_SEND_MSG_BACK: return this.asyncConsumerSendMsgBack(ctx, request); default: // 寫入資料 SendMessageRequestHeader requestHeader = parseRequestHeader(request); if (requestHeader == null) { return CompletableFuture.completedFuture(null); } mqtraceContext = buildMsgContext(ctx, requestHeader); this.executeSendMessageHookBefore(ctx, request, mqtraceContext); if (requestHeader.isBatch()) { return this.asyncSendBatchMessage(ctx, request, mqtraceContext, requestHeader); } else { return this.asyncSendMessage(ctx, request, mqtraceContext, requestHeader); } } } // org.apache.rocketmq.store.CommitLog#putMessage public PutMessageResult putMessage(final MessageExtBrokerInner msg) { // Set the storage time msg.setStoreTimestamp(System.currentTimeMillis()); // Set the message body BODY CRC (consider the most appropriate setting // on the client) msg.setBodyCRC(UtilAll.crc32(msg.getBody())); // Back to Results AppendMessageResult result = null; StoreStatsService storeStatsService = this.defaultMessageStore.getStoreStatsService(); String topic = msg.getTopic(); int queueId = msg.getQueueId(); final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag()); if (tranType == MessageSysFlag.TRANSACTION_NOT_TYPE || tranType == MessageSysFlag.TRANSACTION_COMMIT_TYPE) { // Delay Delivery if (msg.getDelayTimeLevel() > 0) { if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) { msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()); } topic = TopicValidator.RMQ_SYS_SCHEDULE_TOPIC; queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel()); // Backup real topic, queueId MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_TOPIC, msg.getTopic()); MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_QUEUE_ID, String.valueOf(msg.getQueueId())); msg.setPropertiesString(MessageDecoder.messageProperties2String(msg.getProperties())); msg.setTopic(topic); msg.setQueueId(queueId); } } InetSocketAddress bornSocketAddress = (InetSocketAddress) msg.getBornHost(); if (bornSocketAddress.getAddress() instanceof Inet6Address) { msg.setBornHostV6Flag(); } InetSocketAddress storeSocketAddress = (InetSocketAddress) msg.getStoreHost(); if (storeSocketAddress.getAddress() instanceof Inet6Address) { msg.setStoreHostAddressV6Flag(); } long elapsedTimeInLock = 0; MappedFile unlockMappedFile = null; MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile(); putMessageLock.lock(); //spin or ReentrantLock ,depending on store config try { long beginLockTimestamp = this.defaultMessageStore.getSystemClock().now(); this.beginTimeInLock = beginLockTimestamp; // Here settings are stored timestamp, in order to ensure an orderly // global msg.setStoreTimestamp(beginLockTimestamp); if (null == mappedFile || mappedFile.isFull()) { 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 new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, null); } result = mappedFile.appendMessage(msg, this.appendMessageCallback); switch (result.getStatus()) { case PUT_OK: break; case END_OF_FILE: unlockMappedFile = mappedFile; // Create a new file, re-write the message mappedFile = this.mappedFileQueue.getLastMappedFile(0); if (null == mappedFile) { // XXX: warn and notify me log.error("create mapped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString()); beginTimeInLock = 0; return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result); } result = mappedFile.appendMessage(msg, this.appendMessageCallback); break; case MESSAGE_SIZE_EXCEEDED: case PROPERTIES_SIZE_EXCEEDED: beginTimeInLock = 0; return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, result); case UNKNOWN_ERROR: beginTimeInLock = 0; return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result); default: beginTimeInLock = 0; return new PutMessageResult(PutMessageStatus.UNKNOWN_ERROR, result); } elapsedTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp; beginTimeInLock = 0; } finally { putMessageLock.unlock(); } 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); // Statistics storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).incrementAndGet(); storeStatsService.getSinglePutMessageTopicSizeTotal(topic).addAndGet(result.getWroteBytes()); handleDiskFlush(result, putMessageResult, msg); handleHA(result, putMessageResult, msg); return putMessageResult; } // org.apache.rocketmq.broker.processor.SendMessageProcessor#asyncSendMessage private CompletableFuture<RemotingCommand> asyncSendMessage(ChannelHandlerContext ctx, RemotingCommand request, SendMessageContext mqtraceContext, SendMessageRequestHeader requestHeader) { final RemotingCommand response = preSend(ctx, request, requestHeader); final SendMessageResponseHeader responseHeader = (SendMessageResponseHeader)response.readCustomHeader(); if (response.getCode() != -1) { return CompletableFuture.completedFuture(response); } final byte[] body = request.getBody(); int queueIdInt = requestHeader.getQueueId(); TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic()); if (queueIdInt < 0) { queueIdInt = randomQueueId(topicConfig.getWriteQueueNums()); } MessageExtBrokerInner msgInner = new MessageExtBrokerInner(); msgInner.setTopic(requestHeader.getTopic()); msgInner.setQueueId(queueIdInt); if (!handleRetryAndDLQ(requestHeader, response, request, msgInner, topicConfig)) { return CompletableFuture.completedFuture(response); } msgInner.setBody(body); msgInner.setFlag(requestHeader.getFlag()); MessageAccessor.setProperties(msgInner, MessageDecoder.string2messageProperties(requestHeader.getProperties())); msgInner.setPropertiesString(requestHeader.getProperties()); 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())); CompletableFuture<PutMessageResult> putMessageResult = null; Map<String, String> origProps = MessageDecoder.string2messageProperties(requestHeader.getProperties()); String transFlag = origProps.get(MessageConst.PROPERTY_TRANSACTION_PREPARED); if (transFlag != null && Boolean.parseBoolean(transFlag)) { if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) { response.setCode(ResponseCode.NO_PERMISSION); response.setRemark( "the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1() + "] sending transaction message is forbidden"); return CompletableFuture.completedFuture(response); } putMessageResult = this.brokerController.getTransactionalMessageService().asyncPrepareMessage(msgInner); } else { // 簡單起見，我們只看非事務的訊息寫入 putMessageResult = this.brokerController.getMessageStore().asyncPutMessage(msgInner); } return handlePutMessageResultFuture(putMessageResult, response, request, msgInner, responseHeader, mqtraceContext, ctx, queueIdInt); } // org.apache.rocketmq.store.DefaultMessageStore#asyncPutMessage @Override public CompletableFuture<PutMessageResult> asyncPutMessage(MessageExtBrokerInner msg) { PutMessageStatus checkStoreStatus = this.checkStoreStatus(); if (checkStoreStatus != PutMessageStatus.PUT_OK) { return CompletableFuture.completedFuture(new PutMessageResult(checkStoreStatus, null)); } PutMessageStatus msgCheckStatus = this.checkMessage(msg); if (msgCheckStatus == PutMessageStatus.MESSAGE_ILLEGAL) { return CompletableFuture.completedFuture(new PutMessageResult(msgCheckStatus, null)); } // 寫入訊息資料到commitLog中 long beginTime = this.getSystemClock().now(); CompletableFuture<PutMessageResult> putResultFuture = this.commitLog.asyncPutMessage(msg); putResultFuture.thenAccept((result) -> { long elapsedTime = this.getSystemClock().now() - beginTime; if (elapsedTime > 500) { log.warn("putMessage not in lock elapsed time(ms)={}, bodyLength={}", elapsedTime, msg.getBody().length); } this.storeStatsService.setPutMessageEntireTimeMax(elapsedTime); if (null == result || !result.isOk()) { this.storeStatsService.getPutMessageFailedTimes().incrementAndGet(); } }); return putResultFuture; } // 寫入訊息資料到commitLog中 // org.apache.rocketmq.store.CommitLog#asyncPutMessage public CompletableFuture<PutMessageResult> asyncPutMessage(final MessageExtBrokerInner msg) { // Set the storage time msg.setStoreTimestamp(System.currentTimeMillis()); // Set the message body BODY CRC (consider the most appropriate setting // on the client) msg.setBodyCRC(UtilAll.crc32(msg.getBody())); // Back to Results AppendMessageResult result = null; StoreStatsService storeStatsService = this.defaultMessageStore.getStoreStatsService(); String topic = msg.getTopic(); int queueId = msg.getQueueId(); final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag()); if (tranType == MessageSysFlag.TRANSACTION_NOT_TYPE || tranType == MessageSysFlag.TRANSACTION_COMMIT_TYPE) { // Delay Delivery if (msg.getDelayTimeLevel() > 0) { if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) { msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()); } topic = TopicValidator.RMQ_SYS_SCHEDULE_TOPIC; queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel()); // Backup real topic, queueId MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_TOPIC, msg.getTopic()); MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_QUEUE_ID, String.valueOf(msg.getQueueId())); msg.setPropertiesString(MessageDecoder.messageProperties2String(msg.getProperties())); msg.setTopic(topic); msg.setQueueId(queueId); } } long elapsedTimeInLock = 0; // 獲取mappedFile例項，後續將向其寫入資料 MappedFile unlockMappedFile = null; MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile(); // 上鎖寫資料，保證資料寫入安全準確 putMessageLock.lock(); //spin or ReentrantLock ,depending on store config try { long beginLockTimestamp = this.defaultMessageStore.getSystemClock().now(); this.beginTimeInLock = beginLockTimestamp; // Here settings are stored timestamp, in order to ensure an orderly // global msg.setStoreTimestamp(beginLockTimestamp); // 確保mappedFile有效 if (null == mappedFile || mappedFile.isFull()) { 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_MAPEDFILE_FAILED, null)); } // 向mappedFile中追加資料，完成寫入動作 result = mappedFile.appendMessage(msg, this.appendMessageCallback); switch (result.getStatus()) { case PUT_OK: break; case END_OF_FILE: unlockMappedFile = mappedFile; // Create a new file, re-write the message mappedFile = this.mappedFileQueue.getLastMappedFile(0); if (null == mappedFile) { // XXX: warn and notify me log.error("create mapped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString()); beginTimeInLock = 0; return CompletableFuture.completedFuture(new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result)); } result = mappedFile.appendMessage(msg, this.appendMessageCallback); 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(); } 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); // Statistics storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).incrementAndGet(); storeStatsService.getSinglePutMessageTopicSizeTotal(topic).addAndGet(result.getWroteBytes()); CompletableFuture<PutMessageStatus> flushResultFuture = submitFlushRequest(result, putMessageResult, msg); CompletableFuture<PutMessageStatus> replicaResultFuture = submitReplicaRequest(result, putMessageResult, msg); return flushResultFuture.thenCombine(replicaResultFuture, (flushStatus, replicaStatus) -> { if (flushStatus != PutMessageStatus.PUT_OK) { putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT); } if (replicaStatus != PutMessageStatus.PUT_OK) { putMessageResult.setPutMessageStatus(replicaStatus); } return putMessageResult; }); } // 獲取有效的mappedFile例項 // org.apache.rocketmq.store.MappedFileQueue#getLastMappedFile() public MappedFile getLastMappedFile() { MappedFile mappedFileLast = null; while (!this.mappedFiles.isEmpty()) { try { mappedFileLast = this.mappedFiles.get(this.mappedFiles.size() - 1); break; } catch (IndexOutOfBoundsException e) { //continue; } catch (Exception e) { log.error("getLastMappedFile has exception.", e); break; } } return mappedFileLast; } // 再次嘗試獲取 mappedFile, 沒有則建立一個新的 // org.apache.rocketmq.store.MappedFileQueue#getLastMappedFile(long) public MappedFile getLastMappedFile(final long startOffset) { return getLastMappedFile(startOffset, true); } public MappedFile getLastMappedFile(final long startOffset, boolean needCreate) { long createOffset = -1; MappedFile mappedFileLast = getLastMappedFile(); if (mappedFileLast == null) { createOffset = startOffset - (startOffset % this.mappedFileSize); } if (mappedFileLast != null && mappedFileLast.isFull()) { createOffset = mappedFileLast.getFileFromOffset() + this.mappedFileSize; } if (createOffset != -1 && needCreate) { String nextFilePath = this.storePath + File.separator + UtilAll.offset2FileName(createOffset); String nextNextFilePath = this.storePath + File.separator + UtilAll.offset2FileName(createOffset + this.mappedFileSize); MappedFile mappedFile = null; // 分配建立一個新的commitLog檔案 if (this.allocateMappedFileService != null) { mappedFile = this.allocateMappedFileService.putRequestAndReturnMappedFile(nextFilePath, nextNextFilePath, this.mappedFileSize); } else { try { mappedFile = new MappedFile(nextFilePath, this.mappedFileSize); } catch (IOException e) { log.error("create mappedFile exception", e); } } if (mappedFile != null) { if (this.mappedFiles.isEmpty()) { mappedFile.setFirstCreateInQueue(true); } this.mappedFiles.add(mappedFile); } return mappedFile; } return mappedFileLast; } // 向commitLog中得到的mappedFile順序寫入資料 public AppendMessageResult appendMessage(final MessageExtBrokerInner msg, final AppendMessageCallback cb) { return appendMessagesInner(msg, cb); } public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb) { assert messageExt != null; assert cb != null; int currentPos = this.wrotePosition.get(); if (currentPos < this.fileSize) { ByteBuffer byteBuffer = writeBuffer != null ? writeBuffer.slice() : this.mappedByteBuffer.slice(); byteBuffer.position(currentPos); AppendMessageResult result; if (messageExt instanceof MessageExtBrokerInner) { // 回撥，寫入資料到 commitLog 中 // 將資料寫入 byteBuffer, 即將資料寫入了pagecache, 也就寫入了磁碟檔案中了 result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBrokerInner) messageExt); } else if (messageExt instanceof MessageExtBatch) { result = cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, (MessageExtBatch) messageExt); } else { return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR); } this.wrotePosition.addAndGet(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); } // org.apache.rocketmq.store.CommitLog.DefaultAppendMessageCallback#doAppend(long, java.nio.ByteBuffer, int, org.apache.rocketmq.store.MessageExtBrokerInner) public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank, final MessageExtBrokerInner msgInner) { // STORETIMESTAMP + STOREHOSTADDRESS + OFFSET <br> // PHY OFFSET long wroteOffset = fileFromOffset + byteBuffer.position(); int sysflag = msgInner.getSysFlag(); int bornHostLength = (sysflag & MessageSysFlag.BORNHOST_V6_FLAG) == 0 ? 4 + 4 : 16 + 4; int storeHostLength = (sysflag & MessageSysFlag.STOREHOSTADDRESS_V6_FLAG) == 0 ? 4 + 4 : 16 + 4; ByteBuffer bornHostHolder = ByteBuffer.allocate(bornHostLength); ByteBuffer storeHostHolder = ByteBuffer.allocate(storeHostLength); this.resetByteBuffer(storeHostHolder, storeHostLength); String msgId; if ((sysflag & MessageSysFlag.STOREHOSTADDRESS_V6_FLAG) == 0) { msgId = MessageDecoder.createMessageId(this.msgIdMemory, msgInner.getStoreHostBytes(storeHostHolder), wroteOffset); } else { msgId = MessageDecoder.createMessageId(this.msgIdV6Memory, msgInner.getStoreHostBytes(storeHostHolder), wroteOffset); } // Record ConsumeQueue information keyBuilder.setLength(0); keyBuilder.append(msgInner.getTopic()); keyBuilder.append('-'); keyBuilder.append(msgInner.getQueueId()); String key = keyBuilder.toString(); Long queueOffset = CommitLog.this.topicQueueTable.get(key); // 初始化queueId資訊 if (null == queueOffset) { queueOffset = 0L; CommitLog.this.topicQueueTable.put(key, queueOffset); } // Transaction messages that require special handling final int tranType = MessageSysFlag.getTransactionValue(msgInner.getSysFlag()); switch (tranType) { // Prepared and Rollback message is not consumed, will not enter the // consumer queuec case MessageSysFlag.TRANSACTION_PREPARED_TYPE: case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE: queueOffset = 0L; break; case MessageSysFlag.TRANSACTION_NOT_TYPE: case MessageSysFlag.TRANSACTION_COMMIT_TYPE: default: break; } /** * Serialize message */ final byte[] propertiesData = msgInner.getPropertiesString() == null ? null : msgInner.getPropertiesString().getBytes(MessageDecoder.CHARSET_UTF8); final int propertiesLength = propertiesData == null ? 0 : propertiesData.length; if (propertiesLength > Short.MAX_VALUE) { log.warn("putMessage message properties length too long. length={}", propertiesData.length); return new AppendMessageResult(AppendMessageStatus.PROPERTIES_SIZE_EXCEEDED); } final byte[] topicData = msgInner.getTopic().getBytes(MessageDecoder.CHARSET_UTF8); final int topicLength = topicData.length; final int bodyLength = msgInner.getBody() == null ? 0 : msgInner.getBody().length; final int msgLen = calMsgLength(msgInner.getSysFlag(), bodyLength, topicLength, propertiesLength); // Exceeds the maximum message if (msgLen > this.maxMessageSize) { CommitLog.log.warn("message size exceeded, msg total size: " + msgLen + ", msg body size: " + bodyLength + ", maxMessageSize: " + this.maxMessageSize); return new AppendMessageResult(AppendMessageStatus.MESSAGE_SIZE_EXCEEDED); } // Determines whether there is sufficient free space if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) { this.resetByteBuffer(this.msgStoreItemMemory, maxBlank); // 1 TOTALSIZE this.msgStoreItemMemory.putInt(maxBlank); // 2 MAGICCODE this.msgStoreItemMemory.putInt(CommitLog.BLANK_MAGIC_CODE); // 3 The remaining space may be any value // Here the length of the specially set maxBlank final long beginTimeMills = CommitLog.this.defaultMessageStore.now(); byteBuffer.put(this.msgStoreItemMemory.array(), 0, maxBlank); return new AppendMessageResult(AppendMessageStatus.END_OF_FILE, wroteOffset, maxBlank, msgId, msgInner.getStoreTimestamp(), queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills); } // 序列化寫入資料，寫header... body... // Initialization of storage space this.resetByteBuffer(msgStoreItemMemory, msgLen); // 1 TOTALSIZE this.msgStoreItemMemory.putInt(msgLen); // 2 MAGICCODE this.msgStoreItemMemory.putInt(CommitLog.MESSAGE_MAGIC_CODE); // 3 BODYCRC this.msgStoreItemMemory.putInt(msgInner.getBodyCRC()); // 4 QUEUEID this.msgStoreItemMemory.putInt(msgInner.getQueueId()); // 5 FLAG this.msgStoreItemMemory.putInt(msgInner.getFlag()); // 6 QUEUEOFFSET this.msgStoreItemMemory.putLong(queueOffset); // 7 PHYSICALOFFSET this.msgStoreItemMemory.putLong(fileFromOffset + byteBuffer.position()); // 8 SYSFLAG this.msgStoreItemMemory.putInt(msgInner.getSysFlag()); // 9 BORNTIMESTAMP this.msgStoreItemMemory.putLong(msgInner.getBornTimestamp()); // 10 BORNHOST this.resetByteBuffer(bornHostHolder, bornHostLength); this.msgStoreItemMemory.put(msgInner.getBornHostBytes(bornHostHolder)); // 11 STORETIMESTAMP this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp()); // 12 STOREHOSTADDRESS this.resetByteBuffer(storeHostHolder, storeHostLength); this.msgStoreItemMemory.put(msgInner.getStoreHostBytes(storeHostHolder)); // 13 RECONSUMETIMES this.msgStoreItemMemory.putInt(msgInner.getReconsumeTimes()); // 14 Prepared Transaction Offset this.msgStoreItemMemory.putLong(msgInner.getPreparedTransactionOffset()); // 15 BODY this.msgStoreItemMemory.putInt(bodyLength); if (bodyLength > 0) this.msgStoreItemMemory.put(msgInner.getBody()); // 16 TOPIC this.msgStoreItemMemory.put((byte) topicLength); this.msgStoreItemMemory.put(topicData); // 17 PROPERTIES this.msgStoreItemMemory.putShort((short) propertiesLength); if (propertiesLength > 0) this.msgStoreItemMemory.put(propertiesData); final long beginTimeMills = CommitLog.this.defaultMessageStore.now(); // Write messages to the queue buffer // 將資料寫入 ByteBuffer 中， byteBuffer.put(this.msgStoreItemMemory.array(), 0, msgLen); AppendMessageResult result = new AppendMessageResult(AppendMessageStatus.PUT_OK, wroteOffset, msgLen, msgId, msgInner.getStoreTimestamp(), queueOffset, CommitLog.this.defaultMessageStore.now() - beginTimeMills); switch (tranType) { case MessageSysFlag.TRANSACTION_PREPARED_TYPE: case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE: break; case MessageSysFlag.TRANSACTION_NOT_TYPE: case MessageSysFlag.TRANSACTION_COMMIT_TYPE: // The next update ConsumeQueue information CommitLog.this.topicQueueTable.put(key, ++queueOffset); break; default: break; } return result; }
以上過程看似複雜，實則只有最後一個bytebuffer.putXxx() 是真正的和mappedFile 是相關的。當然了，還有MappedFile的初始過程，它會先嚐試從現有開啟的mappFiles中獲取最後一個例項，如果mappedFile滿了之後，就會嘗試建立一個新的mappedFile, 這個過程一般伴隨著新的commitLog檔案的建立。
mappedFile 的刷盤動作，主要分為同步刷盤和非同步刷，底層都是一樣的，即呼叫 flush(),MappedFileChannel.force(), 將pagecache強制刷入到磁碟上。一般地，將資料寫入pagecache，基本就能保證不丟失了。但還是有例外情況，比如機器掉電，或者系統bug這種極端情況，還是會導致丟資料喲。
下面大致來看看 mappedFile 同步刷盤過程：
// org.apache.rocketmq.store.CommitLog#handleDiskFlush public void handleDiskFlush(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) { // Synchronization flush // 同步刷盤 if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) { final GroupCommitService service = (GroupCommitService) this.flushCommitLogService; if (messageExt.isWaitStoreMsgOK()) { // 提交一個刷盤任務到 GroupCommitService, 同步等待結果響應 GroupCommitRequest request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes()); service.putRequest(request); CompletableFuture<PutMessageStatus> flushOkFuture = request.future(); PutMessageStatus flushStatus = null; try { flushStatus = flushOkFuture.get(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout(), TimeUnit.MILLISECONDS); } catch (InterruptedException | ExecutionException | TimeoutException e) { //flushOK=false; } if (flushStatus != PutMessageStatus.PUT_OK) { log.error("do groupcommit, wait for flush failed, topic: " + messageExt.getTopic() + " tags: " + messageExt.getTags() + " client address: " + messageExt.getBornHostString()); putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT); } } else { service.wakeup(); } } // Asynchronous flush // 非同步刷盤 else { // 非同步刷盤則直接喚醒一個刷盤執行緒即可 if (!this.defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) { flushCommitLogService.wakeup(); } else { commitLogService.wakeup(); } } } // org.apache.rocketmq.store.CommitLog.GroupCommitService#putRequest // 新增刷盤請求 public synchronized void putRequest(final GroupCommitRequest request) { synchronized (this.requestsWrite) { this.requestsWrite.add(request); } this.wakeup(); } // 刷盤執行緒一直執行 public void run() { CommitLog.log.info(this.getServiceName() + " service started"); while (!this.isStopped()) { try { this.waitForRunning(10); // 執行真正的刷動作 this.doCommit(); } catch (Exception e) { CommitLog.log.warn(this.getServiceName() + " service has exception. ", e); } } // Under normal circumstances shutdown, wait for the arrival of the // request, and then flush try { Thread.sleep(10); } catch (InterruptedException e) { CommitLog.log.warn("GroupCommitService Exception, ", e); } synchronized (this) { this.swapRequests(); } this.doCommit(); CommitLog.log.info(this.getServiceName() + " service end"); } private void doCommit() { synchronized (this.requestsRead) { if (!this.requestsRead.isEmpty()) { for (GroupCommitRequest req : this.requestsRead) { // There may be a message in the next file, so a maximum of // two times the flush boolean flushOK = false; for (int i = 0; i < 2 && !flushOK; i++) { flushOK = CommitLog.this.mappedFileQueue.getFlushedWhere() >= req.getNextOffset(); if (!flushOK) { // 刷盤實現 CommitLog.this.mappedFileQueue.flush(0); } } req.wakeupCustomer(flushOK ? PutMessageStatus.PUT_OK : PutMessageStatus.FLUSH_DISK_TIMEOUT); } long storeTimestamp = CommitLog.this.mappedFileQueue.getStoreTimestamp(); if (storeTimestamp > 0) { CommitLog.this.defaultMessageStore.getStoreCheckpoint().setPhysicMsgTimestamp(storeTimestamp); } this.requestsRead.clear(); } else { // Because of individual messages is set to not sync flush, it // will come to this process CommitLog.this.mappedFileQueue.flush(0); } } } // org.apache.rocketmq.store.MappedFileQueue#flush public boolean flush(final int flushLeastPages) { boolean result = true; MappedFile mappedFile = this.findMappedFileByOffset(this.flushedWhere, this.flushedWhere == 0); if (mappedFile != null) { long tmpTimeStamp = mappedFile.getStoreTimestamp(); int offset = mappedFile.flush(flushLeastPages); long where = mappedFile.getFileFromOffset() + offset; result = where == this.flushedWhere; this.flushedWhere = where; if (0 == flushLeastPages) { this.storeTimestamp = tmpTimeStamp; } } return result; } // org.apache.rocketmq.store.MappedFile#flush /** * @return The current flushed position */ public int flush(final int flushLeastPages) { if (this.isAbleToFlush(flushLeastPages)) { if (this.hold()) { int value = getReadPosition(); try { //We only append data to fileChannel or mappedByteBuffer, never both. if (writeBuffer != null || this.fileChannel.position() != 0) { this.fileChannel.force(false); } else { this.mappedByteBuffer.force(); } } catch (Throwable e) { log.error("Error occurred when force data to disk.", e); } this.flushedPosition.set(value); this.release(); } else { log.warn("in flush, hold failed, flush offset = " + this.flushedPosition.get()); this.flushedPosition.set(getReadPosition()); } } return this.getFlushedPosition(); }
最後，來看看mappedFile 的建立和預熱過程如何：
public MappedFile putRequestAndReturnMappedFile(String nextFilePath, String nextNextFilePath, int fileSize) { int canSubmitRequests = 2; if (this.messageStore.getMessageStoreConfig().isTransientStorePoolEnable()) { if (this.messageStore.getMessageStoreConfig().isFastFailIfNoBufferInStorePool() && BrokerRole.SLAVE != this.messageStore.getMessageStoreConfig().getBrokerRole()) { //if broker is slave, don't fast fail even no buffer in pool canSubmitRequests = this.messageStore.getTransientStorePool().availableBufferNums() - this.requestQueue.size(); } } AllocateRequest nextReq = new AllocateRequest(nextFilePath, fileSize); boolean nextPutOK = this.requestTable.putIfAbsent(nextFilePath, nextReq) == null; if (nextPutOK) { if (canSubmitRequests <= 0) { log.warn("[NOTIFYME]TransientStorePool is not enough, so create mapped file error, " + "RequestQueueSize : {}, StorePoolSize: {}", this.requestQueue.size(), this.messageStore.getTransientStorePool().availableBufferNums()); this.requestTable.remove(nextFilePath); return null; } boolean offerOK = this.requestQueue.offer(nextReq); if (!offerOK) { log.warn("never expected here, add a request to preallocate queue failed"); } canSubmitRequests--; } AllocateRequest nextNextReq = new AllocateRequest(nextNextFilePath, fileSize); // 放入請求表中，會有任務處理 boolean nextNextPutOK = this.requestTable.putIfAbsent(nextNextFilePath, nextNextReq) == null; if (nextNextPutOK) { if (canSubmitRequests <= 0) { log.warn("[NOTIFYME]TransientStorePool is not enough, so skip preallocate mapped file, " + "RequestQueueSize : {}, StorePoolSize: {}", this.requestQueue.size(), this.messageStore.getTransientStorePool().availableBufferNums()); this.requestTable.remove(nextNextFilePath); } else { // 放入mmap處理佇列，後臺任務開始處理 boolean offerOK = this.requestQueue.offer(nextNextReq); if (!offerOK) { log.warn("never expected here, add a request to preallocate queue failed"); } } } if (hasException) { log.warn(this.getServiceName() + " service has exception. so return null"); return null; } AllocateRequest result = this.requestTable.get(nextFilePath); try { if (result != null) { // 同步等待mmap請求處理完成 boolean waitOK = result.getCountDownLatch().await(waitTimeOut, TimeUnit.MILLISECONDS); if (!waitOK) { log.warn("create mmap timeout " + result.getFilePath() + " " + result.getFileSize()); return null; } else { this.requestTable.remove(nextFilePath); return result.getMappedFile(); } } else { log.error("find preallocate mmap failed, this never happen"); } } catch (InterruptedException e) { log.warn(this.getServiceName() + " service has exception. ", e); } return null; } // 任務只幹一件事，處理呼叫mmapOperation public void run() { log.info(this.getServiceName() + " service started"); while (!this.isStopped() && this.mmapOperation()) { } log.info(this.getServiceName() + " service end"); } /** * Only interrupted by the external thread, will return false */ private boolean mmapOperation() { boolean isSuccess = false; AllocateRequest req = null; try { req = this.requestQueue.take(); AllocateRequest expectedRequest = this.requestTable.get(req.getFilePath()); if (null == expectedRequest) { log.warn("this mmap request expired, maybe cause timeout " + req.getFilePath() + " " + req.getFileSize()); return true; } if (expectedRequest != req) { log.warn("never expected here, maybe cause timeout " + req.getFilePath() + " " + req.getFileSize() + ", req:" + req + ", expectedRequest:" + expectedRequest); return true; } if (req.getMappedFile() == null) { long beginTime = System.currentTimeMillis(); MappedFile mappedFile; if (messageStore.getMessageStoreConfig().isTransientStorePoolEnable()) { try { mappedFile = ServiceLoader.load(MappedFile.class).iterator().next(); // 初始化 mappedFile,實際就是建立commitLog檔案 mappedFile.init(req.getFilePath(), req.getFileSize(), messageStore.getTransientStorePool()); } catch (RuntimeException e) { log.warn("Use default implementation."); mappedFile = new MappedFile(req.getFilePath(), req.getFileSize(), messageStore.getTransientStorePool()); } } else { mappedFile = new MappedFile(req.getFilePath(), req.getFileSize()); } long elapsedTime = UtilAll.computeElapsedTimeMilliseconds(beginTime); if (elapsedTime > 10) { int queueSize = this.requestQueue.size(); log.warn("create mappedFile spent time(ms) " + elapsedTime + " queue size " + queueSize + " " + req.getFilePath() + " " + req.getFileSize()); } // pre write mappedFile if (mappedFile.getFileSize() >= this.messageStore.getMessageStoreConfig() .getMappedFileSizeCommitLog() && this.messageStore.getMessageStoreConfig().isWarmMapedFileEnable()) { mappedFile.warmMappedFile(this.messageStore.getMessageStoreConfig().getFlushDiskType(), this.messageStore.getMessageStoreConfig().getFlushLeastPagesWhenWarmMapedFile()); } req.setMappedFile(mappedFile); this.hasException = false; isSuccess = true; } } catch (InterruptedException e) { log.warn(this.getServiceName() + " interrupted, possibly by shutdown."); this.hasException = true; return false; } catch (IOException e) { log.warn(this.getServiceName() + " service has exception. ", e); this.hasException = true; if (null != req) { requestQueue.offer(req); try { Thread.sleep(1); } catch (InterruptedException ignored) { } } } finally { if (req != null && isSuccess) req.getCountDownLatch().countDown(); } return true; } // store.MappedFile.init() public void init(final String fileName, final int fileSize, final TransientStorePool transientStorePool) throws IOException { init(fileName, fileSize); this.writeBuffer = transientStorePool.borrowBuffer(); this.transientStorePool = transientStorePool; } private void init(final String fileName, final int fileSize) throws IOException { this.fileName = fileName; this.fileSize = fileSize; this.file = new File(fileName); this.fileFromOffset = Long.parseLong(this.file.getName()); boolean ok = false; ensureDirOK(this.file.getParent()); try { // 最核心的建立mmap的地方 // 建立 fileChannel // 建立 mappedByteBuffer, 後續直接使用 this.fileChannel = new RandomAccessFile(this.file, "rw").getChannel(); this.mappedByteBuffer = this.fileChannel.map(MapMode.READ_WRITE, 0, fileSize); TOTAL_MAPPED_VIRTUAL_MEMORY.addAndGet(fileSize); TOTAL_MAPPED_FILES.incrementAndGet(); ok = true; } catch (FileNotFoundException e) { log.error("Failed to create file " + this.fileName, e); throw e; } catch (IOException e) { log.error("Failed to map file " + this.fileName, e); throw e; } finally { if (!ok && this.fileChannel != null) { this.fileChannel.close(); } } }
mappedFile 預熱：
// org.apache.rocketmq.store.MappedFile#warmMappedFile public void warmMappedFile(FlushDiskType type, int pages) { long beginTime = System.currentTimeMillis(); ByteBuffer byteBuffer = this.mappedByteBuffer.slice(); int flush = 0; long time = System.currentTimeMillis(); for (int i = 0, j = 0; i < this.fileSize; i += MappedFile.OS_PAGE_SIZE, j++) { byteBuffer.put(i, (byte) 0); // force flush when flush disk type is sync if (type == FlushDiskType.SYNC_FLUSH) { if ((i / OS_PAGE_SIZE) - (flush / OS_PAGE_SIZE) >= pages) { flush = i; mappedByteBuffer.force(); } } // prevent gc if (j % 1000 == 0) { log.info("j={}, costTime={}", j, System.currentTimeMillis() - time); time = System.currentTimeMillis(); try { Thread.sleep(0); } catch (InterruptedException e) { log.error("Interrupted", e); } } } // force flush when prepare load finished if (type == FlushDiskType.SYNC_FLUSH) { log.info("mapped file warm-up done, force to disk, mappedFile={}, costTime={}", this.getFileName(), System.currentTimeMillis() - beginTime); mappedByteBuffer.force(); } log.info("mapped file warm-up done. mappedFile={}, costTime={}", this.getFileName(), System.currentTimeMillis() - beginTime); this.mlock(); }
如此，整個rocketmq對mappedfile的使用過程就釐清了。
5. mappedFile壓測效能幾何
到底使用mappedFile 之後，效能提升了多少呢？以便衡量收益如何。使用jmh 壓測下。
@State(Scope.Benchmark) public class MmapFileBenchmarkTest { public static void main(String[] args) throws RunnerException { Options opt = new OptionsBuilder() .include(MmapFileBenchmarkTest.class.getSimpleName()) // .include(BenchMarkUsage.class.getSimpleName()+".*measureThroughput*") // 預熱3輪 .warmupIterations(3) // 度量5輪 .measurementIterations(5) .forks(1) .build(); new Runner(opt).run(); } private FileChannel fileChannel; private MappedByteBuffer mappedByteBuffer; private OutputStream outputStream; private int maxWriteLines = 100_0000; private int fileSize = 102400000; @Setup @Before public void setup() throws IOException { File file1 = new File("/tmp/t_mappedFileTest.txt"); this.fileChannel = new RandomAccessFile(file1, "rw").getChannel(); this.mappedByteBuffer = this.fileChannel.map(FileChannel.MapMode.READ_WRITE, 0, 1024000000); // 忽略預熱 // warmMappedFile(); outputStream = FileUtils.openOutputStream(new File("/tmp/t_normalFileTest.txt")); } private void warmMappedFile() { long beginTime = System.currentTimeMillis(); ByteBuffer byteBuffer = this.mappedByteBuffer.slice(); int flush = 0; long time = System.currentTimeMillis(); for (int i = 0, j = 0; i < this.fileSize; i += 4096, j++) { byteBuffer.put(i, (byte) 0); // prevent gc if (j % 1000 == 0) { logInfo("j=%s, costTime=%d", j, System.currentTimeMillis() - time); time = System.currentTimeMillis(); try { Thread.sleep(0); } catch (InterruptedException e) { logInfo("Interrupted, %s", e); } } } // force flush when prepare load finished mappedByteBuffer.force(); // this.mlock(); } private void logInfo(String message, Object... args) { System.out.println(String.format(message, args)); } @Benchmark @BenchmarkMode(Mode.Throughput) @OutputTimeUnit(TimeUnit.SECONDS) @Test public void testAppendMappedFile() throws IOException { for (int i = 0; i < maxWriteLines; i++ ) { mappedByteBuffer.put("abc1234567\n".getBytes()); } mappedByteBuffer.flip(); } @Benchmark @BenchmarkMode(Mode.Throughput) @OutputTimeUnit(TimeUnit.SECONDS) @Test public void testAppendNormalFile() throws IOException { for (int i = 0; i < maxWriteLines; i++ ) { outputStream.write("abc1234567\n".getBytes()); } outputStream.flush(); } }
測試結果如下：
# Run progress: 0.00% complete, ETA 00:00:16 # Fork: 1 of 1 # Warmup Iteration 1: 14.808 ops/s # Warmup Iteration 2: 16.170 ops/s # Warmup Iteration 3: 18.633 ops/s Iteration 1: 15.692 ops/s Iteration 2: 17.273 ops/s Iteration 3: 18.145 ops/s Iteration 4: 18.356 ops/s Iteration 5: 18.868 ops/s Result "MmapFileBenchmarkTest.testAppendMappedFile": 17.667 ±(99.9%) 4.795 ops/s [Average] (min, avg, max) = (15.692, 17.667, 18.868), stdev = 1.245 CI (99.9%): [12.871, 22.462] (assumes normal distribution) # JMH version: 1.19 # VM version: JDK 1.8.0_121, VM 25.121-b13 # Warmup: 3 iterations, 1 s each # Measurement: 5 iterations, 1 s each # Timeout: 10 min per iteration # Threads: 1 thread, will synchronize iterations # Benchmark mode: Throughput, ops/time # Benchmark: MmapFileBenchmarkTest.testAppendNormalFile # Run progress: 50.00% complete, ETA 00:00:09 # Fork: 1 of 1 # Warmup Iteration 1: 0.443 ops/s # Warmup Iteration 2: 0.456 ops/s # Warmup Iteration 3: 0.438 ops/s Iteration 1: 0.406 ops/s Iteration 2: 0.430 ops/s Iteration 3: 0.408 ops/s Iteration 4: 0.399 ops/s Iteration 5: 0.410 ops/s Result "MmapFileBenchmarkTest.testAppendNormalFile": 0.411 ±(99.9%) 0.044 ops/s [Average] (min, avg, max) = (0.399, 0.411, 0.430), stdev = 0.011 CI (99.9%): [0.367, 0.454] (assumes normal distribution) # Run complete. Total time: 00:00:29 Benchmark Mode Cnt Score Error Units MmapFileBenchmarkTest.testAppendMappedFile thrpt 5 17.667 ± 4.795 ops/s MmapFileBenchmarkTest.testAppendNormalFile thrpt 5 0.411 ± 0.044 ops/s
很明顯，mmap厲害些！結論粗糙，僅供參考！