RocketMQ作为消息中间件，经常会被用来和其他消息中间件做比较，比对rabbitmq, kafka... 但个人觉得它一直对标的，都是kafka。因为它们面对的场景往往都是超高并发，超高性能要求的场景。
所以，有必要深挖下其实现高性能，高并发的原因。实际上，这是非常大的话题，我这里也不打算一口吃个大胖子。我会给出个大概答案，然后我们再深入挖掘其中部分实现。如题所述。
1. 高性能高并发系统的底层技能概述
我不打算单讲rocketmq到底是如何实现高性能高并发的，因为实际上的底层原则都是差不多的。rocketmq不过是其中的一个实现者而已。
那么，要想实现高性能高并发，大概需要怎么做的呢？本质上讲，我们的系统服务能利用的东西并不多，CPU、内存、磁盘、网络、硬件特性。。。 当然了，还有一个非常重要的东西，就是我们基本都是在做应用层服务，所以我们的能力往往必须依托于操作系统提供的服务，由这些服务去更好地利用底层硬件的东西。好吧，显得逼格好像有点高了，实际上就是一个系统API调用。
接下来，我们从每个小点出发，来看看我们如何做到高性能高并发：
第一个：CPU。可以说，CPU代表了单机的极限。如果能够做有效利用CPU, 使其随时可保证在80%以上的使用率，那么你这个服务绝对够牛逼了（注意不是导致疯狂GC的那种利用率哦）。那么，我们如何做到高效利用CPU呢？有些应用天然就是CPU型的，比如提供一些做大数的运算服务，天生就需要大量CPU运算。而其他的很多的IO型的应用，则CPU往往不会太高，或者说我们应该往高了的方向优化。
第二个：内存。内存是一个非常宝贵的资源，因为内存的调度速度非常快。如果一个应用的业务处理都是基于内存的，那么这个应用基本上就会超级强悍。大部分情况下，越大的内存往往也能提供越高的性能，比如ES的搜索服务，要想性能好必需有足够内存。当然了，内存除了使用起来非常方便之外，它还有一个重要的工作，就是内存的回收。当然，这部分工作一般都会被编程语言屏蔽掉，因为它实在太难了。我们一般只需按照语言特性，合理的处理对象即可。另外，我们可以使一些可能需要从外部设备读入的数据，加载到内存中长期使用，这将是一件非常重要的优化动作。如何维护好数据一致性与安全性和准确性，是这类工作的重点。
第三个：磁盘。内存虽好，但却不常有。内存往往意味着大小受限。而与之对应的就是磁盘，磁盘则往往意味空间非常大，数据永久存储安全。磁盘基本上就代表了单机的存储极限，但也同时限制了并发能力。
第四个：网络。也许这个名词不太合适，但却是因为网络才发生了变化。如果说前面讲的都是单机的极限性能，那么，网络就会带来分布式系统的极限性能。一个庞大的系统，一定是分布式的，因此必然会使用到网络这个设备。但我们一般不会在这上面节省多少东西，我们能做的，也许就是简单的压缩下文件数据而已。更多的，也许我们只是申请更大的带宽，或者开辟新的布线，以满足系统的需要。在网络这一环境，如何更好地组织网络设备，是重中之重，而这往往又回到了上面三个话题之一了。
最后，排除上面几个硬技能，还有一个也是非常重要的技能：那就是算法，没有好的算法，再多的优化可能也只是杯水车薪。（当然了我们大部分情况下是无需高级算法的，因为大部分时间，我们只是大自然的搬运工）
2. 高性能高并发操作系统api列举
前面说的，更多是理论上讲如何形成牛逼的应用服务。但我们又没那能力去搞操作系统的东西，所以也只能想想而已。那么说到底，我们能做什么呢？所谓工欲善其事，必先利其器。所谓利器，也就是看看操作系统提供什么样的底层API 。
我这里就稍微列几个吧（我也就知道这么些了）：
epoll系列: IO多路复用技术，高并发高性能网络应用必备。大致作用就是使用极少数的线程，高效地管理大量io事件，通知应用等。大概的接口有: epoll_create(), epoll_ctl(), epoll_wait();
pagecache系列: 操作系统页缓存，高效读写文件必备。大致作用就是保留部分磁盘数据在内存中，以便应用想读取或者磁盘数据数据时能够非常快速的响应。相关接口如: read(), write(), readpage(), writepage(), sync(), fsync().
mmap系列: 内存映射。可以将文件映射到内存中，用户写数据时直接向该内存缓冲区写数据，即可达到写磁盘的作用了，从而提高写入性能。接口如: mmap(), munmap();
directio系列: 直接io操作，避免用户态数据到内核态数据的相互copy, 节省cpu和内存占用。
cas系列: 高效安全锁实现。相关接口: cmpxchg() 。
多线程系列: 大部分网络应用，都io型的，那么如何同时处理多个请求就非常重要了。多线程提供非常便捷的并发编程基础，使得我们可以更简单的处理业务而且提供超高的处理能力。这自然是编程语言直接提供的。
3. rocketmq中的高性能法宝
rocketmq想要实现高并发高性能处理能力，自然要从操作系统层面去寻求方法，自然也就逃不过前面的几点说法了。
首先，它基于netty实现了高性能的网络通信，netty基于事件的io模型，零拷贝的技术，已经提供了非常好的技术前提，rocketmq只需利用一下，就可以将自己变得很厉害了。当然，这只是其厉害的一个点，因为单有了高效网络通信处理能力还不够的。至少，rocketmq得提供高效的数据序列化方式。
其次，有了netty作为通信框架，高效接入请求后，rocketmq自身处理业务的方式非常重要。如果能够直接基于内存保存数据，那必然是最高性能的。但是它不能那样做，因为内存太小，无法容纳下应有的消息。所以，只能基于文件做存储。而文件本身的操作又是代价非常高的，所以，必须要有些稍微的措施，避免重量级的操作文件。所以，文件的多级存储又是非常重要的了，即如索引文件在db中的应用就知道了。
再其次，java提供了非常好的多线程编程环境，不加以利用就对不起观众了。良好的线程模型，为其高性能呐喊助威。
最后，基于pagecache和mmap的高效文件读写，才是其制胜法宝。这也是我们接下来想要重点说明的。
4. rocketmq中对mmap和pagecache的应用
上一点中提到的每个点，都是rocketmq出众的原因，但我们今天只会来说一点：rocketmq的高效文件存储。
实际上，根据我之前的几篇文章，我们很容易找到rocketmq是如何对文件进行读写的。我们就以producer写消息数据为例，来回顾看看rmq是如何进行高效文件存储的。
// 处理器入口 // 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; } // 接收转发，异步处理 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: // 写入数据 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 { // 简单起见，我们只看非事务的消息写入 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)); } // 写入消息数据到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; } // 写入消息数据到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; // 获取mappedFile实例，后续将向其写入数据 MappedFile unlockMappedFile = null; MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile(); // 上锁写数据，保证数据写入安全准确 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); // 确保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中追加数据，完成写入动作 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; }); } // 获取有效的mappedFile实例 // 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; } // 再次尝试获取 mappedFile, 没有则创建一个新的 // 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; // 分配创建一个新的commitLog文件 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顺序写入数据 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) { // 回调，写入数据到 commitLog 中 // 将数据写入 byteBuffer, 即将数据写入了pagecache, 也就写入了磁盘文件中了 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信息 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); } // 序列化写入数据，写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 // 将数据写入 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; }
以上过程看似复杂，实则只有最后一个bytebuffer.putXxx() 是真正的和mappedFile 是相关的。当然了，还有MappedFile的初始过程，它会先尝试从现有打开的mappFiles中获取最后一个实例，如果mappedFile满了之后，就会尝试创建一个新的mappedFile, 这个过程一般伴随着新的commitLog文件的创建。
mappedFile 的刷盘动作，主要分为同步刷盘和异步刷，底层都是一样的，即调用 flush(),MappedFileChannel.force(), 将pagecache强制刷入到磁盘上。一般地，将数据写入pagecache，基本就能保证不丢失了。但还是有例外情况，比如机器掉电，或者系统bug这种极端情况，还是会导致丢数据哟。
下面大致来看看 mappedFile 同步刷盘过程：
// org.apache.rocketmq.store.CommitLog#handleDiskFlush public void handleDiskFlush(AppendMessageResult result, PutMessageResult putMessageResult, MessageExt messageExt) { // Synchronization flush // 同步刷盘 if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) { final GroupCommitService service = (GroupCommitService) this.flushCommitLogService; if (messageExt.isWaitStoreMsgOK()) { // 提交一个刷盘任务到 GroupCommitService, 同步等待结果响应 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 // 异步刷盘 else { // 异步刷盘则直接唤醒一个刷盘线程即可 if (!this.defaultMessageStore.getMessageStoreConfig().isTransientStorePoolEnable()) { flushCommitLogService.wakeup(); } else { commitLogService.wakeup(); } } } // org.apache.rocketmq.store.CommitLog.GroupCommitService#putRequest // 添加刷盘请求 public synchronized void putRequest(final GroupCommitRequest request) { synchronized (this.requestsWrite) { this.requestsWrite.add(request); } this.wakeup(); } // 刷盘线程一直运行 public void run() { CommitLog.log.info(this.getServiceName() + " service started"); while (!this.isStopped()) { try { this.waitForRunning(10); // 运行真正的刷动作 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) { // 刷盘实现 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(); }
最后，来看看mappedFile 的创建和预热过程如何：
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); // 放入请求表中，会有任务处理 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处理队列，后台任务开始处理 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请求处理完成 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; } // 任务只干一件事，处理调用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,实际就是创建commitLog文件 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 { // 最核心的创建mmap的地方 // 创建 fileChannel // 创建 mappedByteBuffer, 后续直接使用 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 预热：
// 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，整个rocketmq对mappedfile的使用过程就厘清了。
5. mappedFile压测性能几何
到底使用mappedFile 之后，性能提升了多少呢？以便衡量收益如何。使用jmh 压测下。
@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*") // 预热3轮 .warmupIterations(3) // 度量5轮 .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); // 忽略预热 // 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 ".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 ".getBytes()); } outputStream.flush(); } }
测试结果如下：
# 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
很明显，mmap厉害些！结论粗糙，仅供参考！