再说rocketmq消息存储

两篇精彩的文章：

《RocketMQ源码 — 三、 Producer消息发送过程》

《RocketMQ源码解析：Message存储》

rocketmq通过netty获取到消息请求后，直接掉处理模块，比如：SendMessageProcessor

这个处理类主要负责处理客户端发送消息的请求。

这个类实现了com.alibaba.rocketmq.remoting.netty.NettyRequestProcessor接口。这个接口下一共两个方法：

RemotingCommand processRequest(ChannelHandlerContext ctx, RemotingCommand request)
        throws Exception;
boolean rejectRequest();

加粗的方法是我们接下来要讲的方法。

它同时还继承了com.alibaba.rocketmq.broker.processor.AbstractSendMessageProcessor。

我们先看一下这个过程的调用链：

这里有一篇博客写的特别好：http://www.cnblogs.com/sunshine-2015/p/6291116.html

再次基础之上补充一点点东西。

首先进入SendMessageProcessor类的第一个方法是：

这个类什么时候被调用的呢？肯定是netty通信模块接收到消息后调用了，具体实在这里：

就是箭头所指的地方调用的上面那个方法。

我们看一下完整的从netty通信模块接收消息到这里的整个过程：

现在就到了我们非常熟悉的Handler了。

这里从下往上看会更加的直观。

好了，我们接着往消息存储走。

我们进入这个方法：

    private RemotingCommand sendMessage(final ChannelHandlerContext ctx, //
                                        final RemotingCommand request, //
                                        final SendMessageContext sendMessageContext, //
                                        final SendMessageRequestHeader requestHeader) throws RemotingCommandException {

        final RemotingCommand response = RemotingCommand.createResponseCommand(SendMessageResponseHeader.class);
        final SendMessageResponseHeader responseHeader = (SendMessageResponseHeader) response.readCustomHeader();

        response.setOpaque(request.getOpaque());

        response.addExtField(MessageConst.PROPERTY_MSG_REGION,this.brokerController.getBrokerConfig().getRegionId());

        if (log.isDebugEnabled()) {
            log.debug("receive SendMessage request command, " + request);
        }

        final long startTimstamp = this.brokerController.getBrokerConfig().getStartAcceptSendRequestTimeStamp();
        if (this.brokerController.getMessageStore().now() < startTimstamp) {
            response.setCode(ResponseCode.SYSTEM_ERROR);
            response.setRemark(String.format("broker unable to service, until %s", UtilAll.timeMillisToHumanString2(startTimstamp)));
            return response;
        }

        response.setCode(-1);
        super.msgCheck(ctx, requestHeader, response);
        if (response.getCode() != -1) {
            return response;
        }

        final byte[] body = request.getBody();

        int queueIdInt = requestHeader.getQueueId();
        TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());

        if (queueIdInt < 0) {
            queueIdInt = Math.abs(this.random.nextInt() % 99999999) % topicConfig.getWriteQueueNums();
        }

        int sysFlag = requestHeader.getSysFlag();

        if (TopicFilterType.MULTI_TAG == topicConfig.getTopicFilterType()) {
            sysFlag |= MessageSysFlag.MultiTagsFlag;
        }

        String newTopic = requestHeader.getTopic();
        if ((null != newTopic && newTopic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX))) {

            String groupName = newTopic.substring(MixAll.RETRY_GROUP_TOPIC_PREFIX.length());

            SubscriptionGroupConfig subscriptionGroupConfig =
                    this.brokerController.getSubscriptionGroupManager().findSubscriptionGroupConfig(groupName);
            if (null == subscriptionGroupConfig) {
                response.setCode(ResponseCode.SUBSCRIPTION_GROUP_NOT_EXIST);
                response.setRemark(
                        "subscription group not exist, " + groupName + " " + FAQUrl.suggestTodo(FAQUrl.SUBSCRIPTION_GROUP_NOT_EXIST));
                return response;
            }

            int maxReconsumeTimes = subscriptionGroupConfig.getRetryMaxTimes();
            if (request.getVersion() >= MQVersion.Version.V3_4_9.ordinal()) {
                maxReconsumeTimes = requestHeader.getMaxReconsumeTimes();
            }
            int reconsumeTimes = requestHeader.getReconsumeTimes();
            if (reconsumeTimes >= maxReconsumeTimes) {
                newTopic = MixAll.getDLQTopic(groupName);
                queueIdInt = Math.abs(this.random.nextInt() % 99999999) % DLQ_NUMS_PER_GROUP;
                topicConfig = this.brokerController.getTopicConfigManager().createTopicInSendMessageBackMethod(newTopic, //
                        DLQ_NUMS_PER_GROUP, //
                        PermName.PERM_WRITE, 0
                );
                if (null == topicConfig) {
                    response.setCode(ResponseCode.SYSTEM_ERROR);
                    response.setRemark("topic[" + newTopic + "] not exist");
                    return response;
                }
            }
        }
        MessageExtBrokerInner msgInner = new MessageExtBrokerInner();
        msgInner.setTopic(newTopic);
        msgInner.setBody(body);
        msgInner.setFlag(requestHeader.getFlag());
        MessageAccessor.setProperties(msgInner, MessageDecoder.string2messageProperties(requestHeader.getProperties()));
        msgInner.setPropertiesString(requestHeader.getProperties());
        msgInner.setTagsCode(MessageExtBrokerInner.tagsString2tagsCode(topicConfig.getTopicFilterType(), msgInner.getTags()));

        msgInner.setQueueId(queueIdInt);
        msgInner.setSysFlag(sysFlag);
        msgInner.setBornTimestamp(requestHeader.getBornTimestamp());
        msgInner.setBornHost(ctx.channel().remoteAddress());
        msgInner.setStoreHost(this.getStoreHost());
        msgInner.setReconsumeTimes(requestHeader.getReconsumeTimes() == null ? 0 : requestHeader.getReconsumeTimes());

        if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) {
            String traFlag = msgInner.getProperty(MessageConst.PROPERTY_TRANSACTION_PREPARED);
            if (traFlag != null) {
                response.setCode(ResponseCode.NO_PERMISSION);
                response.setRemark(
                        "the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1() + "] sending transaction message is forbidden");
                return response;
            }
        }
　　　　 // 前面是一些系统检查和数据准备，下面进入消息存储环节。
        PutMessageResult putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);
        
　　　　　// 锚点putMessage
　　　　　if (putMessageResult != null) {
            boolean sendOK = false;

            switch (putMessageResult.getPutMessageStatus()) {
                // Success
                case PUT_OK:
                    sendOK = true;
                    response.setCode(ResponseCode.SUCCESS);
                    break;
                case FLUSH_DISK_TIMEOUT:
                    response.setCode(ResponseCode.FLUSH_DISK_TIMEOUT);
                    sendOK = true;
                    break;
                case FLUSH_SLAVE_TIMEOUT:
                    response.setCode(ResponseCode.FLUSH_SLAVE_TIMEOUT);
                    sendOK = true;
                    break;
                case SLAVE_NOT_AVAILABLE:
                    response.setCode(ResponseCode.SLAVE_NOT_AVAILABLE);
                    sendOK = true;
                    break;

                // Failed
                case CREATE_MAPEDFILE_FAILED:
                    response.setCode(ResponseCode.SYSTEM_ERROR);
                    response.setRemark("create maped file failed, please make sure OS and JDK both 64bit.");
                    break;
                case MESSAGE_ILLEGAL:
                case PROPERTIES_SIZE_EXCEEDED:
                    response.setCode(ResponseCode.MESSAGE_ILLEGAL);
                    response.setRemark(
                            "the message is illegal, maybe msg body or properties length not matched. msg body length limit 128k, msg properties length limit 32k.");
                    break;
                case SERVICE_NOT_AVAILABLE:
                    response.setCode(ResponseCode.SERVICE_NOT_AVAILABLE);
                    response.setRemark(
                            "service not available now, maybe disk full, " + diskUtil() + ", maybe your broker machine memory too small.");
                    break;
                case OS_PAGECACHE_BUSY:
                    response.setCode(ResponseCode.SYSTEM_ERROR);
                    response.setRemark("[PC_SYNCHRONIZED]broker busy, start flow control for a while");
                    break;
                case UNKNOWN_ERROR:
                    response.setCode(ResponseCode.SYSTEM_ERROR);
                    response.setRemark("UNKNOWN_ERROR");
                    break;
                default:
                    response.setCode(ResponseCode.SYSTEM_ERROR);
                    response.setRemark("UNKNOWN_ERROR DEFAULT");
                    break;
            }

            String owner = request.getExtFields().get(BrokerStatsManager.COMMERCIAL_OWNER);
            if (sendOK) {

                this.brokerController.getBrokerStatsManager().incTopicPutNums(msgInner.getTopic());
                this.brokerController.getBrokerStatsManager().incTopicPutSize(msgInner.getTopic(),
                        putMessageResult.getAppendMessageResult().getWroteBytes());
                this.brokerController.getBrokerStatsManager().incBrokerPutNums();

                response.setRemark(null);

                responseHeader.setMsgId(putMessageResult.getAppendMessageResult().getMsgId());
                responseHeader.setQueueId(queueIdInt);
                responseHeader.setQueueOffset(putMessageResult.getAppendMessageResult().getLogicsOffset());

                doResponse(ctx, request, response);

                if (hasSendMessageHook()) {
                    sendMessageContext.setMsgId(responseHeader.getMsgId());
                    sendMessageContext.setQueueId(responseHeader.getQueueId());
                    sendMessageContext.setQueueOffset(responseHeader.getQueueOffset());

                    int wroteSize = putMessageResult.getAppendMessageResult().getWroteBytes();
                    int incValue = (int) Math.ceil(wroteSize / BrokerStatsManager.SIZE_PER_COUNT);

                    sendMessageContext.setCommercialSendStats(BrokerStatsManager.StatsType.SEND_SUCCESS);
                    sendMessageContext.setCommercialSendTimes(incValue);
                    sendMessageContext.setCommercialSendSize(wroteSize);
                    sendMessageContext.setCommercialOwner(owner);
                }
                return null;
            } else {
                if (hasSendMessageHook()) {
                    int wroteSize = request.getBody().length;
                    int incValue = (int) Math.ceil(wroteSize / BrokerStatsManager.SIZE_PER_COUNT);

                    sendMessageContext.setCommercialSendStats(BrokerStatsManager.StatsType.SEND_FAILURE);
                    sendMessageContext.setCommercialSendTimes(incValue);
                    sendMessageContext.setCommercialSendSize(wroteSize);
                    sendMessageContext.setCommercialOwner(owner);
                }
            }
        } else {
            response.setCode(ResponseCode.SYSTEM_ERROR);
            response.setRemark("store putMessage return null");
        }

        return response;
    }

我们进入PutMessageResult putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);

的MessageStore.putMessage(msgInner)方法。

MesageStore这个接口一共有三个实现类：

实现了上面那个方法的只有DefaultMessageStore实现类。所以我们看DefaultMessageStore.putMessage(MessageExtBrokerInner msg)方法。

    public PutMessageResult putMessage(MessageExtBrokerInner msg) {
        if (this.shutdown) {
            log.warn("message store has shutdown, so putMessage is forbidden");
            return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
        }

        if (BrokerRole.SLAVE == this.messageStoreConfig.getBrokerRole()) {
            long value = this.printTimes.getAndIncrement();
            if ((value % 50000) == 0) {
                log.warn("message store is slave mode, so putMessage is forbidden ");
            }

            return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
        }

        if (!this.runningFlags.isWriteable()) {
            long value = this.printTimes.getAndIncrement();
            if ((value % 50000) == 0) {
                log.warn("message store is not writeable, so putMessage is forbidden " + this.runningFlags.getFlagBits());
            }

            return new PutMessageResult(PutMessageStatus.SERVICE_NOT_AVAILABLE, null);
        } else {
            this.printTimes.set(0);
        }

        // message topic长度校验
        if (msg.getTopic().length() > Byte.MAX_VALUE) {
            log.warn("putMessage message topic length too long " + msg.getTopic().length());
            return new PutMessageResult(PutMessageStatus.MESSAGE_ILLEGAL, null);
        }

        // message properties长度校验
        if (msg.getPropertiesString() != null && msg.getPropertiesString().length() > Short.MAX_VALUE) {
            log.warn("putMessage message properties length too long " + msg.getPropertiesString().length());
            return new PutMessageResult(PutMessageStatus.PROPERTIES_SIZE_EXCEEDED, null);
        }

        if (this.isOSPageCacheBusy()) {
            return new PutMessageResult(PutMessageStatus.OS_PAGECACHE_BUSY, null);
        }

        long beginTime = this.getSystemClock().now();
　　　　 //上面是一些系统检查，下面是消息的存储
        PutMessageResult result = this.commitLog.putMessage(msg);
        // 性能数据统计
        long eclipseTime = this.getSystemClock().now() - beginTime;
        if (eclipseTime > 1000) {
            log.warn("putMessage not in lock eclipse time(ms)={}, bodyLength={}", eclipseTime, msg.getBody().length);
        }
        this.storeStatsService.setPutMessageEntireTimeMax(eclipseTime);

        if (null == result || !result.isOk()) {
            this.storeStatsService.getPutMessageFailedTimes().incrementAndGet();
        }

        return result;
    }

其中commitLog在构造方法中的初始化：this.commitLog = new CommitLog(this);

我们接着进入commitLog.putMessage(final MessageExtBrokerInner msg)

这个方法搞定了，你也就彻底了解了rocketmq的消息存储过程了。

    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.TransactionNotType//
                || tranType == MessageSysFlag.TransactionCommitType) {
            // Delay Delivery
            if (msg.getDelayTimeLevel() > 0) {
                if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) {
                    msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel());
                }

                topic = ScheduleMessageService.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 eclipseTimeInLock = 0;
        MapedFile unlockMapedFile = null;
        MapedFile mapedFile = this.mapedFileQueue.getLastMapedFileWithLock();
        synchronized (this) {
            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 == mapedFile || mapedFile.isFull()) {
                mapedFile = this.mapedFileQueue.getLastMapedFile();
            }
            if (null == mapedFile) {
                log.error("create maped file1 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
                beginTimeInLock = 0;
                return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, null);
            }
            result = mapedFile.appendMessage(msg, this.appendMessageCallback);
            switch (result.getStatus()) {
                case PUT_OK:
                    break;
                case END_OF_FILE:
                    unlockMapedFile = mapedFile;
                    // Create a new file, re-write the message
                    mapedFile = this.mapedFileQueue.getLastMapedFile();
                    if (null == mapedFile) {
                        // XXX: warn and notify me
                        log.error("create maped file2 error, topic: " + msg.getTopic() + " clientAddr: " + msg.getBornHostString());
                        beginTimeInLock = 0;
                        return new PutMessageResult(PutMessageStatus.CREATE_MAPEDFILE_FAILED, result);
                    }
                    result = mapedFile.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);
            }

            eclipseTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp;
            beginTimeInLock = 0;
        } // end of synchronized

        if (eclipseTimeInLock > 1000) {
            log.warn("[NOTIFYME]putMessage in lock cost time(ms)={}, bodyLength={} AppendMessageResult={}", eclipseTimeInLock, msg.getBody().length, result);
        }
        if (null != unlockMapedFile) {
            this.defaultMessageStore.unlockMapedFile(unlockMapedFile);
        }

        PutMessageResult putMessageResult = new PutMessageResult(PutMessageStatus.PUT_OK, result);

        // Statistics
        storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).incrementAndGet();
        storeStatsService.getSinglePutMessageTopicSizeTotal(topic).addAndGet(result.getWroteBytes());

        GroupCommitRequest request = null;

        // Synchronization flush
        if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) {
            GroupCommitService service = (GroupCommitService) this.flushCommitLogService;
            if (msg.isWaitStoreMsgOK()) {
                request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());
                service.putRequest(request);
                boolean flushOK = request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
                if (!flushOK) {
                    log.error("do groupcommit, wait for flush failed, topic: " + msg.getTopic() + " tags: " + msg.getTags()
                            + " client address: " + msg.getBornHostString());
                    putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT);
                }
            } else {
                service.wakeup();
            }
        }
        // Asynchronous flush
        else {
            this.flushCommitLogService.wakeup();
        }

        // Synchronous write double
        if (BrokerRole.SYNC_MASTER == this.defaultMessageStore.getMessageStoreConfig().getBrokerRole()) {
            HAService service = this.defaultMessageStore.getHaService();
            if (msg.isWaitStoreMsgOK()) {
                // Determine whether to wait
                if (service.isSlaveOK(result.getWroteOffset() + result.getWroteBytes())) {
                    if (null == request) {
                        request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());
                    }
                    service.putRequest(request);

                    service.getWaitNotifyObject().wakeupAll();

                    boolean flushOK =
                            // TODO
                            request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
                    if (!flushOK) {
                        log.error("do sync transfer other node, wait return, but failed, topic: " + msg.getTopic() + " tags: "
                                + msg.getTags() + " client address: " + msg.getBornHostString());
                        putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_SLAVE_TIMEOUT);
                    }
                }
                // Slave problem
                else {
                    // Tell the producer, slave not available
                    putMessageResult.setPutMessageStatus(PutMessageStatus.SLAVE_NOT_AVAILABLE);
                }
            }
        }

        return putMessageResult;
    }

我们进入标黄的方法：

/**
     * 插入消息到 MappedFile，并返回插入结果。
     * MappedFile的理解就可以按照字面意思来理解。换一种说法就是file的缓冲区。刷盘之前先写入缓存区。nio就是这样的。
     * @param msg
     * @param cb
     * @return
     */
    public AppendMessageResult appendMessage(final Object msg, final AppendMessageCallback cb) {
        assert msg != null;
        assert cb != null;

        int currentPos = this.wrotePostion.get();

        if (currentPos < this.fileSize) {
            // 获取需要写入的字节缓冲区。为什么会有 writeBuffer != null 的判断后，使用不同的字节缓冲区，见：FlushCommitLogService。
            ByteBuffer byteBuffer = this.mappedByteBuffer.slice();
            byteBuffer.position(currentPos);
            AppendMessageResult result =
                    cb.doAppend(this.getFileFromOffset(), byteBuffer, this.fileSize - currentPos, msg);
            this.wrotePostion.addAndGet(result.getWroteBytes());
            this.storeTimestamp = result.getStoreTimestamp();
            return result;
        }

        log.error("MapedFile.appendMessage return null, wrotePostion: " + currentPos + " fileSize: "
                + this.fileSize);
        return new AppendMessageResult(AppendMessageStatus.UNKNOWN_ERROR);
    }

接着看上面这个标黄的方法：

       public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank, final Object msg) {
            // STORETIMESTAMP + STOREHOSTADDRESS + OFFSET <br>
            MessageExtBrokerInner msgInner = (MessageExtBrokerInner) msg;
            // PHY OFFSET
            long wroteOffset = fileFromOffset + byteBuffer.position();

            String msgId = MessageDecoder.createMessageId(this.msgIdMemory, msgInner.getStoreHostBytes(), wroteOffset);

            // Record ConsumeQueue information
            String key = msgInner.getTopic() + "-" + msgInner.getQueueId();
            Long queueOffset = CommitLog.this.topicQueueTable.get(key);
            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.TransactionPreparedType:
                case MessageSysFlag.TransactionRollbackType:
                    queueOffset = 0L;
                    break;
                case MessageSysFlag.TransactionNotType:
                case MessageSysFlag.TransactionCommitType:
                default:
                    break;
            }

            /**
             * Serialize message 序列化消息
             */
            final byte[] propertiesData =
                    msgInner.getPropertiesString() == null ? null : msgInner.getPropertiesString().getBytes(MessageDecoder.CHARSET_UTF8);
            if (propertiesData.length > Short.MAX_VALUE) {
                log.warn("putMessage message properties length too long. length={}", propertiesData.length);
                return new AppendMessageResult(AppendMessageStatus.PROPERTIES_SIZE_EXCEEDED);
            }

            final short propertiesLength = propertiesData == null ? 0 : (short) propertiesData.length;

            final byte[] topicData = msgInner.getTopic().getBytes(MessageDecoder.CHARSET_UTF8);
            final int topicLength = topicData == null ? 0 : topicData.length;

            final int bodyLength = msgInner.getBody() == null ? 0 : msgInner.getBody().length;

            final int msgLen = calMsgLength(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
            // 确定是否有足够的空间
            if ((msgLen + END_FILE_MIN_BLANK_LENGTH) > maxBlank) {
                this.resetMsgStoreItemMemory(maxBlank);
                // 1 TOTALSIZE
                this.msgStoreItemMemory.putInt(maxBlank);
                // 2 MAGICCODE
                this.msgStoreItemMemory.putInt(CommitLog.BlankMagicCode);
                // 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);
            }

            // Initialization of storage space
            this.resetMsgStoreItemMemory(msgLen);
            // 1 TOTALSIZE
            this.msgStoreItemMemory.putInt(msgLen);
            // 2 MAGICCODE
            this.msgStoreItemMemory.putInt(CommitLog.MessageMagicCode);
            // 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.msgStoreItemMemory.put(msgInner.getBornHostBytes());
            // 11 STORETIMESTAMP
            this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp());
            // 12 STOREHOSTADDRESS
            this.msgStoreItemMemory.put(msgInner.getStoreHostBytes());
            // 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(propertiesLength);
            if (propertiesLength > 0)
                this.msgStoreItemMemory.put(propertiesData);

            final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
            // message:>>>>>>>:Hello RocketMQ 0
            System.out.println("message:>>>>>>>:" + new String(msgInner.getBody()));
            // Write messages to the queue buffer
            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.TransactionPreparedType:
                case MessageSysFlag.TransactionRollbackType:
                    break;
                case MessageSysFlag.TransactionNotType:
                case MessageSysFlag.TransactionCommitType:
                    // The next update ConsumeQueue information
                    CommitLog.this.topicQueueTable.put(key, ++queueOffset);
                    break;
                default:
                    break;
            }

            return result;
        }

        private void resetMsgStoreItemMemory(final int length) {
            this.msgStoreItemMemory.flip();
            this.msgStoreItemMemory.limit(length);
        }
    }

我们注意到消息被保存到了：msgStoreItemMemory这里，这是一个内存映射文件MappedByteBuffer

可以参考（http://www.cnblogs.com/guazi/p/6829487.html）

他声明在MapedFile中，这个类我们上面说了，他的功能和他的名字正好相符。

//映射的内存对象 文件映射为的内存
private final MappedByteBuffer mappedByteBuffer;

//映射的FileChannel对象 nio阻塞
private FileChannel fileChannel;

在构造方法中初始化：

this.fileChannel = new RandomAccessFile(this.file, "rw").getChannel();
this.mappedByteBuffer = this.fileChannel.map(MapMode.READ_WRITE, 0, fileSize);

保存到这里之后，我们回到最开始的 sendMessage方法中的锚点

消息保存的映射缓存中后，就启动耍盘线程了，同样是在sendmessage方法中，接下来就是耍盘操作了：

...
    ...
　　　　 // 消息刷盘，即持久化到文件。上面插入消息实际未存储到硬盘。此处，根据不同的刷盘策略，执行会有不同。详细解析见：FlushCommitLogService。
        // 进行同步||异步 flush||commit
        GroupCommitRequest request = null;

        // Synchronization flush
        if (FlushDiskType.SYNC_FLUSH == this.defaultMessageStore.getMessageStoreConfig().getFlushDiskType()) {
            GroupCommitService service = (GroupCommitService) this.flushCommitLogService;
            if (msg.isWaitStoreMsgOK()) {
                request = new GroupCommitRequest(result.getWroteOffset() + result.getWroteBytes());
                service.putRequest(request);
                boolean flushOK = request.waitForFlush(this.defaultMessageStore.getMessageStoreConfig().getSyncFlushTimeout());
                if (!flushOK) {
                    log.error("do groupcommit, wait for flush failed, topic: " + msg.getTopic() + " tags: " + msg.getTags()
                            + " client address: " + msg.getBornHostString());
                    putMessageResult.setPutMessageStatus(PutMessageStatus.FLUSH_DISK_TIMEOUT);
                }
            } else {
                service.wakeup();
            }
        }
        // Asynchronous flush
        else {
            this.flushCommitLogService.wakeup();// important：唤醒commitLog线程，进行flush。具体看flushCommitLogService的实现类
        }
    ...
...

这里分成了种刷盘方式，一种是同步FlushDiskType.SYNC_FLUSH，一种是异步。

配置系统的同步和异步刷盘方式可以通过这里看到：

同步的是这个线程：GroupCommitService service = (GroupCommitService) this.flushCommitLogService;来处理刷盘逻辑。

我们直接看他的刷盘业务代码：

        private void doCommit() {
            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.mapedFileQueue.getCommittedWhere() >= req.getNextOffset());

                        if (!flushOK) {
                            CommitLog.this.mapedFileQueue.commit(0);
                        }
                    }

                    req.wakeupCustomer(flushOK);
                }

                long storeTimestamp = CommitLog.this.mapedFileQueue.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.mapedFileQueue.commit(0);
            }
        }

最后调用：CommitLog.this.mapedFileQueue.commit(0);来保存到硬盘。

　　// 消息文件队列，包含所有保存在磁盘上的文件。另外MappedFile和文件一对一关系。这两个类之间的关系非常紧密。

com.alibaba.rocketmq.store.MapedFileQueue

这个也是在 CommitLog的构造方法中初始化的。

MapedFileQueue mapedFileQueue;

this.mapedFileQueue = new MapedFileQueue(defaultMessageStore.getMessageStoreConfig().getStorePathCommitLog(),
        defaultMessageStore.getMessageStoreConfig().getMapedFileSizeCommitLog(), defaultMessageStore.getAllocateMapedFileService());

　　public MapedFileQueue(final String storePath, int mapedFileSize,
                          AllocateMapedFileService allocateMapedFileService) {
        this.storePath = storePath;
        this.mapedFileSize = mapedFileSize;
        this.allocateMapedFileService = allocateMapedFileService;
    }

看一下commit(final int flushLeastPages)方法：

   public boolean commit(final int flushLeastPages) {
        boolean result = true;
        MapedFile mapedFile = this.findMapedFileByOffset(this.committedWhere, true);
        if (mapedFile != null) {
            long tmpTimeStamp = mapedFile.getStoreTimestamp();
            int offset = mapedFile.commit(flushLeastPages);
            long where = mapedFile.getFileFromOffset() + offset;
            result = (where == this.committedWhere);
            this.committedWhere = where;
            if (0 == flushLeastPages) {
                this.storeTimestamp = tmpTimeStamp;
            }
        }

        return result;
    }

    public MapedFile findMapedFileByOffset(final long offset, final boolean returnFirstOnNotFound) {
        try {
            this.readWriteLock.readLock().lock();
            MapedFile mapedFile = this.getFirstMapedFile();

            if (mapedFile != null) {
                int index =
                        (int) ((offset / this.mapedFileSize) - (mapedFile.getFileFromOffset() / this.mapedFileSize));
                if (index < 0 || index >= this.mapedFiles.size()) {
                    logError
                            .warn(
                                    "findMapedFileByOffset offset not matched, request Offset: {}, index: {}, mapedFileSize: {}, mapedFiles count: {}, StackTrace: {}",//
                                    offset,//
                                    index,//
                                    this.mapedFileSize,//
                                    this.mapedFiles.size(),//
                                    UtilAll.currentStackTrace());
                }

                try {
                    return this.mapedFiles.get(index);
                } catch (Exception e) {
                    if (returnFirstOnNotFound) {
                        return mapedFile;
                    }
                }
            }
        } catch (Exception e) {
            log.error("findMapedFileByOffset Exception", e);
        } finally {
            this.readWriteLock.readLock().unlock();
        }

        return null;
    }

    private MapedFile getFirstMapedFile() {
        if (this.mapedFiles.isEmpty()) {
            return null;
        }

        return this.mapedFiles.get(0);
    }

最终要找到mapedFiles的赋值的方法：

就是他了！！！

   com.alibaba.rocketmq.store.MapedFileQueue

　　public boolean load() {
        File dir = new File(this.storePath);
        File[] files = dir.listFiles();
        if (files != null) {
            // ascending order
            Arrays.sort(files);
            for (File file : files) {

                if (file.length() != this.mapedFileSize) {
                    log.warn(file + "\t" + file.length()
                            + " length not matched message store config value, ignore it");
                    return true;
                }

                try {
                    MapedFile mapedFile = new MapedFile(file.getPath(), mapedFileSize);

                    mapedFile.setWrotePostion(this.mapedFileSize);
                    mapedFile.setCommittedPosition(this.mapedFileSize);
                    this.mapedFiles.add(mapedFile);
                    log.info("load " + file.getPath() + " OK");
                } catch (IOException e) {
                    log.error("load file " + file + " error", e);
                    return false;
                }
            }
        }

        return true;
    }

现在来看看这个MapedFile的构造方法：

需要注意的是一个内部属性：

//文件的起始偏移量 该文件的全局offset，也就是文件名的前缀
private final long fileFromOffset;

    public MapedFile(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 {
            this.fileChannel = new RandomAccessFile(this.file, "rw").getChannel();
　　　　　　　this.mappedByteBuffer = this.fileChannel.map(MapMode.READ_WRITE, 0, fileSize);
            TotalMapedVitualMemory.addAndGet(fileSize);
            TotalMapedFiles.incrementAndGet();
            ok = true;
        } catch (FileNotFoundException e) {
            log.error("create file channel " + this.fileName + " Failed. ", e);
            throw e;
        } catch (IOException e) {
            log.error("map file " + this.fileName + " Failed. ", e);
            throw e;
        } finally {
            if (!ok && this.fileChannel != null) {
                this.fileChannel.close();
            }
        }
    }

好了回到。

int offset = mapedFile.commit(flushLeastPages)；

接着看：

    /**
     * 消息刷盘
     *
     * @param flushLeastPages
     *            至少刷几个page
     *
     * @return
     */
    public int commit(final int flushLeastPages) {
        //判断当前是否能刷盘
        if (this.isAbleToFlush(flushLeastPages)) {
            //类似于一个智能指针，控制刷盘线程数
            if (this.hold()) {
                int value = this.wrotePostion.get();
                //刷盘，内存到硬盘
                this.mappedByteBuffer.force();
                this.committedPosition.set(value);
                //释放智能指针
                this.release();
            } else {
                log.warn("in commit, hold failed, commit offset = " + this.committedPosition.get());
                this.committedPosition.set(this.wrotePostion.get());
            }
        }

        return this.getCommittedPosition();
    }

到这来说刷盘就算结束了。当然中间跳过了很多，也是不得已的事，争取再抽时间把文章拆分一下。