消息队列（五）--- RocketMQ-消息存储1

问题 ；

• 部署时如何知道自己是 broker 还是 NameServer
• topic 订阅信息放在哪里
• broker 的作用到底是什么
• 纪录是如何持久化的
• 群发的时候，是如何储存消息的
• send 方法到底有没有使用多线程发送处理，简单叙述一个 send 的过程
• transientStorePool 作用到底是什么
• 为什么要使用堆外内存来存储消息先，而不是使用堆内内存
  
  以上几个问题，是在学习中思考的问题，我们将在学习过程中逐渐寻找答案。

概述

本文将会走完文件存储的主体流程，后续分析各个重要的类。下面简述来自参考资料，过程简述如下 ：

SendMessageProcessor.processRequest
  -->buildMsgContext(ctx, requestHeader);
  -->this.executeSendMessageHookBefore(ctx, request, mqtraceContext);
  -->sendMessage
    (检查消息)
    -->super.msgCheck(ctx, requestHeader, response);
    (查询topic的配置信息)
    -->this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());
    (处理重试消息)
    -->handleRetryAndDLQ(requestHeader, response, request, msgInner, topicConfig)
    -->this.brokerController.getMessageStore().putMessage(msgInner);
        -->this.commitLog.putMessage(msg);
            -->this.mappedFileQueue.getLastMappedFile();
            -->mappedFile.appendMessage(msg, this.appendMessageCallback);
            (如果是同步刷盘则立即调用该方法刷盘)
            -->handleDiskFlush(result, putMessageResult, msg);
            -->异步刷盘的情况下通过唤起FlushRealTimeService的线程刷盘
            (处理主从同步)
            -->handleHA(result, putMessageResult, messageExtBatch);

源码分析

消息持久化几个重要的类 ：

• DefaultMessageStore
• commitLog
• MappedFile

DefaultMessageStore 持有 commitLog ，commitLog 持有 MappedFileQueue ，MappedFileQueue 管理着多个 MappedFile.

首先我们从 DefaultMessageStore 的 putMessage 方法

    /**
     * 1. 判断是否条件满足条件
     * 2. 调用 this.commitLog.putMessage(msg);
     *
     * @param msg Message instance to store
     * @return
     */
    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);
        }

        // 该 broker 是 slave 模式
        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);
        }

        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);
        }

        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();
        //写入逻辑
        PutMessageResult result = this.commitLog.putMessage(msg);

        long eclipseTime = this.getSystemClock().now() - beginTime;
        if (eclipseTime > 500) {
            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;
    }

CommitLog 的 putMessage 方法

    /**
     * @param msg
     * @return
     */
    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 延迟发送，将topic 换成 SCHEDULE_TOPIC , queueId 换成 延迟时间级别
            // 这是并发消息消费重试关键的一步，下一章会重点探讨消息重试机制与定时消息的实现原理。
            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;
        MappedFile unlockMappedFile = null;
        MappedFile mappedFile = this.mappedFileQueue.getLastMappedFile();

        putMessageLock.lock(); //spin or ReentrantLock ,depending on store config  自旋或是重入锁看存储配置
        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);
            }
            //核心逻辑！！可知 mappedFile是最终写入文件中的实施者
            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);
            }

            eclipseTimeInLock = this.defaultMessageStore.getSystemClock().now() - beginLockTimestamp;
            beginTimeInLock = 0;
        } finally {
            putMessageLock.unlock();
        }

        if (eclipseTimeInLock > 500) {
            log.warn("[NOTIFYME]putMessage in lock cost time(ms)={}, bodyLength={} AppendMessageResult={}", eclipseTimeInLock, 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;
    }

mappedFile 执行写入内存操作

    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();
        // 判断写针位置（是否已经大于文件大小）如果 currentPos 小于文件大小，通过 slice（）方法创建一个与 MappedFile 的共享 内
        //存区，并设置 position 为当前指针 。
        if (currentPos < this.fileSize) {
            // writeBuffer不为空则取 writeBuffer 剩下的空间，否则取 mappedByteBuffer 剩下的空间
            // writeBuffer 的 赋值在 init 方法，构造时不使用 TransientStorePool ，writeBuffeer 为 null
            ByteBuffer byteBuffer = writeBuffer != null ? writeBuffer.slice() : this.mappedByteBuffer.slice();
            byteBuffer.position(currentPos);
            AppendMessageResult result = null;
            if (messageExt instanceof MessageExtBrokerInner) {
                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);
    }

CommitLog$DefaultAppendMessageCallback非静态内部类中的方法

        /**
         * 1. 生成 messageId
         * 2. 获取offset
         * 3. 构造消息
         * 4. buffer put 方法 ，后续会刷入文件
         * @param fileFromOffset
         * @param byteBuffer
         * @param maxBlank
         * @param msgInner
         * @return
         */
        public AppendMessageResult doAppend(final long fileFromOffset, final ByteBuffer byteBuffer, final int maxBlank,
                                            final MessageExtBrokerInner msgInner) {
            // STORETIMESTAMP + STOREHOSTADDRESS + OFFSET <br>

            // 创建全局唯一消息ID
            // PHY OFFSET
            long wroteOffset = fileFromOffset + byteBuffer.position();

            this.resetByteBuffer(hostHolder, 8);
            String msgId = MessageDecoder.createMessageId(this.msgIdMemory, msgInner.getStoreHostBytes(hostHolder), wroteOffset);

            // Record ConsumeQueue information
            keyBuilder.setLength(0);
            keyBuilder.append(msgInner.getTopic());
            keyBuilder.append('-');
            keyBuilder.append(msgInner.getQueueId());
            String key = keyBuilder.toString();

            //获取该消息在消息队列的偏移量 。 CommitLog 中保存了当前所有消息队列的当
            //前待写入偏移量 。
            Long queueOffset = CommitLog.this.topicQueueTable.get(key);
            if (null == queueOffset) {
                queueOffset = 0L;
                CommitLog.this.topicQueueTable.put(key, queueOffset);
            }

            // Transaction messages that require special handling
            // 需要特殊处理的事务消息
            // 可以看到消息类型为 TRANSACTION_PREPARED_TYPE 或是 TRANSACTION_ROLLBACK_TYPE ,那么
            // 偏移量改为 0L
            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(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);
            }

            // 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(hostHolder, 8);
            this.msgStoreItemMemory.put(msgInner.getBornHostBytes(hostHolder));
            // 11 STORETIMESTAMP
            this.msgStoreItemMemory.putLong(msgInner.getStoreTimestamp());
            // 12 STOREHOSTADDRESS
            this.resetByteBuffer(hostHolder, 8);
            this.msgStoreItemMemory.put(msgInner.getStoreHostBytes(hostHolder));
            //this.msgBatchMemory.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((short) propertiesLength);
            if (propertiesLength > 0)
                this.msgStoreItemMemory.put(propertiesData);

            final long beginTimeMills = CommitLog.this.defaultMessageStore.now();
            // Write messages to the queue buffer
            // msgStoreItemMemory ：HeapByteBuffer  byteBuffer DirectByteBuffer。将消息从堆内内存转移到堆外内存。
            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;
        }

补充

堆内内存(HeapByteBuffer)就是我们常说的垃圾回收那部分的内存，而堆外内存(DirectByteBuffer)则是计算机分配给某个进程的内存，位于堆外,那么使用堆外内存的优势是什么呢？

1. 减少了垃圾回收
   
   堆外内存由于不在堆内，所以减少了垃圾会的工作，垃圾回收的时候会涨停其他工作。
2. 减去了复制的操作。
   
   堆内在flush到远程时，会先复制到直接内存（非堆内存），然后在发送；而堆外内存相当于省略掉了这个工作。(这一点就是零拷贝的知识点)

注意事项 ：

java.nio.DirectByteBuffer对象在创建过程中会先通过Unsafe接口直接通过os::malloc来分配内存，然后将内存的起始地址和大小存到java.nio.DirectByteBuffer对象里，这样就可以直接操作这些内存（即是说DirectByteBuffer 放着堆内对象的地址，当操作的时候实际是操作堆内对象）。这些内存只有在DirectByteBuffer回收掉之后才有机会被回收，因此如果这些对象大部分都移到了old，但是一直没有触发CMS GC或者Full GC，那么悲剧将会发生，因为你的物理内存被他们耗尽了，因此为了避免这种悲剧的发生，通过

-XX:MaxDirectMemorySize

来指定最大的堆外内存大小，当使用达到了阈值的时候将调用System.gc来做一次full gc，以此来回收掉没有被使用的堆外内存。摘自参考资料

总结

我们可以看到 RocketMQ 最主要就是利用映射文件的方法来提高读写效率。

参考资料

• https://blog.csdn.net/qq496013218/article/details/69397380
• 《Rocket源码分析》
• http://silence.work/2019/05/03/RocketMQ-Broker端处理消息过程分析/#more
• https://blog.csdn.net/ZYC88888/article/details/80228531