RocketMQ存储篇一：概览

这篇文章记录RocketMQ大致的存储流程，源码为5.0.1-SNAPSHOT

入口从Broker模块的SendMessageProcessor开始
@SendMessageProcessor#sendMessage()

5.0中将putmessage中的一些校验逻辑下沉到了hook中

for (PutMessageHook putMessageHook : putMessageHookList) {
            PutMessageResult handleResult = putMessageHook.executeBeforePutMessage(msg);
            if (handleResult != null) {
                return CompletableFuture.completedFuture(handleResult);
            }
        }

1. store服务关闭会fail
2. slave as master模式中slave不可用会fail
3. store不可写会fail
4. 非重试topic超过最大长度会失败（Byte 127）
5. topic长度超过255会失败
6. msg body为空会fail
7. pagecache busy会fail

然后会调用commitlog中的putMessage方法

重点看一下这里面的逻辑
@commitLog#asyncPutMessage(msg)

1. 编码消息
   PutMessageResult encodeResult = putMessageThreadLocal.getEncoder().encode(msg);

    public PutMessageResult encode(MessageExtBrokerInner msgInner) {
        this.byteBuf.clear();
		//忽略不重要逻辑
        // 1 TOTALSIZE
        this.byteBuf.writeInt(msgLen);
        // 2 MAGICCODE
        this.byteBuf.writeInt(msgInner.getVersion().getMagicCode());
        // 3 BODYCRC
        this.byteBuf.writeInt(msgInner.getBodyCRC());
        // 4 QUEUEID
        this.byteBuf.writeInt(msgInner.getQueueId());
        // 5 FLAG
        this.byteBuf.writeInt(msgInner.getFlag());
        // 6 QUEUEOFFSET 这里先填占位，后面doappend的时候再写入真实的queueOffset
        this.byteBuf.writeLong(queueOffset);
        // 7 PHYSICALOFFSET, need update later；这里也是先占位，然后doappend的时候更新消息的真实offset
        this.byteBuf.writeLong(0);
        // 8 SYSFLAG
        this.byteBuf.writeInt(msgInner.getSysFlag());
        // 9 BORNTIMESTAMP
        this.byteBuf.writeLong(msgInner.getBornTimestamp());

        // 10 BORNHOST
        ByteBuffer bornHostBytes = msgInner.getBornHostBytes();
        this.byteBuf.writeBytes(bornHostBytes.array());

        // 11 STORETIMESTAMP
        this.byteBuf.writeLong(msgInner.getStoreTimestamp()); //后续更新

        // 12 STOREHOSTADDRESS
        ByteBuffer storeHostBytes = msgInner.getStoreHostBytes();  //..
        this.byteBuf.writeBytes(storeHostBytes.array());

        // 13 RECONSUMETIMES
        this.byteBuf.writeInt(msgInner.getReconsumeTimes());
        // 14 Prepared Transaction Offset
        this.byteBuf.writeLong(msgInner.getPreparedTransactionOffset());
        // 15 BODY
        this.byteBuf.writeInt(bodyLength);
        if (bodyLength > 0)
            this.byteBuf.writeBytes(msgInner.getBody());

        // 16 TOPIC
        if (MessageVersion.MESSAGE_VERSION_V2.equals(msgInner.getVersion())) {
            this.byteBuf.writeShort((short) topicLength);
        } else {
            this.byteBuf.writeByte((byte) topicLength);
        }
        this.byteBuf.writeBytes(topicData);

        // 17 PROPERTIES
        this.byteBuf.writeShort((short) propertiesLength);
        if (propertiesLength > 0)
            this.byteBuf.writeBytes(propertiesData);

        return null;
    }

这里表明了RocketMQ中消息的定义，组成结构为

2. 对topic-queue加锁
   对putMessageLock加锁

3. 获取mappedFile
   mappedFile = this.mappedFileQueue.getLastMappedFile(0); // Mark: NewFile may be cause noise
   关于commitlog、mappedFile等介绍，参见文章《》

4. 写入mappedFile
   result = mappedFile.appendMessage(msg, this.appendMessageCallback, putMessageContext);
   核心方法，传入一个msg，回调函数以及上下文，将消息写入pagecache，然后调用callback中的doAppend方法写入

5. 数据统计
   // Statistics
   storeStatsService.getSinglePutMessageTopicTimesTotal(msg.getTopic()).add(result.getMsgNum());
   storeStatsService.getSinglePutMessageTopicSizeTotal(topic).add(result.getWroteBytes());

6. 处理刷盘以及主从同步
   handleDiskFlushAndHA(putMessageResult, msg, needAckNums, needHandleHA);