msgId:C0A83B6000002A9F00000000000003D9

    来源：responseHeader.getMsgId(), responseHeader.getQueueOffset()

    由RemotingCommand的extFields字段提供，其他字段如下：
    private int code; 见 ResponseCode 类说明
    private LanguageCode language = LanguageCode.JAVA;
    private int version = 0;
    private int opaque = requestId.getAndIncrement();
    private int flag = 0;
    private String remark;
    private HashMap extFields;
    private transient CommandCustomHeader customHeader;

    发送消息的code=310

    NettyRemotingAbstract的方法processMessageReceived方法会接受这个处理。

    netty接收到了请求，拿到了pair
    left class:org.apache.rocketmq.broker.processor.SendMessageProcessor
    right class:org.apache.rocketmq.broker.latency.BrokerFixedThreadPoolExecutor

    SendMessageProcessor —> DefaultMessageStore —> CommitLog

    MappedFile fileName:/Users/shuishan/store/commitlog/00000000000000000000
    result = mappedFile.appendMessage(msg, this.appendMessageCallback);

    fileSize:1073741824
    currentPos:2561
    msgId:MessageDecoder.createMessageId C0A83B6000002A9F0000000000000A01