【RocketMQ】msgId与offsetMsgId

一. 概念

1. msgId(uniqId)

producer客户端 生成,调用方法MessageClientIDSetter.createUniqID()生成全局唯一的Id


    private static final int LEN;
    private static final String FIX_STRING;
    private static final AtomicInteger COUNTER;
    private static long startTime;
    private static long nextStartTime;

    public static String createUniqID() {

        StringBuilder sb = new StringBuilder(LEN * 2);
        sb.append(FIX_STRING);   // 固定值,程序启动时生成
        sb.append(UtilAll.bytes2string(createUniqIDBuffer())); // 变化值 根据时间差+自增长生成
        return sb.toString();
    }
  1. FIX_STRING 固定前缀
  2. 生成规则:客户端的IP、进程ID、MessageClientIDSetter类加载器的hashcode
    static {
        byte[] ip;
        try {
            ip = UtilAll.getIP();
        } catch (Exception e) {
            ip = createFakeIP();
        }
        LEN = ip.length + 2 + 4 + 4 + 2;
        ByteBuffer tempBuffer = ByteBuffer.allocate(ip.length + 2 + 4);
        tempBuffer.put(ip);                                 // 客户端IP
        tempBuffer.putShort((short) UtilAll.getPid());      // 进程ID
        tempBuffer.putInt(MessageClientIDSetter.class.getClassLoader().hashCode()); // 类加载器hashCode
        FIX_STRING = UtilAll.bytes2string(tempBuffer.array());
        setStartTime(System.currentTimeMillis());
        COUNTER = new AtomicInteger(0);
    }

     private synchronized static void setStartTime(long millis) {
        Calendar cal = Calendar.getInstance();
        cal.setTimeInMillis(millis);
        cal.set(Calendar.DAY_OF_MONTH, 1);
        cal.set(Calendar.HOUR_OF_DAY, 0);
        cal.set(Calendar.MINUTE, 0);
        cal.set(Calendar.SECOND, 0);
        cal.set(Calendar.MILLISECOND, 0);
        startTime = cal.getTimeInMillis();
        cal.add(Calendar.MONTH, 1);
        nextStartTime = cal.getTimeInMillis();
    }

    // 获取进程ID
    public static int getPid() {
        RuntimeMXBean runtime = ManagementFactory.getRuntimeMXBean();
        String name = runtime.getName(); // format: "pid@hostname"
        try {
            return Integer.parseInt(name.substring(0, name.indexOf('@')));
        } catch (Exception e) {
            return -1;
        }
    }
  1. createUniqIDBuffer 变化值
  2. 生成规则:当前时间与系统启动时间的差值,以及自增序号

   private static byte[] createUniqIDBuffer() {
        ByteBuffer buffer = ByteBuffer.allocate(4 + 2);
        long current = System.currentTimeMillis();

        // 每月1号重新计算 startTime,避免时间戳差值无限增加
        if (current >= nextStartTime) {
            setStartTime(current);
        }

        // 时间差值(当前时间戳-系统启动时时间戳)
        buffer.putInt((int) (System.currentTimeMillis() - startTime));

         // 1. short:毫秒内自增长,几万够了 
         // 2. COUNTER达到最大值后,会从最大的负数开始递增,如-2147483648 -2147483647

        buffer.putShort((short) COUNTER.getAndIncrement());
        return buffer.array();
    }

2. offsetMsgId

  1. Broker 服务端将消息追加到内存后会返回其物理偏移量,即在 commitlog 文件中的偏移量,然后会生成一个id,代码中虽然也叫 msgId,其实是 offsetMsgId
  2. 组成规则:Broker 服务器的 IP 与端口号、消息的物理偏移量
  • ByteBuffer input: 用来存放 offsetMsgId 的字节缓存区
  • ByteBuffer addr: Broker 服务器的 IP 地址与端口号,即通过解析 offsetMsgId 从而得到消息服务器的地址信息
  • long offset:消息的物理偏移量
    类:org.apache.rocketmq.common.message.MessageDecoder

    public static String createMessageId(final ByteBuffer input, final ByteBuffer addr, final long offset) {
        input.flip();
        int msgIDLength = addr.limit() == 8 ? 16 : 28;
        input.limit(msgIDLength);

        input.put(addr);
        input.putLong(offset);

        return UtilAll.bytes2string(input.array());
    }

二. 消息发送

其中包含了msgId、offsetMsgId
image

三. 消息消费

image

  1. 消费客户端返回的对象是 MessageClientExt ,继承自 MessageExt ,MessageExt继承自 Message
  2. 如果消息消费失败需要重试,RocketMQ 的做法是将消息重新发送到 Broker 服务器,此时 msgId 是不会发生变化的,但该消息的 offsetMsgId 会发生变化,因为其存储在 Broker 服务器中的位置发生了变化
  3. 在调用 MessageClientExt 中的 getMsgId() 方法时,先返回消息属性中的MsgId,不存在则返回消息的 offsetMsgId
public String getMsgId() {
    String uniqID = MessageClientIDSetter.getUniqID(this);
    if (uniqID == null) {
        return this.getOffsetMsgId();
    } else {
        return uniqID;
    }
}
  1. MessageExt 的toString 方法
    public String toString() {
        return "MessageExt [brokerName=" + brokerName + ", queueId=" + queueId + ", storeSize=" + storeSize + ", queueOffset=" + queueOffset
            + ", sysFlag=" + sysFlag + ", bornTimestamp=" + bornTimestamp + ", bornHost=" + bornHost
            + ", storeTimestamp=" + storeTimestamp + ", storeHost=" + storeHost + ", msgId=" + msgId
            + ", commitLogOffset=" + commitLogOffset + ", bodyCRC=" + bodyCRC + ", reconsumeTimes="
            + reconsumeTimes + ", preparedTransactionOffset=" + preparedTransactionOffset
            + ", toString()=" + super.toString() + "]";
    }
  1. MessageClientExt类( 本类没有重写toString()方法,调用的是父类MessageExt的方法)
public class MessageClientExt extends MessageExt {

    public String getOffsetMsgId() {
        return super.getMsgId();
    }

    public void setOffsetMsgId(String offsetMsgId) {
        super.setMsgId(offsetMsgId);
    }

    @Override
    public String getMsgId() {
        String uniqID = MessageClientIDSetter.getUniqID(this);
        if (uniqID == null) {
            return this.getOffsetMsgId();
        } else {
            return uniqID;
        }
    }

    public void setMsgId(String msgId) {
        //DO NOTHING
        //MessageClientIDSetter.setUniqID(this);
    }
}

四. Dashboard根据ID查询

  1. 界面显示的是 msgId,即uniqId
  2. RocketMQ会先调用queryMsgById方法,先通过msgId查询,查询无结果再通过 offsetMsgId 查询
  3. 界面新增显示 offsetMsgId 字段
    MessageServiceImpl.viewMessage
    
    String offsetMsgId = ((MessageClientExt) messageExt).getOffsetMsgId();
    messageView.setOffsetMsgId(offsetMsgId);
posted @ 2021-09-14 18:18    阅读(186)  评论(0编辑  收藏  举报