RocketMQ事务消息怎样实现
这篇文章主要介绍RocketMQ事务消息怎样实现,文中介绍的非常详细,具有一定的参考价值,感兴趣的小伙伴们一定要看完!
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RocketMQ4.3.0版本开始支持事务消息,后续分享将开始将剖析事务消息的实现原理。首先从官方给出的Demo实例入手,以此通往RocketMQ事务消息的世界中。
官方版本未发布之前,从apache rocketmq第一个版本上线后,代码中存在与事务消息相关的代码,例如COMMIT、ROLLBACK、PREPARED,在事务消息未开源之前网上对于事务消息的“声音”基本上是使用类似二阶段提交,主要是根据消息系统标志MessageSysFlag中定义来推测的:
TRANSACTION_PREPARED_TYPE
TRANSACTION_COMMIT_TYPE
TRANSACTION_ROLLBACK_TYPE
消息发送者首先发送TRANSACTION_PREPARED_TYPE类型的消息,然后根据事务状态来决定是提交或回滚事务发送commit请求或rollback请求,如果commit/rollback请求丢失后,rocketmq会在指定超时时间后回查事务状态来决定提交或回滚事务。
让我们各自带着自己的理解和猜测,从阅读RocketMQ官方提供的Demo程序入手,试图窥探一些大体的信息。
Demo示例程序位于:/rocketmq-example/src/main/java/org/apache/rocketmq/example/transaction包中。该包中未放置消息消费者,为了验证事务的消息消费情况,我们可以从其他包copy一个消费者,从而先运行生产者,然后运行消费者,判断事务消息的预发放、提交、回滚等效果,二话不说,先运行一下,看下效果再说:
消息发送端运行结果:
SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D5767EC0000, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=1], queueOffset=0] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D57680F0001, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=2], queueOffset=1] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D57681E0002, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=3], queueOffset=2] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D57682B0003, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=0], queueOffset=3] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D5768380004, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=1], queueOffset=4] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D5768490005, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=2], queueOffset=5] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D5768560006, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=3], queueOffset=6] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D5768640007, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=0], queueOffset=7] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D5768730008, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=1], queueOffset=8] SendResult [sendStatus=SEND_OK, msgId=C0A8010518DC6D06D69C8D5768800009, offsetMsgId=null, messageQueue=MessageQueue [topic=transaction_topic_test, brokerName=broker-a, queueId=2], queueOffset=9]
消息消费端效果:
Consumer Started. ConsumeMessageThread_1 Receive New Messages: [MessageExt [queueId=0, storeSize=325, queueOffset=0, sysFlag=8, bornTimestamp=1532745715812, bornHost=/192.168.1.5:55482, storeTimestamp=1532745749010, storeHost=/192.168.1.5:10911, msgId=C0A8010500002A9F0000000000001DE8, commitLogOffset=7656, bodyCRC=988340972, reconsumeTimes=0, preparedTransactionOffset=5477, toString()=Message{topic='transaction_topic_test', flag=0, properties={MIN_OFFSET=0, REAL_TOPIC=transaction_topic_test, TRANSACTION_CHECK_TIMES=1, MAX_OFFSET=1, KEYS=KEY7, TRAN_MSG=true, CONSUME_START_TIME=1532746024360, UNIQ_KEY=C0A8010518DC6D06D69C8D5768640007, WAIT=true, PGROUP=please_rename_unique_group_name, TAGS=TagC, REAL_QID=0}, body=[72, 101, 108, 108, 111, 32, 82, 111, 99, 107, 101, 116, 77, 81, 32, 55], transactionId='C0A8010518DC6D06D69C8D5768640007'}]] ConsumeMessageThread_2 Receive New Messages: [MessageExt [queueId=1, storeSize=325, queueOffset=0, sysFlag=8, bornTimestamp=1532745715768, bornHost=/192.168.1.5:55482, storeTimestamp=1532745749008, storeHost=/192.168.1.5:10911, msgId=C0A8010500002A9F0000000000001B91, commitLogOffset=7057, bodyCRC=601994070, reconsumeTimes=0, preparedTransactionOffset=4496, toString()=Message{topic='transaction_topic_test', flag=0, properties={MIN_OFFSET=0, REAL_TOPIC=transaction_topic_test, TRANSACTION_CHECK_TIMES=1, MAX_OFFSET=1, KEYS=KEY4, TRAN_MSG=true, CONSUME_START_TIME=1532746024361, UNIQ_KEY=C0A8010518DC6D06D69C8D5768380004, WAIT=true, PGROUP=please_rename_unique_group_name, TAGS=TagE, REAL_QID=1}, body=[72, 101, 108, 108, 111, 32, 82, 111, 99, 107, 101, 116, 77, 81, 32, 52], transactionId='C0A8010518DC6D06D69C8D5768380004'}]] ConsumeMessageThread_3 Receive New Messages: [MessageExt [queueId=2, storeSize=325, queueOffset=0, sysFlag=8, bornTimestamp=1532745715727, bornHost=/192.168.1.5:55482, storeTimestamp=1532745748834, storeHost=/192.168.1.5:10911, msgId=C0A8010500002A9F000000000000193A, commitLogOffset=6458, bodyCRC=1401636825, reconsumeTimes=0, preparedTransactionOffset=3515, toString()=Message{topic='transaction_topic_test', flag=0, properties={MIN_OFFSET=0, REAL_TOPIC=transaction_topic_test, TRANSACTION_CHECK_TIMES=1, MAX_OFFSET=1, KEYS=KEY1, TRAN_MSG=true, CONSUME_START_TIME=1532746024368, UNIQ_KEY=C0A8010518DC6D06D69C8D57680F0001, WAIT=true, PGROUP=please_rename_unique_group_name, TAGS=TagB, REAL_QID=2}, body=[72, 101, 108, 108, 111, 32, 82, 111, 99, 107, 101, 116, 77, 81, 32, 49], transactionId='C0A8010518DC6D06D69C8D57680F0001'}]]
综上所述,服务端发送了10条消息,而消费端只收到3条消息,应该是由于事务回滚,造成只提交了3条消息,为了更加严谨,可以安装一个rocketmq-consonse,更加直观的观察shangshagn's上述结果:
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接下来对示例代码进行解读:
1、生产者端代码解读:
public class TransactionProducer { public static void main(String[] args) throws MQClientException, InterruptedException { TransactionListener transactionListener = new TransactionListenerImpl(); // @1 TransactionMQProducer producer = new TransactionMQProducer("please_rename_unique_group_name"); producer.setNamesrvAddr("127.0.0.1:9876"); ExecutorService executorService = new ThreadPoolExecutor(2, 5, 100, TimeUnit.SECONDS, new ArrayBlockingQueue(2000), new ThreadFactory() { @Override public Thread newThread(Runnable r) { Thread thread = new Thread(r); thread.setName("client-transaction-msg-check-thread"); return thread; } }); // @2 producer.setExecutorService(executorService); // @3 producer.setTransactionListener(transactionListener); // @4 producer.start(); String[] tags = new String[] {"TagA", "TagB", "TagC", "TagD", "TagE"}; for (int i = 0; i < 10; i++) { // @5 try { Message msg = new Message("transaction_topic_test", tags[i % tags.length], "KEY" + i, ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET)); SendResult sendResult = producer.sendMessageInTransaction(msg, null); System.out.printf("%s%n", sendResult); Thread.sleep(10); } catch (MQClientException | UnsupportedEncodingException e) { e.printStackTrace(); } } for (int i = 0; i < 100000; i++) { //这里只是阻止生产者过早退出,导致事务消息的相关机制无法运行 Thread.sleep(1000); } producer.shutdown(); } }
代码@1:创建TransactionListener 实例,字面理解为事务消息事件监听器,下文详细对其进行展开。
代码@2:ExecutorService
executorService,创建一个线程池,其线程的名称前缀”client-transaction-msg-check-thread“,从字面理解为客户端事务消息状态检测线程,我们可以大胆的猜测一下是不是这个线程池调用TransactionListener方法,完成对事务消息的检测呢?【这里只是作者的猜测,大家不能当真,在作者后续文章发布后,如果该观点错误,会加以修复,这里写出来,主要是想分享一下我读源码的方法】。
代码@3:为事务消息发送者设置线程池。
代码@4:为事务消息发送者设置事务监听器。
代码@5:发送10条消息。
2、TransactionListener代码解读
public class TransactionListenerImpl implements TransactionListener { private AtomicInteger transactionIndex = new AtomicInteger(0); private ConcurrentHashMaplocalTrans = new ConcurrentHashMap<>(); @Override public LocalTransactionState executeLocalTransaction(Message msg, Object arg) { int value = transactionIndex.getAndIncrement(); int status = value % 3; localTrans.put(msg.getTransactionId(), status); return LocalTransactionState.UNKNOW; } @Override public LocalTransactionState checkLocalTransaction(MessageExt msg) { Integer status = localTrans.get(msg.getTransactionId()); if (null != status) { switch (status) { case 0: return LocalTransactionState.UNKNOW; case 1: return LocalTransactionState.COMMIT_MESSAGE; case 2: return LocalTransactionState.ROLLBACK_MESSAGE; } } return LocalTransactionState.COMMIT_MESSAGE; } }
executeLocalTransaction方法:记录本地事务的事务状态,这里其实现就是循环设置事务消息的状态为0,1,2,demo中是把消息的状态数据存放在一个Map中。实际应用时通常会持久化消息的事务状态,例如数据库或缓存。
checkLocalTransaction方法,事务回查业务实现,查本地事务表,判断事务的状态如为0:UNKNOW,1:COMMIT_MESSAGE;ROLLBACK_MESSAGE。这里就能解释,生产者连续发10条消息,因为只有3条消息的事务状态为COMMIT_MESSAGE,故消息消费者只能消费3条。
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