RocketMQ事务消息原理简析
零、业务场景
在项目中，经常遇到这样一个场景，需要保证数据持久化和消息发送要么同时成功，要么同时失败。比如当用户在交易系统下了一个订单，购物车需要消费订单消息清除加购数据、积分系统需要变更用户积分、短信平台需要给买家发送提醒等，交易系统要将订单落入DB和发送订单消息保证一致，不能本地事务回滚，订单没有生成但是发送了创建订单消息，下游系统产生脏数据，也不能订单已经创建，但是下游系统没有感知继而无法履约，影响用户体验。
如果让我们自己实现的话，当然也是有办法的。比如在业务数据库中建立一张消息表用于存储消息，将业务数据和消息数据放在同一个事务中进行存储，就可以利用数据库事务保证同时原子性。后续可以定时扫描消息表，将消息数据再发送出去。
当然也可以用现成的解决方案，RocketMQ从4.3.0版本开始，支持事务消息。我们只需要编写对应的本地事务执行方法executeLocalTransaction和本地事务执行结果检查方法checkLocalTransaction，RocketMQ会自动调用本地事务执行。如果本地事务执行成功，下游才能消费到消息，如果本地事务执行失败，下游是无法感知到这条消息的
一、使用方法
使用RocketMQ发送事务消息，只有消息发送和普通消息发送有所区别。参见官方示例：
// TransactionProducer.java
// 需要自定义一个TransactionListener用于执行事务executeLocalTransaction和事务执行结果回查checkLocalTransaction 代码在下面
TransactionListener transactionListener = new TransactionListenerImpl();
// 事务消息发送producer
TransactionMQProducer producer = new TransactionMQProducer(PRODUCER_GROUP);
producer.setNamesrvAddr(DEFAULT_NAMESRVADDR);
// 创建一个线程池 用于Broker回查本地事务执行状态 如果这里没有创建，RocketMQ会自动创建一个线程池
ExecutorService executorService = new ThreadPoolExecutor(2, 5, 100, TimeUnit.SECONDS, new ArrayBlockingQueue<>(2000), r -> {
Thread thread = new Thread(r);
thread.setName("client-transaction-msg-check-thread");
return thread;
});
producer.setExecutorService(executorService);
producer.setTransactionListener(transactionListener);
producer.start();
String[] tags = new String[] {"TagA", "TagB", "TagC", "TagD", "TagE"};
for (int i = 0; i < MESSAGE_COUNT; i++) {
try {
Message msg =
new Message(TOPIC, tags[i % tags.length], "KEY" + i,
("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET));
// 发送事务消息
SendResult sendResult = producer.sendMessageInTransaction(msg, null);
System.out.printf("%s%n", sendResult);
Thread.sleep(10);
} catch (MQClientException | UnsupportedEncodingException e) {
e.printStackTrace();
}
}
public class TransactionListenerImpl implements TransactionListener {
private AtomicInteger transactionIndex = new AtomicInteger(0);
private ConcurrentHashMap<String, Integer> localTrans = new ConcurrentHashMap<>();
/**
* 执行本地事务
*/
@Override
public LocalTransactionState executeLocalTransaction(Message msg, Object arg) {
int value = transactionIndex.getAndIncrement();
int status = value % 3;
localTrans.put(msg.getTransactionId(), status);
return LocalTransactionState.UNKNOW;
}
/**
* 本地事务执行状态回查
*/
@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;
default:
return LocalTransactionState.COMMIT_MESSAGE;
}
}
return LocalTransactionState.COMMIT_MESSAGE;
}
}
本地事务的执行状态，有三种结果：
- LocalTransactionState.COMMIT_MESSAGE：事务执行成功，Broker会处理消息供下游消费
- LocalTransactionState.ROLLBACK_MESSAGE：事务被回滚，Broker会删除消息，下游感知不到消息
- LocalTransactionState.UNKNOW：事务的执行结果未知，比如事务还在执行中，稍后Broker会回重复回查，直到超过最大时间或者最大次数
二、原理解析
0、整体流程
- Producer发送事务消息
- Broker端SendMessageProcessor收到消息后，判断如果是一条事务消息，会将消息原来的topic和队列id存储到消息拓展中，设置新的topic为RMQ_SYS_TRANS_HALF_TOPIC然后 进行存储，然后通知Producer
- Producer收到Broker消息发送成功后，开始执行本地事务
- 本地事务执行完毕，Producer将事务执行状态通知Broker
- Broker端EndTransactionProcessor收到事务执行状态，从RMQ_SYS_TRANS_HALF_TOPIC中取出消息。如果事务执行成功，则从消息拓展中取出原本的topic和队列id，存储到真实的topic和队列id中，存储到RMQ_SYS_TRANS_OP_HALF_TOPIC主题中；如果是事务回滚，只把消息存储到RMQ_SYS_TRANS_OP_HALF_TOPIC主题中
- 如果Broker没有收到Producer事务执行状态的通知，Broker端TransactionalMessageCheckService会主动定时从RMQ_SYS_TRANS_HALF_TOPIC中捞取消息，判断是否有需要回查的消息
- 如果有需要回查的消息，Broker端TransactionalMessageCheckService会向Producer回查事务状态
- Producer执行TransactionListener的checkLocalTransaction方法，查询事务执行状态
- Producer查询本地事务状态之后再执行上述第4步和第5步
1、Producer发送消息
// 编写TransactionListener实现类用于执行本地事务和本地事务回查
TransactionListener transactionListener = new TransactionListenerImpl();
// 发送事务消息专用的TransactionMQProducer
TransactionMQProducer producer = new TransactionMQProducer(PRODUCER_GROUP);
producer.setNamesrvAddr(DEFAULT_NAMESRVADDR);
// 新建一个线程池用于异步执行从Broker过来的事务回查 如果这里不新建 Broker也会自动创建一个
ExecutorService executorService = new ThreadPoolExecutor(2, 5, 100, TimeUnit.SECONDS, new ArrayBlockingQueue<>(2000), r -> {
Thread thread = new Thread(r);
thread.setName("client-transaction-msg-check-thread");
return thread;
});
producer.setExecutorService(executorService);
producer.setTransactionListener(transactionListener);
producer.start();
String[] tags = new String[] {"TagA", "TagB", "TagC", "TagD", "TagE"};
for (int i = 0; i < MESSAGE_COUNT; i++) {
try {
Message msg =
new Message(TOPIC, tags[i % tags.length], "KEY" + i,
("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET));
// 发送事务消息
SendResult sendResult = producer.sendMessageInTransaction(msg, null);
System.out.printf("%s%n", sendResult);
Thread.sleep(10);
} catch (MQClientException | UnsupportedEncodingException e) {
e.printStackTrace();
}
}
// 发送事务消息
public TransactionSendResult sendMessageInTransaction(final Message msg,
final LocalTransactionExecuter localTransactionExecuter, final Object arg)
throws MQClientException {
// 校验是否设置TransactionListener 发送事务消息必须要有TransactionListener
TransactionListener transactionListener = getCheckListener();
if (null == localTransactionExecuter && null == transactionListener) {
throw new MQClientException("tranExecutor is null", null);
}
// ignore DelayTimeLevel parameter
if (msg.getDelayTimeLevel() != 0) {
// 事务消息不支持延迟发送
MessageAccessor.clearProperty(msg, MessageConst.PROPERTY_DELAY_TIME_LEVEL);
}
Validators.checkMessage(msg, this.defaultMQProducer);
SendResult sendResult = null;
// 标记prepare消息 Broker根据这个判断是否是一条事务消息
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_TRANSACTION_PREPARED, "true");
// 设置消息生产者组 为了查询事务消息本地事务状态时 从该生产者组中随机选择一个消息生产者即可
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_PRODUCER_GROUP, this.defaultMQProducer.getProducerGroup());
try {
sendResult = this.send(msg);
} catch (Exception e) {
throw new MQClientException("send message Exception", e);
}
// ......
// 对发送结果的处理稍后解析
}
2、Broker接收事务消息
// asyncSendMessage方法
CompletableFuture<PutMessageResult> putMessageResult = null;
// 依据消息是否有MessageConst.PROPERTY_TRANSACTION_PREPARED判断是否事务消息
String transFlag = origProps.get(MessageConst.PROPERTY_TRANSACTION_PREPARED);
if (Boolean.parseBoolean(transFlag)) {
// 处理事务消息
if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) {
response.setCode(ResponseCode.NO_PERMISSION);
response.setRemark(
"the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1()
+ "] sending transaction message is forbidden");
return CompletableFuture.completedFuture(response);
}
// 保存事务消息
putMessageResult = this.brokerController.getTransactionalMessageService().asyncPrepareMessage(msgInner);
} else {
// 保存消息
putMessageResult = this.brokerController.getMessageStore().asyncPutMessage(msgInner);
}
private MessageExtBrokerInner parseHalfMessageInner(MessageExtBrokerInner msgInner) {
// 备份原本的topic和队列
MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_TOPIC, msgInner.getTopic());
MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_QUEUE_ID,
String.valueOf(msgInner.getQueueId()));
msgInner.setSysFlag(
MessageSysFlag.resetTransactionValue(msgInner.getSysFlag(), MessageSysFlag.TRANSACTION_NOT_TYPE));
// 设置新的topic为RMQ_SYS_TRANS_HALF_TOPIC
msgInner.setTopic(TransactionalMessageUtil.buildHalfTopic());
// 队列是写死的 只有一个 也就是说是顺序处理的
msgInner.setQueueId(0);
msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgInner.getProperties()));
return msgInner;
}
3、Producer处理发送消息结果
// sendMessageInTransaction方法
try {
// 事务消息发送结果
sendResult = this.send(msg);
} catch (Exception e) {
throw new MQClientException("send message Exception", e);
}
LocalTransactionState localTransactionState = LocalTransactionState.UNKNOW;
Throwable localException = null;
// 处理事务消息发送结果
switch (sendResult.getSendStatus()) {
// 发送成功的情况
case SEND_OK: {
try {
if (sendResult.getTransactionId() != null) {
msg.putUserProperty("__transactionId__", sendResult.getTransactionId());
}
String transactionId = msg.getProperty(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX);
if (null != transactionId && !"".equals(transactionId)) {
msg.setTransactionId(transactionId);
}
if (null != localTransactionExecuter) {
// 这个已经废弃了 不会进入这里
localTransactionState = localTransactionExecuter.executeLocalTransactionBranch(msg, arg);
} else if (transactionListener != null) {
// 这里执行本地事务
log.debug("Used new transaction API");
localTransactionState = transactionListener.executeLocalTransaction(msg, arg);
}
if (null == localTransactionState) {
localTransactionState = LocalTransactionState.UNKNOW;
}
if (localTransactionState != LocalTransactionState.COMMIT_MESSAGE) {
log.info("executeLocalTransactionBranch return {}", localTransactionState);
log.info(msg.toString());
}
} catch (Throwable e) {
// 有catch逻辑 是考虑到事务执行异常的场景
log.info("executeLocalTransactionBranch exception", e);
log.info(msg.toString());
localException = e;
}
}
break;
case FLUSH_DISK_TIMEOUT:
case FLUSH_SLAVE_TIMEOUT:
case SLAVE_NOT_AVAILABLE:
localTransactionState = LocalTransactionState.ROLLBACK_MESSAGE;
break;
default:
break;
}
4、Producer通知Broker事务执行状态
try {
// 事务消息收尾工作 通知Broker干活
this.endTransaction(msg, sendResult, localTransactionState, localException);
} catch (Exception e) {
log.warn("local transaction execute " + localTransactionState + ", but end broker transaction failed", e);
}
public void endTransaction(
final Message msg,
final SendResult sendResult,
final LocalTransactionState localTransactionState,
final Throwable localException) throws RemotingException, MQBrokerException, InterruptedException, UnknownHostException {
final MessageId id;
if (sendResult.getOffsetMsgId() != null) {
id = MessageDecoder.decodeMessageId(sendResult.getOffsetMsgId());
} else {
id = MessageDecoder.decodeMessageId(sendResult.getMsgId());
}
String transactionId = sendResult.getTransactionId();
final String brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(sendResult.getMessageQueue().getBrokerName());
EndTransactionRequestHeader requestHeader = new EndTransactionRequestHeader();
requestHeader.setTransactionId(transactionId);
requestHeader.setCommitLogOffset(id.getOffset());
// 设置本地事务执行状态
switch (localTransactionState) {
case COMMIT_MESSAGE:
requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_COMMIT_TYPE);
break;
case ROLLBACK_MESSAGE:
requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_ROLLBACK_TYPE);
break;
case UNKNOW:
requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_NOT_TYPE);
break;
default:
break;
}
doExecuteEndTransactionHook(msg, sendResult.getMsgId(), brokerAddr, localTransactionState, false);
requestHeader.setProducerGroup(this.defaultMQProducer.getProducerGroup());
requestHeader.setTranStateTableOffset(sendResult.getQueueOffset());
requestHeader.setMsgId(sendResult.getMsgId());
String remark = localException != null ? ("executeLocalTransactionBranch exception: " + localException.toString()) : null;
// 发送消息给Broker
this.mQClientFactory.getMQClientAPIImpl().endTransactionOneway(brokerAddr, requestHeader, remark,
this.defaultMQProducer.getSendMsgTimeout());
}
public void endTransactionOneway(
final String addr,
final EndTransactionRequestHeader requestHeader,
final String remark,
final long timeoutMillis
) throws RemotingException, InterruptedException {
// 指定Broker使用EndTransactionProcessor处理
RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.END_TRANSACTION, requestHeader);
request.setRemark(remark);
// 单向消息 不考虑发送结果
// 也就是说 是可能发送失败的 发送失败之后Broker会回查
this.remotingClient.invokeOneway(addr, request, timeoutMillis);
}
5、Broker处理事务执行状态通知
// processRequest方法
// 上面的代理是Broker向Producer回查事务后的处理 稍后解析
else {
// 发送半消息之后产生的调用
switch (requestHeader.getCommitOrRollback()) {
// 如果事务执行不是commit或者rollback 直接返回 不再进行下面的逻辑
case MessageSysFlag.TRANSACTION_NOT_TYPE: {
LOGGER.warn("The producer[{}] end transaction in sending message, and it's pending status."
+ "RequestHeader: {} Remark: {}",
RemotingHelper.parseChannelRemoteAddr(ctx.channel()),
requestHeader.toString(),
request.getRemark());
return null;
}
// 如果事务执行是commit 接着下面的处理
case MessageSysFlag.TRANSACTION_COMMIT_TYPE: {
break;
}
// 如果事务执行是rollback 打印异常日志 接着下面的处理
case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE: {
LOGGER.warn("The producer[{}] end transaction in sending message, rollback the message."
+ "RequestHeader: {} Remark: {}",
RemotingHelper.parseChannelRemoteAddr(ctx.channel()),
requestHeader.toString(),
request.getRemark());
break;
}
default:
return null;
}
}
OperationResult result = new OperationResult();
if (MessageSysFlag.TRANSACTION_COMMIT_TYPE == requestHeader.getCommitOrRollback()) {
// 根据偏移量 取出topic是RMQ_SYS_TRANS_HALF_TOPIC的消息
// 第2步Broker保存消息之后 会把偏移量通知Producer Producer再传到这里
result = this.brokerController.getTransactionalMessageService().commitMessage(requestHeader);
// 事务执行状态是commit
if (result.getResponseCode() == ResponseCode.SUCCESS) {
RemotingCommand res = checkPrepareMessage(result.getPrepareMessage(), requestHeader);
if (res.getCode() == ResponseCode.SUCCESS) {
// 从消息中取出原来的topic和队列等信息 构建真实消息
MessageExtBrokerInner msgInner = endMessageTransaction(result.getPrepareMessage());
msgInner.setSysFlag(MessageSysFlag.resetTransactionValue(msgInner.getSysFlag(), requestHeader.getCommitOrRollback()));
msgInner.setQueueOffset(requestHeader.getTranStateTableOffset());
msgInner.setPreparedTransactionOffset(requestHeader.getCommitLogOffset());
msgInner.setStoreTimestamp(result.getPrepareMessage().getStoreTimestamp());
// 清除事务消息相关标记 防止循环处理
MessageAccessor.clearProperty(msgInner, MessageConst.PROPERTY_TRANSACTION_PREPARED);
// 保存真实消息
RemotingCommand sendResult = sendFinalMessage(msgInner);
if (sendResult.getCode() == ResponseCode.SUCCESS) {
// 删除消息RMQ_SYS_TRANS_HALF_TOPIC
// 实际上是投递到RMQ_SYS_TRANS_OP_HALF_TOPIC中 并标记删除
// 这里为什么还要投递到RMQ_SYS_TRANS_OP_HALF_TOPIC中 不直接删除呢 后面还需要根据这个判断是否是重复处理等
this.brokerController.getTransactionalMessageService().deletePrepareMessage(result.getPrepareMessage());
}
return sendResult;
}
return res;
}
} else if (MessageSysFlag.TRANSACTION_ROLLBACK_TYPE == requestHeader.getCommitOrRollback()) {
// 如果事务状态是rollback 删除消息RMQ_SYS_TRANS_HALF_TOPIC 投递到RMQ_SYS_TRANS_OP_HALF_TOPIC中并标记删除
// 比commit少了一个投递真实主题的步骤
result = this.brokerController.getTransactionalMessageService().rollbackMessage(requestHeader);
if (result.getResponseCode() == ResponseCode.SUCCESS) {
RemotingCommand res = checkPrepareMessage(result.getPrepareMessage(), requestHeader);
if (res.getCode() == ResponseCode.SUCCESS) {
this.brokerController.getTransactionalMessageService().deletePrepareMessage(result.getPrepareMessage());
}
return res;
}
}
6、Broker主动捞取消息
TransactionalMessageCheckService类实现Runnable接口，在Broker启动的时候，回调用BrokerController的start方法，在start方法中，会调用TransactionalMessageCheckService的start方法启动线程，run方法是一个死循环，默认每6秒执行一次
public void run() {
log.info("Start transaction check service thread!");
long checkInterval = brokerController.getBrokerConfig().getTransactionCheckInterval();
while (!this.isStopped()) {
this.waitForRunning(checkInterval);
}
log.info("End transaction check service thread!");
}
循环中实际执行的是这个方法
protected void onWaitEnd() {
// 事务过期时间 只有当消息存储时间加上这个过期时间大于系统当前时间 才对消息执行事务回查 否则在下一次周期中执行事务回查操作
long timeout = brokerController.getBrokerConfig().getTransactionTimeOut();
// 事务回查最大检测次数 如果超过最大检测次数还是无法获知消息的事务状态 不会再会回查 直接丢弃相当于回滚事务
int checkMax = brokerController.getBrokerConfig().getTransactionCheckMax();
long begin = System.currentTimeMillis();
log.info("Begin to check prepare message, begin time:{}", begin);
this.brokerController.getTransactionalMessageService().check(timeout, checkMax, this.brokerController.getTransactionalMessageCheckListener());
log.info("End to check prepare message, consumed time:{}", System.currentTimeMillis() - begin);
}
public void check(long transactionTimeout, int transactionCheckMax,
AbstractTransactionalMessageCheckListener listener) {
try {
// 获取事务半消息主题下的全部队列 然后依次处理
String topic = TopicValidator.RMQ_SYS_TRANS_HALF_TOPIC;
Set<MessageQueue> msgQueues = transactionalMessageBridge.fetchMessageQueues(topic);
if (msgQueues == null || msgQueues.size() == 0) {
log.warn("The queue of topic is empty :" + topic);
return;
}
log.debug("Check topic={}, queues={}", topic, msgQueues);
for (MessageQueue messageQueue : msgQueues) {
long startTime = System.currentTimeMillis();
MessageQueue opQueue = getOpQueue(messageQueue);
// RMQ_SYS_TRANS_HALF_TOPIC消息消费进度
long halfOffset = transactionalMessageBridge.fetchConsumeOffset(messageQueue);
// 收到事务消息提交或者回滚请求后的MQ_SYS_TRANS_OP_HALF_TOPIC中消息消费进度
long opOffset = transactionalMessageBridge.fetchConsumeOffset(opQueue);
log.info("Before check, the queue={} msgOffset={} opOffset={}", messageQueue, halfOffset, opOffset);
if (halfOffset < 0 || opOffset < 0) {
log.error("MessageQueue: {} illegal offset read: {}, op offset: {},skip this queue", messageQueue,
halfOffset, opOffset);
continue;
}
List<Long> doneOpOffset = new ArrayList<>();
HashMap<Long, Long> removeMap = new HashMap<>();
// 根据当前的处理进度 依次从已处理队列MQ_SYS_TRANS_OP_HALF_TOPIC拉取32条消息
PullResult pullResult = fillOpRemoveMap(removeMap, opQueue, opOffset, halfOffset, doneOpOffset);
if (null == pullResult) {
log.error("The queue={} check msgOffset={} with opOffset={} failed, pullResult is null",
messageQueue, halfOffset, opOffset);
continue;
}
// single thread
// 获取空消息的次数
int getMessageNullCount = 1;
// 当前处理半消息的进度
long newOffset = halfOffset;
// 当前处理消息的队列偏移量
long i = halfOffset;
while (true) {
// 超过时常等待下次调度
if (System.currentTimeMillis() - startTime > MAX_PROCESS_TIME_LIMIT) {
log.info("Queue={} process time reach max={}", messageQueue, MAX_PROCESS_TIME_LIMIT);
break;
}
// 如果该消息已被处理 继续处理下一条消息
if (removeMap.containsKey(i)) {
log.debug("Half offset {} has been committed/rolled back", i);
Long removedOpOffset = removeMap.remove(i);
doneOpOffset.add(removedOpOffset);
} else {
// 获取消息
GetResult getResult = getHalfMsg(messageQueue, i);
MessageExt msgExt = getResult.getMsg();
if (msgExt == null) {
// 超过重试次数 直接跳出 结束该消息队列的事务回查状态
if (getMessageNullCount++ > MAX_RETRY_COUNT_WHEN_HALF_NULL) {
break;
}
// 没有新的消息而返回 结束该消息队列的事务回查
if (getResult.getPullResult().getPullStatus() == PullStatus.NO_NEW_MSG) {
log.debug("No new msg, the miss offset={} in={}, continue check={}, pull result={}", i,
messageQueue, getMessageNullCount, getResult.getPullResult());
break;
} else {
log.info("Illegal offset, the miss offset={} in={}, continue check={}, pull result={}",
i, messageQueue, getMessageNullCount, getResult.getPullResult());
// 其它原因 重新拉取
i = getResult.getPullResult().getNextBeginOffset();
newOffset = i;
continue;
}
}
// needDiscard 如果该消息回查的次数超过允许回查的最大次数 该消息将被丢弃 事务消息提交失败 每回查一次 在消息属性中+1 默认回查最大次数为5
// needSkip 如果事务消息超过文件的过期时间 默认72小时 则跳过该消息
if (needDiscard(msgExt, transactionCheckMax) || needSkip(msgExt)) {
listener.resolveDiscardMsg(msgExt);
newOffset = i + 1;
i++;
continue;
}
if (msgExt.getStoreTimestamp() >= startTime) {
log.debug("Fresh stored. the miss offset={}, check it later, store={}", i,
new Date(msgExt.getStoreTimestamp()));
break;
}
// 消息已存储时间 当前系统时间减去消息存储时间
long valueOfCurrentMinusBorn = System.currentTimeMillis() - msgExt.getBornTimestamp();
// checkImmunityTime 立即检测事务消息的时间 设计的意义是 应用程序在发送事务消息后 事务不会马上提交 该时间就是假设事务消息发送成功后 应用程序事务提交时间 在这段时间内 RocketMQ任务事务未提交 不应该在这个时间段内向应用程序发送回查请求
// transactionTimeout 事务消息的超时时间 这个时间是从OP拉取消息的最后一条消息存储时间与check方法开始的时间 如果时间差超过了transactionTimeout 就算时间小于checkImmunityTime 也发送事务回查指令
long checkImmunityTime = transactionTimeout;
// PROPERTY_CHECK_IMMUNITY_TIME_IN_SECONDS 消息事务消息回查的最晚时间 单位为秒 指的是程序发送事务消息 可以指定该事务消息的有效时间 只有在这个时间内收到回查消息才有效 默认为null
String checkImmunityTimeStr = msgExt.getUserProperty(MessageConst.PROPERTY_CHECK_IMMUNITY_TIME_IN_SECONDS);
if (null != checkImmunityTimeStr) {
checkImmunityTime = getImmunityTime(checkImmunityTimeStr, transactionTimeout);
if (valueOfCurrentMinusBorn < checkImmunityTime) {
if (checkPrepareQueueOffset(removeMap, doneOpOffset, msgExt)) {
newOffset = i + 1;
i++;
continue;
}
}
} else {
// 如果当前时间没过应用程序事务结束时间 跳出本次处理
if ((0 <= valueOfCurrentMinusBorn) && (valueOfCurrentMinusBorn < checkImmunityTime)) {
log.debug("New arrived, the miss offset={}, check it later checkImmunity={}, born={}", i,
checkImmunityTime, new Date(msgExt.getBornTimestamp()));
break;
}
}
List<MessageExt> opMsg = pullResult.getMsgFoundList();
// 如果OP队列中没有已处理消息并且已经超过应用程序事务结束时间transactionTimeout
// 或者
// 操作队列不为空并且最后一条消息的存储时间已经超过transactionTimeout
boolean isNeedCheck = (opMsg == null && valueOfCurrentMinusBorn > checkImmunityTime)
|| (opMsg != null && (opMsg.get(opMsg.size() - 1).getBornTimestamp() - startTime > transactionTimeout))
|| (valueOfCurrentMinusBorn <= -1);
if (isNeedCheck) {
// 这里回查是异步处理的 所以在回查之前 需要把消息重新投递到队列中 以便下次check
if (!putBackHalfMsgQueue(msgExt, i)) {
continue;
}
// 执行回查逻辑
listener.resolveHalfMsg(msgExt);
} else {
// 如果无法判断是否发送回查消息 则加载更多的已处理消息进行筛选
pullResult = fillOpRemoveMap(removeMap, opQueue, pullResult.getNextBeginOffset(), halfOffset, doneOpOffset);
log.debug("The miss offset:{} in messageQueue:{} need to get more opMsg, result is:{}", i,
messageQueue, pullResult);
continue;
}
}
newOffset = i + 1;
i++;
}
if (newOffset != halfOffset) {
// 保存半消息的回查进度
transactionalMessageBridge.updateConsumeOffset(messageQueue, newOffset);
}
long newOpOffset = calculateOpOffset(doneOpOffset, opOffset);
if (newOpOffset != opOffset) {
// 保存OP进度
transactionalMessageBridge.updateConsumeOffset(opQueue, newOpOffset);
}
}
} catch (Throwable e) {
log.error("Check error", e);
}
}
7、Broker主动回查事务状态
public void resolveHalfMsg(final MessageExt msgExt) {
executorService.execute(new Runnable() {
@Override
public void run() {
try {
sendCheckMessage(msgExt);
} catch (Exception e) {
LOGGER.error("Send check message error!", e);
}
}
});
}
public void sendCheckMessage(MessageExt msgExt) throws Exception {
CheckTransactionStateRequestHeader checkTransactionStateRequestHeader = new CheckTransactionStateRequestHeader();
checkTransactionStateRequestHeader.setCommitLogOffset(msgExt.getCommitLogOffset());
checkTransactionStateRequestHeader.setOffsetMsgId(msgExt.getMsgId());
checkTransactionStateRequestHeader.setMsgId(msgExt.getUserProperty(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX));
checkTransactionStateRequestHeader.setTransactionId(checkTransactionStateRequestHeader.getMsgId());
checkTransactionStateRequestHeader.setTranStateTableOffset(msgExt.getQueueOffset());
msgExt.setTopic(msgExt.getUserProperty(MessageConst.PROPERTY_REAL_TOPIC));
msgExt.setQueueId(Integer.parseInt(msgExt.getUserProperty(MessageConst.PROPERTY_REAL_QUEUE_ID)));
msgExt.setStoreSize(0);
String groupId = msgExt.getProperty(MessageConst.PROPERTY_PRODUCER_GROUP);
// 从同一个生产者组中选择一个Producer进行回查
// 所以同一个生产者组中如果部分机器出现宕机、发布重启等问题 也不会影响回查
Channel channel = brokerController.getProducerManager().getAvailableChannel(groupId);
if (channel != null) {
brokerController.getBroker2Client().checkProducerTransactionState(groupId, channel, checkTransactionStateRequestHeader, msgExt);
} else {
LOGGER.warn("Check transaction failed, channel is null. groupId={}", groupId);
}
}
public void checkProducerTransactionState(
final String group,
final Channel channel,
final CheckTransactionStateRequestHeader requestHeader,
final MessageExt messageExt) throws Exception {
// 给Producer发送消息时 指定类型是CHECK_TRANSACTION_STATE
RemotingCommand request =
RemotingCommand.createRequestCommand(RequestCode.CHECK_TRANSACTION_STATE, requestHeader);
request.setBody(MessageDecoder.encode(messageExt, false));
try {
this.brokerController.getRemotingServer().invokeOneway(channel, request, 10);
} catch (Exception e) {
log.error("Check transaction failed because invoke producer exception. group={}, msgId={}, error={}",
group, messageExt.getMsgId(), e.toString());
}
}
9、Producer本地事务回查
public RemotingCommand processRequest(ChannelHandlerContext ctx,
RemotingCommand request) throws RemotingCommandException {
switch (request.getCode()) {
case RequestCode.CHECK_TRANSACTION_STATE:
// 判断是Broker事务回查 检查本地事务执行状态
return this.checkTransactionState(ctx, request);
// ......省略部分代码
}
return null;
}
public void checkTransactionState(final String addr, final MessageExt msg,
final CheckTransactionStateRequestHeader header) {
Runnable request = new Runnable() {
//...省略部分代码 下文解析
};
// 这里正是用新建TransactionMQProducer时创建的线程池异步执行提高效率
this.checkExecutor.submit(request);
}
public void run() {
TransactionCheckListener transactionCheckListener = DefaultMQProducerImpl.this.checkListener();
TransactionListener transactionListener = getCheckListener();
if (transactionCheckListener != null || transactionListener != null) {
LocalTransactionState localTransactionState = LocalTransactionState.UNKNOW;
Throwable exception = null;
try {
if (transactionCheckListener != null) {
localTransactionState = transactionCheckListener.checkLocalTransactionState(message);
} else if (transactionListener != null) {
// 检查本地事务
log.debug("Used new check API in transaction message");
localTransactionState = transactionListener.checkLocalTransaction(message);
} else {
log.warn("CheckTransactionState, pick transactionListener by group[{}] failed", group);
}
} catch (Throwable e) {
log.error("Broker call checkTransactionState, but checkLocalTransactionState exception", e);
exception = e;
}
// 将本地事务状态通知Broker
// 和第四步Producer第一次尝试通知Broker一样 也是单向发送 可能发送失败
this.processTransactionState(
localTransactionState,
group,
exception);
} else {
log.warn("CheckTransactionState, pick transactionCheckListener by group[{}] failed", group);
}
}