RocketMQ源码解析：定时消息与消息重试
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title: RocketMQ 源码分析 —— 定时消息与消息重试
date: 2017-05-15
tags:
categories: RocketMQ
permalink: RocketMQ/message-schedule-and-retry
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- 1. 概述
- 2. 定时消息
- 2.1 延迟级别
- 2.2 Producer 发送定时消息
- 2.3 Broker 存储定时消息
- 2.4 Broker 发送定时消息
- 2.5 Broker 持久化定时发送进度
- 3. 消息重试
1. 概述
建议前置阅读内容：
- 《RocketMQ 源码分析 —— Message 发送与接收》
- 《RocketMQ 源码分析 —— Message 拉取与消费（下）》
�� 为什么把定时消息与消息重试放在一起？你猜。
�� 你猜我猜不猜。
2. 定时消息
定时消息是指消息发到 Broker 后，不能立刻被 Consumer 消费，要到特定的时间点或者等待特定的时间后才能被消费。
下图是定时消息的处理逻辑图：
2.1 延迟级别
RocketMQ 目前只支持固定精度的定时消息。官方说法如下：
如果要支持任意的时间精度，在 Broker 层面，必须要做消息排序，如果再涉及到持久化，那么消息排序要不可避免的产生巨大性能开销。
- 延迟级别：
* 核心源码如下：
```Java 1: // ⬇️⬇️⬇️【MessageStoreConfig.java】 2: /** 3: * 消息延迟级别字符串配置 4: */ 5: private String messageDelayLevel = "1s 5s 10s 30s 1m 2m 3m 4m 5m 6m 7m 8m 9m 10m 20m 30m 1h 2h"; 6: 7: // ⬇️⬇️⬇️【ScheduleMessageService.java】 8: /** 9: * 解析延迟级别 10: * 11: * @return 是否解析成功 12: */ 13: public boolean parseDelayLevel() { 14: HashMap<String, Long> timeUnitTable = new HashMap<>(); 15: timeUnitTable.put("s", 1000L); 16: timeUnitTable.put("m", 1000L * 60); 17: timeUnitTable.put("h", 1000L * 60 * 60); 18: timeUnitTable.put("d", 1000L * 60 * 60 * 24); 19: 20: String levelString = this.defaultMessageStore.getMessageStoreConfig().getMessageDelayLevel(); 21: try { 22: String[] levelArray = levelString.split(" "); 23: for (int i = 0; i < levelArray.length; i++) { 24: String value = levelArray[i]; 25: String ch = value.substring(value.length() - 1); 26: Long tu = timeUnitTable.get(ch); 27: 28: int level = i + 1; 29: if (level > this.maxDelayLevel) { 30: this.maxDelayLevel = level; 31: } 32: long num = Long.parseLong(value.substring(0, value.length() - 1)); 33: long delayTimeMillis = tu * num; 34: this.delayLevelTable.put(level, delayTimeMillis); 35: } 36: } catch (Exception e) { 37: log.error("parseDelayLevel exception", e); 38: log.info("levelString String = {}", levelString); 39: return false; 40: } 41: 42: return true; 43: }```2.2 Producer 发送定时消息
- ��发送时，设置消息的延迟级别。
Message msg = new Message(...);msg.setDelayTimeLevel(level);2.3 Broker 存储定时消息
- �� 存储消息时，延迟消息进入
Topic为SCHEDULE_TOPIC_XXXX。 - �� 延迟级别 与 消息队列编号 做固定映射：QueueId = DelayLevel - 1。
核心代码如下：
1: // ⬇️⬇️⬇️【CommitLog.java】 2: /** 3: * 添加消息，返回消息结果 4: * 5: * @param msg 消息 6: * @return 结果 7: */ 8: public PutMessageResult putMessage(final MessageExtBrokerInner msg) { 9: // ....(省略代码) 10: 11: // 定时消息处理 12: final int tranType = MessageSysFlag.getTransactionValue(msg.getSysFlag()); 13: if (tranType == MessageSysFlag.TRANSACTION_NOT_TYPE// 14: || tranType == MessageSysFlag.TRANSACTION_COMMIT_TYPE) { 15: // Delay Delivery 16: if (msg.getDelayTimeLevel() > 0) { 17: if (msg.getDelayTimeLevel() > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) { 18: msg.setDelayTimeLevel(this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()); 19: } 20: 21: // 存储消息时，延迟消息进入 `Topic` 为 `SCHEDULE_TOPIC_XXXX` 。 22: topic = ScheduleMessageService.SCHEDULE_TOPIC; 23: 24: // 延迟级别 与 消息队列编号 做固定映射 25: queueId = ScheduleMessageService.delayLevel2QueueId(msg.getDelayTimeLevel()); 26: 27: // Backup real topic, queueId 28: MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_TOPIC, msg.getTopic()); 29: MessageAccessor.putProperty(msg, MessageConst.PROPERTY_REAL_QUEUE_ID, String.valueOf(msg.getQueueId())); 30: msg.setPropertiesString(MessageDecoder.messageProperties2String(msg.getProperties())); 31: 32: msg.setTopic(topic); 33: msg.setQueueId(queueId); 34: } 35: } 36: 37: // ....(省略代码) 38: } 39: 40: // ⬇️⬇️⬇️【ScheduleMessageService.java】 41: /** 42: * 根据 延迟级别 计算 消息队列编号 43: * QueueId = DelayLevel - 1 44: * 45: * @param delayLevel 延迟级别 46: * @return 消息队列编号 47: */ 48: public static int delayLevel2QueueId(final int delayLevel) { 49: return delayLevel - 1; 50: }- �� 生成
ConsumeQueue时，每条消息的tagsCode使用【消息计划消费时间】。这样，ScheduleMessageService在轮询ConsumeQueue时，可以使用tagsCode进行过滤。
核心代码如下：
1: // ⬇️⬇️⬇️【CommitLog.java】 2: /** 3: * check the message and returns the message size 4: * 5: * @return 0 Come the end of the file // >0 Normal messages // -1 Message checksum failure 6: */ 7: public DispatchRequest checkMessageAndReturnSize(ByteBuffer byteBuffer, final boolean checkCRC, final boolean readBody) { 8: try { 9: // // ....(省略代码) 10: 11: // 17 properties 12: short propertiesLength = byteBuffer.getShort(); 13: if (propertiesLength > 0) { 14: // ....(省略代码) 15: String tags = propertiesMap.get(MessageConst.PROPERTY_TAGS); 16: if (tags != null && tags.length() > 0) { 17: tagsCode = MessageExtBrokerInner.tagsString2tagsCode(MessageExt.parseTopicFilterType(sysFlag), tags); 18: } 19: 20: // Timing message processing 21: { 22: String t = propertiesMap.get(MessageConst.PROPERTY_DELAY_TIME_LEVEL); 23: if (ScheduleMessageService.SCHEDULE_TOPIC.equals(topic) && t != null) { 24: int delayLevel = Integer.parseInt(t); 25: 26: if (delayLevel > this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel()) { 27: delayLevel = this.defaultMessageStore.getScheduleMessageService().getMaxDelayLevel(); 28: } 29: 30: if (delayLevel > 0) { 31: tagsCode = this.defaultMessageStore.getScheduleMessageService().computeDeliverTimestamp(delayLevel, 32: storeTimestamp); 33: } 34: } 35: } 36: } 37: 38: // ....(省略代码) 39: 40: return new DispatchRequest(// 41: topic, // 1 42: queueId, // 2 43: physicOffset, // 3 44: totalSize, // 4 45: tagsCode, // 5 46: storeTimestamp, // 6 47: queueOffset, // 7 48: keys, // 8 49: uniqKey, //9 50: sysFlag, // 9 51: preparedTransactionOffset// 10 52: ); 53: } catch (Exception e) { 54: } 55: 56: return new DispatchRequest(-1, false /* success */); 57: } 58: 59: // ⬇️⬇️⬇️【ScheduleMessageService.java】 60: /** 61: * 计算 投递时间【计划消费时间】 62: * 63: * @param delayLevel 延迟级别 64: * @param storeTimestamp 存储时间 65: * @return 投递时间【计划消费时间】 66: */ 67: public long computeDeliverTimestamp(final int delayLevel, final long storeTimestamp) { 68: Long time = this.delayLevelTable.get(delayLevel); 69: if (time != null) { 70: return time + storeTimestamp; 71: } 72: 73: return storeTimestamp + 1000; 74: }2.4 Broker 发送定时消息
- �� 对
SCHEDULE_TOPIC_XXXX每条消费队列对应单独一个定时任务进行轮询，发送 到达投递时间【计划消费时间】 的消息。
下图是发送定时消息的处理逻辑图：
实现代码如下：
1: /** 2: * ⬇️⬇️⬇️ 发送（投递）延迟消息定时任务 3: */ 4: class DeliverDelayedMessageTimerTask extends TimerTask { 5: /** 6: * 延迟级别 7: */ 8: private final int delayLevel; 9: /** 10: * 位置 11: */ 12: private final long offset; 13: 14: public DeliverDelayedMessageTimerTask(int delayLevel, long offset) { 15: this.delayLevel = delayLevel; 16: this.offset = offset; 17: } 18: 19: @Override 20: public void run() { 21: try { 22: this.executeOnTimeup(); 23: } catch (Exception e) { 24: // XXX: warn and notify me 25: log.error("ScheduleMessageService, executeOnTimeup exception", e); 26: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask( 27: this.delayLevel, this.offset), DELAY_FOR_A_PERIOD); 28: } 29: } 30: 31: /** 32: * 纠正可投递时间。 33: * 因为发送级别对应的发送间隔可以调整，如果超过当前间隔，则修正成当前配置，避免后面的消息无法发送。 34: * 35: * @param now 当前时间 36: * @param deliverTimestamp 投递时间 37: * @return 纠正结果 38: */ 39: private long correctDeliverTimestamp(final long now, final long deliverTimestamp) { 40: long result = deliverTimestamp; 41: 42: long maxTimestamp = now + ScheduleMessageService.this.delayLevelTable.get(this.delayLevel); 43: if (deliverTimestamp > maxTimestamp) { 44: result = now; 45: } 46: 47: return result; 48: } 49: 50: public void executeOnTimeup() { 51: ConsumeQueue cq = ScheduleMessageService.this.defaultMessageStore.findConsumeQueue(SCHEDULE_TOPIC, delayLevel2QueueId(delayLevel)); 52: 53: long failScheduleOffset = offset; 54: 55: if (cq != null) { 56: SelectMappedBufferResult bufferCQ = cq.getIndexBuffer(this.offset); 57: if (bufferCQ != null) { 58: try { 59: long nextOffset = offset; 60: int i = 0; 61: for (; i < bufferCQ.getSize(); i += ConsumeQueue.CQ_STORE_UNIT_SIZE) { 62: long offsetPy = bufferCQ.getByteBuffer().getLong(); 63: int sizePy = bufferCQ.getByteBuffer().getInt(); 64: long tagsCode = bufferCQ.getByteBuffer().getLong(); 65: 66: long now = System.currentTimeMillis(); 67: long deliverTimestamp = this.correctDeliverTimestamp(now, tagsCode); 68: 69: nextOffset = offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE); 70: 71: long countdown = deliverTimestamp - now; 72: 73: if (countdown <= 0) { // 消息到达可发送时间 74: MessageExt msgExt = ScheduleMessageService.this.defaultMessageStore.lookMessageByOffset(offsetPy, sizePy); 75: if (msgExt != null) { 76: try { 77: // 发送消息 78: MessageExtBrokerInner msgInner = this.messageTimeup(msgExt); 79: PutMessageResult putMessageResult = ScheduleMessageService.this.defaultMessageStore.putMessage(msgInner); 80: if (putMessageResult != null && putMessageResult.getPutMessageStatus() == PutMessageStatus.PUT_OK) { // 发送成功 81: continue; 82: } else { // 发送失败 83: // XXX: warn and notify me 84: log.error("ScheduleMessageService, a message time up, but reput it failed, topic: {} msgId {}", msgExt.getTopic(), msgExt.getMsgId()); 85: 86: // 安排下一次任务 87: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel, nextOffset), DELAY_FOR_A_PERIOD); 88: 89: // 更新进度 90: ScheduleMessageService.this.updateOffset(this.delayLevel, nextOffset); 91: return; 92: } 93: } catch (Exception e) { 94: // XXX: warn and notify me 95: log.error("ScheduleMessageService, messageTimeup execute error, drop it. msgExt=" 96: + msgExt + ", nextOffset=" + nextOffset + ",offsetPy=" + offsetPy + ",sizePy=" + sizePy, e); 97: } 98: } 99: } else {100: // 安排下一次任务101: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel, nextOffset), countdown);102: 103: // 更新进度104: ScheduleMessageService.this.updateOffset(this.delayLevel, nextOffset);105: return;106: }107: } // end of for108: 109: nextOffset = offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE);110: 111: // 安排下一次任务112: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel, nextOffset), DELAY_FOR_A_WHILE);113: 114: // 更新进度115: ScheduleMessageService.this.updateOffset(this.delayLevel, nextOffset);116: return;117: } finally {118: bufferCQ.release();119: }120: } // end of if (bufferCQ != null)121: else { // 消费队列已经被删除部分，跳转到最小的消费进度122: long cqMinOffset = cq.getMinOffsetInQueue();123: if (offset < cqMinOffset) {124: failScheduleOffset = cqMinOffset;125: log.error("schedule CQ offset invalid. offset=" + offset + ", cqMinOffset="126: + cqMinOffset + ", queueId=" + cq.getQueueId());127: }128: }129: } // end of if (cq != null)130: 131: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel, failScheduleOffset), DELAY_FOR_A_WHILE);132: }133: 134: /**135: * 设置消息内容136: *137: * @param msgExt 消息138: * @return 消息139: */140: private MessageExtBrokerInner messageTimeup(MessageExt msgExt) {141: MessageExtBrokerInner msgInner = new MessageExtBrokerInner();142: msgInner.setBody(msgExt.getBody());143: msgInner.setFlag(msgExt.getFlag());144: MessageAccessor.setProperties(msgInner, msgExt.getProperties());145: 146: TopicFilterType topicFilterType = MessageExt.parseTopicFilterType(msgInner.getSysFlag());147: long tagsCodeValue =148: MessageExtBrokerInner.tagsString2tagsCode(topicFilterType, msgInner.getTags());149: msgInner.setTagsCode(tagsCodeValue);150: msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgExt.getProperties()));151: 152: msgInner.setSysFlag(msgExt.getSysFlag());153: msgInner.setBornTimestamp(msgExt.getBornTimestamp());154: msgInner.setBornHost(msgExt.getBornHost());155: msgInner.setStoreHost(msgExt.getStoreHost());156: msgInner.setReconsumeTimes(msgExt.getReconsumeTimes());157: 158: msgInner.setWaitStoreMsgOK(false);159: MessageAccessor.clearProperty(msgInner, MessageConst.PROPERTY_DELAY_TIME_LEVEL);160: 161: msgInner.setTopic(msgInner.getProperty(MessageConst.PROPERTY_REAL_TOPIC));162: 163: String queueIdStr = msgInner.getProperty(MessageConst.PROPERTY_REAL_QUEUE_ID);164: int queueId = Integer.parseInt(queueIdStr);165: msgInner.setQueueId(queueId);166: 167: return msgInner;168: }169: }2.5 Broker 持久化定时发送进度
- �� 定时消息发送进度存储在文件(
../config/delayOffset.json)里 - �� 每 10s 定时持久化发送进度。
核心代码如下：
1: // ⬇️⬇️⬇️【ScheduleMessageService.java】 2: /** 3: public void start() { 4: // 定时发送消息 5: for (Map.Entry<Integer, Long> entry : this.delayLevelTable.entrySet()) { 6: Integer level = entry.getKey(); 7: Long timeDelay = entry.getValue(); 8: Long offset = this.offsetTable.get(level); 9: if (null == offset) { 10: offset = 0L; 11: } 12: 13: if (timeDelay != null) { 14: this.timer.schedule(new DeliverDelayedMessageTimerTask(level, offset), FIRST_DELAY_TIME); 15: } 16: } 17: 18: // 定时持久化发送进度 19: this.timer.scheduleAtFixedRate(new TimerTask() { 20: 21: @Override 22: public void run() { 23: try { 24: ScheduleMessageService.this.persist(); 25: } catch (Exception e) { 26: log.error("scheduleAtFixedRate flush exception", e); 27: } 28: } 29: }, 10000, this.defaultMessageStore.getMessageStoreConfig().getFlushDelayOffsetInterval()); 30: }3. 消息重试
Consumer 消费消息失败后，要提供一种重试机制，令消息再消费一次。
- ��
Consumer将消费失败的消息发回Broker，进入延迟消息队列。即，消费失败的消息，不会立即消费。
核心代码如下：
1: // ⬇️⬇️⬇️【SendMessageProcessor.java】 2: /** 3: * 消费者发回消息 4: * 5: * @param ctx ctx 6: * @param request 请求 7: * @return 响应 8: * @throws RemotingCommandException 当远程调用异常 9: */ 10: private RemotingCommand consumerSendMsgBack(final ChannelHandlerContext ctx, final RemotingCommand request) 11: throws RemotingCommandException { 12: // ....(省略代码) 13: // 处理 delayLevel（独有）。 14: int delayLevel = requestHeader.getDelayLevel(); 15: int maxReconsumeTimes = subscriptionGroupConfig.getRetryMaxTimes(); 16: if (request.getVersion() >= MQVersion.Version.V3_4_9.ordinal()) { 17: maxReconsumeTimes = requestHeader.getMaxReconsumeTimes(); 18: } 19: if (msgExt.getReconsumeTimes() >= maxReconsumeTimes// 20: // ....(省略代码) 21: } else { 22: if (0 == delayLevel) { 23: delayLevel = 3 + msgExt.getReconsumeTimes(); 24: } 25: msgExt.setDelayTimeLevel(delayLevel); 26: } 27: 28: // ....(省略代码) 29: return response; 30: }阅读全文
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