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本文主要基于 RocketMQ 4.0.x 正式版
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1. 概述
建议前置阅读内容：
😈 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：
| 延迟级别 | 时间 |
|---|---|
| 1 | 1s |
| 2 | 5s |
| 3 | 10s |
| 4 | 30s |
| 5 | 1m |
| 6 | 2m |
| 7 | 3m |
| 8 | 4m |
| 9 | 5m |
| 10 | 6m |
| 11 | 7m |
| 12 | 8m |
| 13 | 9m |
| 14 | 10m |
| 15 | 20m |
| 16 | 30m |
| 17 | 1h |
| 18 | 2h |
-
核心源码如下：
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 for
108:
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: }
666. 彩蛋
来源：oschina
链接：https://my.oschina.net/u/210730/blog/900652