RocketMQ源碼解析：定時消息與消息重試
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1. 概述
建議前置閱讀內容：json
😈 爲何把定時消息與消息重試放在一塊兒？你猜。
👻 你猜我猜不猜。後端
2. 定時消息
定時消息是指消息發到 Broker 後，不能馬上被 Consumer 消費，要到特定的時間點或者等待特定的時間後才能被消費。微信
下圖是定時消息的處理邏輯圖：app
2.1 延遲級別
RocketMQ 目前只支持固定精度的定時消息。官方說法以下：ide
若是要支持任意的時間精度，在 Broker 層面，必需要作消息排序，若是再涉及到持久化，那麼消息排序要不可避免的產生巨大性能開銷。源碼分析
- 延遲級別：
| 延遲級別 | 時間 |
|---|---|
| 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 |
核心源碼以下：性能
1: // ⬇️⬇️⬇️【MessageStoreConfig.java】 2: /** 3: * 消息延遲級別字符串配置 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: * 解析延遲級別 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: }複製代碼
2.2 Producer 發送定時消息
- 🦅發送時，設置消息的延遲級別。
Message msg = new Message(...);
msg.setDelayTimeLevel(level);複製代碼
2.3 Broker 存儲定時消息
- 🦅 存儲消息時，延遲消息進入
Topic爲SCHEDULE_TOPIC_XXXX。 - 🦅 延遲級別 與 消息隊列編號 作固定映射：QueueId = DelayLevel - 1。
核心代碼以下：this
1: // ⬇️⬇️⬇️【CommitLog.java】
2: /** 3: * 添加消息，返回消息結果 4: * 5: * @param msg 消息 6: * @return 結果 7: */
8: public PutMessageResult putMessage(final MessageExtBrokerInner msg) {
9: // ....(省略代碼)
10:
11: // 定時消息處理
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: // 存儲消息時，延遲消息進入 `Topic` 爲 `SCHEDULE_TOPIC_XXXX` 。
22: topic = ScheduleMessageService.SCHEDULE_TOPIC;
23:
24: // 延遲級別 與 消息隊列編號 作固定映射
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: // ....(省略代碼)
38: }
39:
40: // ⬇️⬇️⬇️【ScheduleMessageService.java】
41: /** 42: * 根據 延遲級別 計算 消息隊列編號 43: * QueueId = DelayLevel - 1 44: * 45: * @param delayLevel 延遲級別 46: * @return 消息隊列編號 47: */
48: public static int delayLevel2QueueId(final int delayLevel) {
49: return delayLevel - 1;
50: }複製代碼
- 🦅 生成
ConsumeQueue時，每條消息的tagsCode使用【消息計劃消費時間】。這樣，ScheduleMessageService在輪詢ConsumeQueue時，能夠使用tagsCode進行過濾。
核心代碼以下：spa
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: // // ....(省略代碼)
10:
11: // 17 properties
12: short propertiesLength = byteBuffer.getShort();
13: if (propertiesLength > 0) {
14: // ....(省略代碼)
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: // ....(省略代碼)
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: * 計算 投遞時間【計劃消費時間】 62: * 63: * @param delayLevel 延遲級別 64: * @param storeTimestamp 存儲時間 65: * @return 投遞時間【計劃消費時間】 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: }複製代碼
2.4 Broker 發送定時消息
- 🦅 對
SCHEDULE_TOPIC_XXXX每條消費隊列對應單獨一個定時任務進行輪詢，發送 到達投遞時間【計劃消費時間】 的消息。
下圖是發送定時消息的處理邏輯圖：
實現代碼以下：
1: /** 2: * ⬇️⬇️⬇️ 發送（投遞）延遲消息定時任務 3: */
4: class DeliverDelayedMessageTimerTask extends TimerTask {
5: /** 6: * 延遲級別 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: * 糾正可投遞時間。 33: * 由於發送級別對應的發送間隔能夠調整，若是超過當前間隔，則修正成當前配置，避免後面的消息沒法發送。 34: * 35: * @param now 當前時間 36: * @param deliverTimestamp 投遞時間 37: * @return 糾正結果 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) { // 消息到達可發送時間
74: MessageExt msgExt = ScheduleMessageService.this.defaultMessageStore.lookMessageByOffset(offsetPy, sizePy);
75: if (msgExt != null) {
76: try {
77: // 發送消息
78: MessageExtBrokerInner msgInner = this.messageTimeup(msgExt);
79: PutMessageResult putMessageResult = ScheduleMessageService.this.defaultMessageStore.putMessage(msgInner);
80: if (putMessageResult != null && putMessageResult.getPutMessageStatus() == PutMessageStatus.PUT_OK) { // 發送成功
81: continue;
82: } else { // 發送失敗
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: // 安排下一次任務
87: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel, nextOffset), DELAY_FOR_A_PERIOD);
88:
89: // 更新進度
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: // 安排下一次任務
101: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel, nextOffset), countdown);
102:
103: // 更新進度
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: // 安排下一次任務
112: ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel, nextOffset), DELAY_FOR_A_WHILE);
113:
114: // 更新進度
115: ScheduleMessageService.this.updateOffset(this.delayLevel, nextOffset);
116: return;
117: } finally {
118: bufferCQ.release();
119: }
120: } // end of if (bufferCQ != null)
121: else { // 消費隊列已經被刪除部分，跳轉到最小的消費進度
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: * 設置消息內容 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: }複製代碼
2.5 Broker 持久化定時發送進度
- 🦅 定時消息發送進度存儲在文件(
../config/delayOffset.json)裏 - 🦅 每 10s 定時持久化發送進度。
核心代碼以下：
1: // ⬇️⬇️⬇️【ScheduleMessageService.java】
2: /** 3: public void start() { 4: // 定時發送消息 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: // 定時持久化發送進度 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: }複製代碼
3. 消息重試
Consumer 消費消息失敗後，要提供一種重試機制，令消息再消費一次。
- 🦅
Consumer將消費失敗的消息發回Broker，進入延遲消息隊列。即，消費失敗的消息，不會當即消費。
核心代碼以下：
1: // ⬇️⬇️⬇️【SendMessageProcessor.java】
2: /** 3: * 消費者發回消息 4: * 5: * @param ctx ctx 6: * @param request 請求 7: * @return 響應 8: * @throws RemotingCommandException 當遠程調用異常 9: */
10: private RemotingCommand consumerSendMsgBack(final ChannelHandlerContext ctx, final RemotingCommand request) 11: throws RemotingCommandException {
12: // ....(省略代碼)
13: // 處理 delayLevel（獨有）。
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: // ....(省略代碼)
21: } else {
22: if (0 == delayLevel) {
23: delayLevel = 3 + msgExt.getReconsumeTimes();
24: }
25: msgExt.setDelayTimeLevel(delayLevel);
26: }
27:
28: // ....(省略代碼)
29: return response;
30: }複製代碼
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