基础概念
- RocketMQ的架构部署与模型概念
实现原理-重点
核心流程
- producer端 设置消息的延迟级别与属性
- broker端 收到消息根据标记会 修改消息的 topic 名称（SCHEDULE_TOPIC_XXXX）和转发消息到延迟主题的 ConsumeQueue 中
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- 会启动一个定时任务 每隔1s拉取需要投递的延迟消息
- 将消息重新存储到 commitlog 中
- 将消息投递到目标 topic 中
- consumer端 正常消息
源码
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延时消息等级
// 18个延时消息等级 org.apache.rocketmq.store.config.MessageStoreConfig#messageDelayLevel
private String messageDelayLevel = "1s 5s 10s 30s 1m 2m 3m 4m 5m 6m 7m 8m 9m 10m 20m 30m 1h 2h";
// 开源版是秒级，不精确的
org.apache.rocketmq.store.schedule.ScheduleMessageService.DeliverDelayedMessageTimerTask#run
// 代码入口
org.apache.rocketmq.store.schedule.ScheduleMessageService#load
// 大致就是将18个时间等级解析为毫秒 然后存入delayLevelTable，即初始化延时级别与对应延迟时间的映射关系
public boolean parseDelayLevel() {
// 秒分时天 转为毫秒
HashMap<String, Long> timeUnitTable = new HashMap<String, Long>();
timeUnitTable.put("s", 1000L);
timeUnitTable.put("m", 1000L * 60);
timeUnitTable.put("h", 1000L * 60 * 60);
timeUnitTable.put("d", 1000L * 60 * 60 * 24);
String levelString = this.defaultMessageStore.getMessageStoreConfig().getMessageDelayLevel();
try {
String[] levelArray = levelString.split(" ");
for (int i = 0; i < levelArray.length; i++) {
String value = levelArray[i];
String ch = value.substring(value.length() - 1);
Long tu = timeUnitTable.get(ch);
int level = i + 1;
if (level > this.maxDelayLevel) {
this.maxDelayLevel = level;
}
long num = Long.parseLong(value.substring(0, value.length() - 1));
long delayTimeMillis = tu * num;
this.delayLevelTable.put(level, delayTimeMillis);
}
} catch (Exception e) {
log.error("parseDelayLevel exception", e);
log.info("levelString String = {}", levelString);
return false;
}
return true;
}
org.apache.rocketmq.store.CommitLog#asyncPutMessage
1.将topic设置为 RMQ_SYS_SCHEDULE_TOPIC
2.将实际的topic和queue 找地方存着，后续替换使用
// 代码入口
org.apache.rocketmq.store.schedule.ScheduleMessageService#start
// Broker为每个时间等级 创建一个timer定时任务，共18个
public void start() {
if (started.compareAndSet(false, true)) {
super.load();
this.timer = new Timer("ScheduleMessageTimerThread", true);
for (Map.Entry<Integer, Long> entry : this.delayLevelTable.entrySet()) {
Integer level = entry.getKey();
Long timeDelay = entry.getValue();
Long offset = this.offsetTable.get(level);
if (null == offset) {
offset = 0L;
}
if (timeDelay != null) {
this.timer.schedule(new DeliverDelayedMessageTimerTask(level, offset), FIRST_DELAY_TIME);
}
}
this.timer.scheduleAtFixedRate(new TimerTask() {
@Override
public void run() {
try {
if (started.get()) {
ScheduleMessageService.this.persist();
}
} catch (Throwable e) {
log.error("scheduleAtFixedRate flush exception", e);
}
}
}, 10000, this.defaultMessageStore.getMessageStoreConfig().getFlushDelayOffsetInterval());
}
}
// 代码入口
org.apache.rocketmq.store.schedule.ScheduleMessageService.DeliverDelayedMessageTimerTask#executeOnTimeup
public void executeOnTimeup() {
ConsumeQueue cq =
// 根据topic和延迟的level找具体消费的队列
ScheduleMessageService.this.defaultMessageStore.findConsumeQueue(TopicValidator.RMQ_SYS_SCHEDULE_TOPIC,
delayLevel2QueueId(delayLevel));
long failScheduleOffset = offset;
if (cq != null) {
// 根据偏移量获取 队列的消息
SelectMappedBufferResult bufferCQ = cq.getIndexBuffer(this.offset);
if (bufferCQ != null) {
try {
long nextOffset = offset;
int i = 0;
ConsumeQueueExt.CqExtUnit cqExtUnit = new ConsumeQueueExt.CqExtUnit();
// 循环处理消息
for (; i < bufferCQ.getSize(); i += ConsumeQueue.CQ_STORE_UNIT_SIZE) {
long offsetPy = bufferCQ.getByteBuffer().getLong();
int sizePy = bufferCQ.getByteBuffer().getInt();
long tagsCode = bufferCQ.getByteBuffer().getLong();
if (cq.isExtAddr(tagsCode)) {
if (cq.getExt(tagsCode, cqExtUnit)) {
tagsCode = cqExtUnit.getTagsCode();
} else {
//can't find ext content.So re compute tags code.
log.error("[BUG] can't find consume queue extend file content!addr={}, offsetPy={}, sizePy={}",
tagsCode, offsetPy, sizePy);
long msgStoreTime = defaultMessageStore.getCommitLog().pickupStoreTimestamp(offsetPy, sizePy);
tagsCode = computeDeliverTimestamp(delayLevel, msgStoreTime);
}
}
long now = System.currentTimeMillis();
// 消息投递到中间件的时间
long deliverTimestamp = this.correctDeliverTimestamp(now, tagsCode);
nextOffset = offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE);
// 计算消息是否需要马上投递
long countdown = deliverTimestamp - now;
if (countdown <= 0) {
MessageExt msgExt =
ScheduleMessageService.this.defaultMessageStore.lookMessageByOffset(
offsetPy, sizePy);
if (msgExt != null) {
try {
// 组装真正的topic消息
MessageExtBrokerInner msgInner = this.messageTimeup(msgExt);
if (TopicValidator.RMQ_SYS_TRANS_HALF_TOPIC.equals(msgInner.getTopic())) {
log.error("[BUG] the real topic of schedule msg is {}, discard the msg. msg={}",
msgInner.getTopic(), msgInner);
continue;
}
// 写入到commitlog中，投入到真正的队列里面
PutMessageResult putMessageResult =
ScheduleMessageService.this.writeMessageStore
.putMessage(msgInner);
if (putMessageResult != null
&& putMessageResult.getPutMessageStatus() == PutMessageStatus.PUT_OK) {
if (ScheduleMessageService.this.defaultMessageStore.getMessageStoreConfig().isEnableScheduleMessageStats()) {
ScheduleMessageService.this.defaultMessageStore.getBrokerStatsManager().incQueueGetNums(MixAll.SCHEDULE_CONSUMER_GROUP, TopicValidator.RMQ_SYS_SCHEDULE_TOPIC, delayLevel - 1, putMessageResult.getAppendMessageResult().getMsgNum());
ScheduleMessageService.this.defaultMessageStore.getBrokerStatsManager().incQueueGetSize(MixAll.SCHEDULE_CONSUMER_GROUP, TopicValidator.RMQ_SYS_SCHEDULE_TOPIC, delayLevel - 1, putMessageResult.getAppendMessageResult().getWroteBytes());
ScheduleMessageService.this.defaultMessageStore.getBrokerStatsManager().incGroupGetNums(MixAll.SCHEDULE_CONSUMER_GROUP, TopicValidator.RMQ_SYS_SCHEDULE_TOPIC, putMessageResult.getAppendMessageResult().getMsgNum());
ScheduleMessageService.this.defaultMessageStore.getBrokerStatsManager().incGroupGetSize(MixAll.SCHEDULE_CONSUMER_GROUP, TopicValidator.RMQ_SYS_SCHEDULE_TOPIC, putMessageResult.getAppendMessageResult().getWroteBytes());
ScheduleMessageService.this.defaultMessageStore.getBrokerStatsManager().incTopicPutNums(msgInner.getTopic(), putMessageResult.getAppendMessageResult().getMsgNum(), 1);
ScheduleMessageService.this.defaultMessageStore.getBrokerStatsManager().incTopicPutSize(msgInner.getTopic(),
putMessageResult.getAppendMessageResult().getWroteBytes());
ScheduleMessageService.this.defaultMessageStore.getBrokerStatsManager().incBrokerPutNums(putMessageResult.getAppendMessageResult().getMsgNum());
}
continue;
} else {
// XXX: warn and notify me
log.error(
"ScheduleMessageService, a message time up, but reput it failed, topic: {} msgId {}",
msgExt.getTopic(), msgExt.getMsgId());
ScheduleMessageService.this.timer.schedule(
new DeliverDelayedMessageTimerTask(this.delayLevel,
nextOffset), DELAY_FOR_A_PERIOD);
ScheduleMessageService.this.updateOffset(this.delayLevel,
nextOffset);
return;
}
} catch (Exception e) {
/*
* XXX: warn and notify me
*/
log.error(
"ScheduleMessageService, messageTimeup execute error, drop it. msgExt={}, nextOffset={}, offsetPy={}, sizePy={}", msgExt, nextOffset, offsetPy, sizePy, e);
}
}
} else {
// 新建定时任务
ScheduleMessageService.this.timer.schedule(
new DeliverDelayedMessageTimerTask(this.delayLevel, nextOffset),
countdown);
ScheduleMessageService.this.updateOffset(this.delayLevel, nextOffset);
return;
}
} // end of for
nextOffset = offset + (i / ConsumeQueue.CQ_STORE_UNIT_SIZE);
ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(
this.delayLevel, nextOffset), DELAY_FOR_A_WHILE);
ScheduleMessageService.this.updateOffset(this.delayLevel, nextOffset);
return;
} finally {
bufferCQ.release();
}
} // end of if (bufferCQ != null)
else {
// 更新下次需要扫描的偏移量
long cqMinOffset = cq.getMinOffsetInQueue();
long cqMaxOffset = cq.getMaxOffsetInQueue();
if (offset < cqMinOffset) {
failScheduleOffset = cqMinOffset;
log.error("schedule CQ offset invalid. offset={}, cqMinOffset={}, cqMaxOffset={}, queueId={}",
offset, cqMinOffset, cqMaxOffset, cq.getQueueId());
}
if (offset > cqMaxOffset) {
failScheduleOffset = cqMaxOffset;
log.error("schedule CQ offset invalid. offset={}, cqMinOffset={}, cqMaxOffset={}, queueId={}",
offset, cqMinOffset, cqMaxOffset, cq.getQueueId());
}
}
} // end of if (cq != null)
ScheduleMessageService.this.timer.schedule(new DeliverDelayedMessageTimerTask(this.delayLevel,
failScheduleOffset), DELAY_FOR_A_WHILE);
}
//
消除消息的延时属性-->获取消息原始topic-->获取消息原始queueId
private MessageExtBrokerInner messageTimeup(MessageExt msgExt) {
MessageExtBrokerInner msgInner = new MessageExtBrokerInner();
msgInner.setBody(msgExt.getBody());
msgInner.setFlag(msgExt.getFlag());
MessageAccessor.setProperties(msgInner, msgExt.getProperties());
TopicFilterType topicFilterType = MessageExt.parseTopicFilterType(msgInner.getSysFlag());
long tagsCodeValue =
MessageExtBrokerInner.tagsString2tagsCode(topicFilterType, msgInner.getTags());
msgInner.setTagsCode(tagsCodeValue);
msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgExt.getProperties()));
msgInner.setSysFlag(msgExt.getSysFlag());
msgInner.setBornTimestamp(msgExt.getBornTimestamp());
msgInner.setBornHost(msgExt.getBornHost());
msgInner.setStoreHost(msgExt.getStoreHost());
msgInner.setReconsumeTimes(msgExt.getReconsumeTimes());
msgInner.setWaitStoreMsgOK(false);
MessageAccessor.clearProperty(msgInner, MessageConst.PROPERTY_DELAY_TIME_LEVEL);
msgInner.setTopic(msgInner.getProperty(MessageConst.PROPERTY_REAL_TOPIC));
String queueIdStr = msgInner.getProperty(MessageConst.PROPERTY_REAL_QUEUE_ID);
int queueId = Integer.parseInt(queueIdStr);
msgInner.setQueueId(queueId);
return msgInner;
}
小结
- 简单介绍了 RocketMQ 部署架构、模型
- 开源版本有18个延时等级，不可随意指定，也并不是精准延时，内部会建18个延时任务分别扫描各自级别的一个消息逻辑；商业版更加精准
- 在发送消息时可以指定等级，消息到达broker后会替换为 SCHEDULE_TOPIC_XXXX，真实的topic存在properties中，根据offset取出有消息则替换，放入正确的队列中进行消费
- 消费失败重试16次也是基于延时消息实现的，只是把前面两个level去掉了
- 优缺点
- 优点：设计简单，定时扫描，想通的延时消息都放在一个队列中，可以保证消息的顺序性
- 缺点：单线程，消息量太大会导致到期消息也无法消费的情况出现（即没二次发送出来）
其他MQ产品延时消息的实现
- DDMQ
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底层消息中间件的基础上加了一层代理，独立部署延迟服务模块，使用rocksdb进行临时存储。rocksdb是一个高性能的KV存储，并支持排序
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