RocketMQ(4.8.0)——生产者
RocketMQ(4.8.0)——生产者
一、生产者概述
发送消息的一方被称为生产者，它在整个RocketMQ的生产者和消费体中扮演角色如下：
基本概念：
生产者组： 一个逻辑概念，在使用生产者实例的时候需要制定一个组名。一个生产者组可以生产多个Topic的消息。
生产者实例：一个生产者组部署了多个进程，每个进程都可以称为一个生产者实例。
Topic：主题名字，一个Topic由若干Queue组成。
RocketMQ 客户端中的生产者有两个独立实现类：org.apache.rocketmq.client.producer.defaultmqproducer(普通消息、顺序消息、单向消息、批量消息、延迟消息) 和 org.apache.rocketmq.client.producer.transactionmqproducer(事务消息)。
二、消息结构和消息类型
rocketmq-master/common/src/main/java/org/apache/rocketmq/common/message/Message.java (rocketmq-all-4.8.0)
1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.rocketmq.common.message;
18
19 import java.io.Serializable;
20 import java.util.Arrays;
21 import java.util.Collection;
22 import java.util.HashMap;
23 import java.util.Map;
24
25 public class Message implements Serializable {
26 private static final long serialVersionUID = 8445773977080406428L;
27
28 private String topic;
29 private int flag;
30 private Map<String, String> properties;
31 private byte[] body;
32 private String transactionId;
33
34 public Message() {
35 }
36
37 public Message(String topic, byte[] body) {
38 this(topic, "", "", 0, body, true);
39 }
40
41 public Message(String topic, String tags, String keys, int flag, byte[] body, boolean waitStoreMsgOK) {
42 this.topic = topic;
43 this.flag = flag;
44 this.body = body;
45
46 if (tags != null && tags.length() > 0)
47 this.setTags(tags);
48
49 if (keys != null && keys.length() > 0)
50 this.setKeys(keys);
51
52 this.setWaitStoreMsgOK(waitStoreMsgOK);
53 }
54
55 public Message(String topic, String tags, byte[] body) {
56 this(topic, tags, "", 0, body, true);
57 }
58
59 public Message(String topic, String tags, String keys, byte[] body) {
60 this(topic, tags, keys, 0, body, true);
61 }
62
63 public void setKeys(String keys) {
64 this.putProperty(MessageConst.PROPERTY_KEYS, keys);
65 }
66
67 void putProperty(final String name, final String value) {
68 if (null == this.properties) {
69 this.properties = new HashMap<String, String>();
70 }
71
72 this.properties.put(name, value);
73 }
74
75 void clearProperty(final String name) {
76 if (null != this.properties) {
77 this.properties.remove(name);
78 }
79 }
80
81 public void putUserProperty(final String name, final String value) {
82 if (MessageConst.STRING_HASH_SET.contains(name)) {
83 throw new RuntimeException(String.format(
84 "The Property<%s> is used by system, input another please", name));
85 }
86
87 if (value == null || value.trim().isEmpty()
88 || name == null || name.trim().isEmpty()) {
89 throw new IllegalArgumentException(
90 "The name or value of property can not be null or blank string!"
91 );
92 }
93
94 this.putProperty(name, value);
95 }
96
97 public String getUserProperty(final String name) {
98 return this.getProperty(name);
99 }
100
101 public String getProperty(final String name) {
102 if (null == this.properties) {
103 this.properties = new HashMap<String, String>();
104 }
105
106 return this.properties.get(name);
107 }
108
109 public String getTopic() {
110 return topic;
111 }
112
113 public void setTopic(String topic) {
114 this.topic = topic;
115 }
116
117 public String getTags() {
118 return this.getProperty(MessageConst.PROPERTY_TAGS);
119 }
120
121 public void setTags(String tags) {
122 this.putProperty(MessageConst.PROPERTY_TAGS, tags);
123 }
124
125 public String getKeys() {
126 return this.getProperty(MessageConst.PROPERTY_KEYS);
127 }
128
129 public void setKeys(Collection<String> keys) {
130 StringBuffer sb = new StringBuffer();
131 for (String k : keys) {
132 sb.append(k);
133 sb.append(MessageConst.KEY_SEPARATOR);
134 }
135
136 this.setKeys(sb.toString().trim());
137 }
138
139 public int getDelayTimeLevel() {
140 String t = this.getProperty(MessageConst.PROPERTY_DELAY_TIME_LEVEL);
141 if (t != null) {
142 return Integer.parseInt(t);
143 }
144
145 return 0;
146 }
147
148 public void setDelayTimeLevel(int level) {
149 this.putProperty(MessageConst.PROPERTY_DELAY_TIME_LEVEL, String.valueOf(level));
150 }
151
152 public boolean isWaitStoreMsgOK() {
153 String result = this.getProperty(MessageConst.PROPERTY_WAIT_STORE_MSG_OK);
154 if (null == result)
155 return true;
156
157 return Boolean.parseBoolean(result);
158 }
159
160 public void setWaitStoreMsgOK(boolean waitStoreMsgOK) {
161 this.putProperty(MessageConst.PROPERTY_WAIT_STORE_MSG_OK, Boolean.toString(waitStoreMsgOK));
162 }
163
164 public void setInstanceId(String instanceId) {
165 this.putProperty(MessageConst.PROPERTY_INSTANCE_ID, instanceId);
166 }
167
168 public int getFlag() {
169 return flag;
170 }
171
172 public void setFlag(int flag) {
173 this.flag = flag;
174 }
175
176 public byte[] getBody() {
177 return body;
178 }
179
180 public void setBody(byte[] body) {
181 this.body = body;
182 }
183
184 public Map<String, String> getProperties() {
185 return properties;
186 }
187
188 void setProperties(Map<String, String> properties) {
189 this.properties = properties;
190 }
191
192 public String getBuyerId() {
193 return getProperty(MessageConst.PROPERTY_BUYER_ID);
194 }
195
196 public void setBuyerId(String buyerId) {
197 putProperty(MessageConst.PROPERTY_BUYER_ID, buyerId);
198 }
199
200 public String getTransactionId() {
201 return transactionId;
202 }
203
204 public void setTransactionId(String transactionId) {
205 this.transactionId = transactionId;
206 }
207
208 @Override
209 public String toString() {
210 return "Message{" +
211 "topic='" + topic + '\'' +
212 ", flag=" + flag +
213 ", properties=" + properties +
214 ", body=" + Arrays.toString(body) +
215 ", transactionId='" + transactionId + '\'' +
216 '}';
217 }
218 }
topic：主题名字，可以通过 RocketMQ Console 创建。
flag：目前没用。
properties：消息扩展信息，Tag、keys、延迟级别都保存在这里。
body：消息体，字节数组。需要主席生产者使用什么编码，消费者也必须使用相同的编码解码，否则会产生乱码。
setKeys()：设置消息的key，多个key可以用MessageConst.KEY_SEPARATOR (空格)分隔或者直接用另一个重载方法。如果Broker中messageIndexEnable=true则会根据key创建消息的Hash索引，帮助用户进行快速查询。
1 public void setKeys(Collection<String> keys) {
2 StringBuffer sb = new StringBuffer();
3 for (String k : keys) {
4 sb.append(k);
5 sb.append(MessageConst.KEY_SEPARATOR);
6 }
7
8 this.setKeys(sb.toString().trim());
9 }
settags()：消息过滤的标记，用户可以订阅某个Topic的某些tag，这样broker只会把订阅了topic-tag的消息发送给消费者。
setDelayTimeLevel()：设置延迟级别，延迟多久消费者可以消费。
putUserProperty()：如果还有其他扩展信息，可以存放在这里。内部是一个Map，重复调用会覆盖旧值。
RocketMQ支持普通消息、分区有序消息、全局有序消息、延迟消息和事务消息。
普通消息：没有特殊功能的消息。普通消息也称为并发消息，和传统的队列相比，并发消息没有顺序，但是生产消息都是并发进行的，单机性能可达到十万级别的TPS。
分区有序消息：与kafka中的分区类似，把一个Topic消息分为多个分区 "保存" 和消费，在一个分区内的消息就是传统的队列，遵循FIFO(先进先出)原则。
全局有序消息：如果把一个Topic的分区数设置为1，那么该Topic中的消息就是单分区，所有的消息都遵循FIFO(先进先出)的原则。
延迟消息：消息发送后，消费者要在一定时间后，或者指定某个时间点才可以消费。在没有延迟消息时，基本的做法是基于定时计划任务调度，定时发送消息。在RocketMQ中只需要在发送消息时设置延迟级别即可实现。
事务消息：主要涉及分布式事务，即需要保证在多个操作同时成功或者同时失败时，消费者才能消费消息。RocketMQ通过发送Half消息、处理本地事务、提交（Commit）消费或者回滚（Rollback）消息优雅地实现分布式事务。
三、生产者高可用
通常，我们希望不管Broker、Namesrv出现什么情况，发送消息都不要出现未知状态或者消息丢失。在消息发送的过程中，客户端、Broker、Namesrv都有可能发生服务器损坏、掉电等各种故障。当这些故障发生时，RocketMQ是怎么处理的呢？
1、客户端保证
第一种保证机制：重试机制。RocketMQ支持同步、异步发送，不管哪种方式都可以在配置失败后重试，如果单个Broker发生故障，重试会选择其他Broker保证消息正常发送。
配置项retryTimesWhenSendFailed: 同步发送失败重投次数，默认为2，因此生产者会最多尝试发送retryTimesWhenSendFailed + 1次。不会选择上次失败的broker，尝试向其他broker发送，最大程度保证消息不丢。超过重投次数，抛出异常，由客户端保证消息不丢。当出现RemotingException、MQClientException和部分MQBrokerException时会重投。
同步发送的重试代码可以参考，D:\rocketmq-master\client\src\main\java\org\apache\rocketmq\client\impl\producer\DefaultMQProducerImpl.java (rocketmq-all-4.8.0)
1 @org.jetbrains.annotations.Nullable 2 private SendResult sendDefaultImpl( 3 Message msg, 4 final CommunicationMode communicationMode, 5 final SendCallback sendCallback, 6 final long timeout 7 ) throws MQClientException, RemotingException, MQBrokerException, InterruptedException { 8 this.makeSureStateOK(); 9 Validators.checkMessage(msg, this.defaultMQProducer); 10 final long invokeID = random.nextLong(); 11 long beginTimestampFirst = System.currentTimeMillis(); 12 long beginTimestampPrev = beginTimestampFirst; 13 long endTimestamp = beginTimestampFirst; 14 TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic()); 15 if (topicPublishInfo != null && topicPublishInfo.ok()) { 16 boolean callTimeout = false; 17 MessageQueue mq = null; 18 Exception exception = null; 19 SendResult sendResult = null; 20 int timesTotal = communicationMode == CommunicationMode.SYNC ? 1 + this.defaultMQProducer.getRetryTimesWhenSendFailed() : 1; 21 int times = 0; 22 String[] brokersSent = new String[timesTotal]; 23 for (; times < timesTotal; times++) { 24 String lastBrokerName = null == mq ? null : mq.getBrokerName(); 25 MessageQueue mqSelected = this.selectOneMessageQueue(topicPublishInfo, lastBrokerName); 26 if (mqSelected != null) { 27 mq = mqSelected; 28 brokersSent[times] = mq.getBrokerName(); 29 try { 30 beginTimestampPrev = System.currentTimeMillis(); 31 if (times > 0) { 32 //Reset topic with namespace during resend. 33 msg.setTopic(this.defaultMQProducer.withNamespace(msg.getTopic())); 34 } 35 long costTime = beginTimestampPrev - beginTimestampFirst; 36 if (timeout < costTime) { 37 callTimeout = true; 38 break; 39 } 40 41 sendResult = this.sendKernelImpl(msg, mq, communicationMode, sendCallback, topicPublishInfo, timeout - costTime); 42 endTimestamp = System.currentTimeMillis(); 43 this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false); 44 switch (communicationMode) { 45 case ASYNC: 46 return null; 47 case ONEWAY: 48 return 49 ..........null; 50 case SYNC: 51 if (sendResult.getSendStatus() != SendStatus.SEND_OK) { 52 if (this.defaultMQProducer.isRetryAnotherBrokerWhenNotStoreOK()) { 53 continue; 54 } 55 } 56 57 return sendResult; 58 default: 59 break; 60 } 61 } catch (RemotingException e) { 62 endTimestamp = System.currentTimeMillis(); 63 this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, true); 64 log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e); 65 log.warn(msg.toString()); 66 exception = e; 67 continue; 68 } catch (MQClientException e) { 69 endTimestamp = System.currentTimeMillis(); 70 this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, true); 71 log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e); 72 log.warn(msg.toString()); 73 exception = e; 74 continue; 75 } catch (MQBrokerException e) { 76 endTimestamp = System.currentTimeMillis(); 77 this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, true); 78 log.warn(String.format("sendKernelImpl exception, resend at once, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e); 79 log.warn(msg.toString()); 80 exception = e; 81 switch (e.getResponseCode()) { 82 case ResponseCode.TOPIC_NOT_EXIST: 83 case ResponseCode.SERVICE_NOT_AVAILABLE: 84 case ResponseCode.SYSTEM_ERROR: 85 case ResponseCode.NO_PERMISSION: 86 case ResponseCode.NO_BUYER_ID: 87 case ResponseCode.NOT_IN_CURRENT_UNIT: 88 continue; 89 default: 90 if (sendResult != null) { 91 return sendResult; 92 } 93 94 throw e; 95 } 96 } catch (InterruptedException e) { 97 endTimestamp = System.currentTimeMillis(); 98 this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false); 99 log.warn(String.format("sendKernelImpl exception, throw exception, InvokeID: %s, RT: %sms, Broker: %s", invokeID, endTimestamp - beginTimestampPrev, mq), e); 100 log.warn(msg.toString()); 101 102 log.warn("sendKernelImpl exception", e); 103 log.warn(msg.toString()); 104 throw e; 105 } 106 } else { 107 break; 108 } 109 } 110 111 if (sendResult != null) { 112 return sendResult; 113 } 114 115 String info = String.format("Send [%d] times, still failed, cost [%d]ms, Topic: %s, BrokersSent: %s", 116 times, 117 System.currentTimeMillis() - beginTimestampFirst, 118 msg.getTopic(), 119 Arrays.toString(brokersSent)); 120 121 info += FAQUrl.suggestTodo(FAQUrl.SEND_MSG_FAILED); 122 123 MQClientException mqClientException = new MQClientException(info, exception); 124 if (callTimeout) { 125 throw new RemotingTooMuchRequestException("sendDefaultImpl call timeout"); 126 } 127 128 if (exception instanceof MQBrokerException) { 129 mqClientException.setResponseCode(((MQBrokerException) exception).getResponseCode()); 130 } else if (exception instanceof RemotingConnectException) { 131 mqClientException.setResponseCode(ClientErrorCode.CONNECT_BROKER_EXCEPTION); 132 } else if (exception instanceof RemotingTimeoutException) { 133 mqClientException.setResponseCode(ClientErrorCode.ACCESS_BROKER_TIMEOUT); 134 } else if (exception instanceof MQClientException) { 135 mqClientException.setResponseCode(ClientErrorCode.BROKER_NOT_EXIST_EXCEPTION); 136 } 137 138 throw mqClientException; 139 }
异步发送重试代码可以参考,D:\rocketmq-master\client\src\main\java\org\apache\rocketmq\client\impl\MQClientAPIImpl.java (rocketmq-all-4.8.0)
1 private void sendMessageAsync( 2 final String addr, 3 final String brokerName, 4 final Message msg, 5 final long timeoutMillis, 6 final RemotingCommand request, 7 final SendCallback sendCallback, 8 final TopicPublishInfo topicPublishInfo, 9 final MQClientInstance instance, 10 final int retryTimesWhenSendFailed, 11 final AtomicInteger times, 12 final SendMessageContext context, 13 final DefaultMQProducerImpl producer 14 ) throws InterruptedException, RemotingException { 15 final long beginStartTime = System.currentTimeMillis(); 16 this.remotingClient.invokeAsync(addr, request, timeoutMillis, new InvokeCallback() { 17 @Override 18 public void operationComplete(ResponseFuture responseFuture) { 19 long cost = System.currentTimeMillis() - beginStartTime; 20 RemotingCommand response = responseFuture.getResponseCommand(); 21 if (null == sendCallback && response != null) { 22 23 try { 24 SendResult sendResult = MQClientAPIImpl.this.processSendResponse(brokerName, msg, response, addr); 25 if (context != null && sendResult != null) { 26 context.setSendResult(sendResult); 27 context.getProducer().executeSendMessageHookAfter(context); 28 } 29 } catch (Throwable e) { 30 } 31 32 producer.updateFaultItem(brokerName, System.currentTimeMillis() - responseFuture.getBeginTimestamp(), false); 33 return; 34 } 35 36 if (response != null) { 37 try { 38 SendResult sendResult = MQClientAPIImpl.this.processSendResponse(brokerName, msg, response, addr); 39 assert sendResult != null; 40 if (context != null) { 41 context.setSendResult(sendResult); 42 context.getProducer().executeSendMessageHookAfter(context); 43 } 44 45 try { 46 sendCallback.onSuccess(sendResult); 47 } catch (Throwable e) { 48 } 49 50 producer.updateFaultItem(brokerName, System.currentTimeMillis() - responseFuture.getBeginTimestamp(), false); 51 } catch (Exception e) { 52 producer.updateFaultItem(brokerName, System.currentTimeMillis() - responseFuture.getBeginTimestamp(), true); 53 onExceptionImpl(brokerName, msg, timeoutMillis - cost, request, sendCallback, topicPublishInfo, instance, 54 retryTimesWhenSendFailed, times, e, context, false, producer); 55 } 56 } else { 57 producer.updateFaultItem(brokerName, System.currentTimeMillis() - responseFuture.getBeginTimestamp(), true); 58 if (!responseFuture.isSendRequestOK()) { 59 MQClientException ex = new MQClientException("send request failed", responseFuture.getCause()); 60 onExceptionImpl(brokerName, msg, timeoutMillis - cost, request, sendCallback, topicPublishInfo, instance, 61 retryTimesWhenSendFailed, times, ex, context, true, producer); 62 } else if (responseFuture.isTimeout()) { 63 MQClientException ex = new MQClientException("wait response timeout " + responseFuture.getTimeoutMillis() + "ms", 64 responseFuture.getCause()); 65 onExceptionImpl(brokerName, msg, timeoutMillis - cost, request, sendCallback, topicPublishInfo, instance, 66 retryTimesWhenSendFailed, times, ex, context, true, producer); 67 } else { 68 MQClientException ex = new MQClientException("unknow reseaon", responseFuture.getCause()); 69 onExceptionImpl(brokerName, msg, timeoutMillis - cost, request, sendCallback, topicPublishInfo, instance, 70 retryTimesWhenSendFailed, times, ex, context, true, producer); 71 } 72 } 73 } 74 }); 75 }
通信是在通信层异步发送发完成的，当operationComplete()方法返回的response值为null时，会重新执行重试代码。返回值response为null通常是因为客户端收到TCP请求解包失败，或者没有找到匹配的request。
生产者配置项RetryTimesWhenSendAsyncFailed表示异步重试的次数，异步重试不会选择其他broker，仅在同一个broker上做重试，不保证消息不丢，默认为2次，加上正常发送的1次，总共有3次发送机会。
第二种保证机制：客户端容错。RocketMQ Client会维护一个 "Broker-发送延迟" 关系，根据这个关系选择一个发送延迟级别较低的 Broker 来发送消息，这样能最大限度地利用 Broker 的能力，剔除已经宕机、不可用或者发送延迟级别较高的 Broker，尽量保证消息的正常发送。
这种机制主要体现在发送消息时如何选择Queue，源代码在 D:\rocketmq-master\client\src\main\java\org\apache\rocketmq\client\latency\MQFaultStrategy.java (rocketmq-all-4.8.0)
1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 18 package org.apache.rocketmq.client.latency; 19 20 import org.apache.rocketmq.client.impl.producer.TopicPublishInfo; 21 import org.apache.rocketmq.client.log.ClientLogger; 22 import org.apache.rocketmq.logging.InternalLogger; 23 import org.apache.rocketmq.common.message.MessageQueue; 24 25 public class MQFaultStrategy { 26 private final static InternalLogger log = ClientLogger.getLog(); 27 private final LatencyFaultTolerance<String> latencyFaultTolerance = new LatencyFaultToleranceImpl(); 28 29 private boolean sendLatencyFaultEnable = false; 30 31 private long[] latencyMax = {50L, 100L, 550L, 1000L, 2000L, 3000L, 15000L}; 32 private long[] notAvailableDuration = {0L, 0L, 30000L, 60000L, 120000L, 180000L, 600000L}; 33 34 public long[] getNotAvailableDuration() { 35 return notAvailableDuration; 36 } 37 38 public void setNotAvailableDuration(final long[] notAvailableDuration) { 39 this.notAvailableDuration = notAvailableDuration; 40 } 41 42 public long[] getLatencyMax() { 43 return latencyMax; 44 } 45 46 public void setLatencyMax(final long[] latencyMax) { 47 this.latencyMax = latencyMax; 48 } 49 50 public boolean isSendLatencyFaultEnable() { 51 return sendLatencyFaultEnable; 52 } 53 54 public void setSendLatencyFaultEnable(final boolean sendLatencyFaultEnable) { 55 this.sendLatencyFaultEnable = sendLatencyFaultEnable; 56 } 57 58 public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) { 59 if (this.sendLatencyFaultEnable) { 60 try { 61 /* 第1步，获取一个在延迟上可接受，并且和上次发送相同的Broker。 62 首先获取一个自增序号index，通过取模获取Queue的位置下标Pos。 63 如果Pos对应的Broker的延迟时间是可以接受的，并且是第一次发送，或者和上次发送的Broker相同，则将Queue返回。 64 */ 65 int index = tpInfo.getSendWhichQueue().getAndIncrement(); 66 for (int i = 0; i < tpInfo.getMessageQueueList().size(); i++) { 67 int pos = Math.abs(index++) % tpInfo.getMessageQueueList().size(); 68 if (pos < 0) 69 pos = 0; 70 MessageQueue mq = tpInfo.getMessageQueueList().get(pos); 71 if (latencyFaultTolerance.isAvailable(mq.getBrokerName())) 72 return mq; 73 } 74 // 第2步，如果第1步没有选择一个Broker，则选择一个延迟较低的Broker 75 final String notBestBroker = latencyFaultTolerance.pickOneAtLeast(); 76 int writeQueueNums = tpInfo.getQueueIdByBroker(notBestBroker); 77 if (writeQueueNums > 0) { 78 final MessageQueue mq = tpInfo.selectOneMessageQueue(); 79 if (notBestBroker != null) { 80 mq.setBrokerName(notBestBroker); 81 mq.setQueueId(tpInfo.getSendWhichQueue().getAndIncrement() % writeQueueNums); 82 } 83 return mq; 84 } else { 85 latencyFaultTolerance.remove(notBestBroker); 86 } 87 } catch (Exception e) { 88 log.error("Error occurred when selecting message queue", e); 89 } 90 // 第3步，如果第1、第2步都没有选中一个Broker，则随机选择一个Broker。 91 return tpInfo.selectOneMessageQueue(); 92 } 93 94 return tpInfo.selectOneMessageQueue(lastBrokerName); 95 } 96 97 public void updateFaultItem(final String brokerName, final long currentLatency, boolean isolation) { 98 if (this.sendLatencyFaultEnable) { 99 long duration = computeNotAvailableDuration(isolation ? 30000 : currentLatency); 100 this.latencyFaultTolerance.updateFaultItem(brokerName, currentLatency, duration); 101 } 102 } 103 104 private long computeNotAvailableDuration(final long currentLatency) { 105 for (int i = latencyMax.length - 1; i >= 0; i--) { 106 if (currentLatency >= latencyMax[i]) 107 return this.notAvailableDuration[i]; 108 } 109 110 return 0; 111 } 112 }
sendLatencyFaultEnable： 发送延迟容错开关，默认为关闭，如果开关打开了，会触发发送延迟容错机制来选择发送Queue。
上面代码里包括一个随机选择方法tpInfo.selectOneMessageQueue(lastBrokerName)，该方法的功能就是随机一个Broker，具体实现如下：
D:\rocketmq-master\client\src\main\java\org\apache\rocketmq\client\impl\producer\TopicPublishInfo.java (rocketmq-all-4.8.0)
1 public MessageQueue selectOneMessageQueue(final String lastBrokerName) { 2 // 第1步，如果没有上次使用Broker作为参考，那么随机选择一个Broker 3 if (lastBrokerName == null) { 4 return selectOneMessageQueue(); 5 } else { 6 // 第2步，如果存在上次使用的Broker，就选择上次使用的Broker，目的是均匀分散Broker的压力。 7 for (int i = 0; i < this.messageQueueList.size(); i++) { 8 int index = this.sendWhichQueue.getAndIncrement(); 9 int pos = Math.abs(index) % this.messageQueueList.size(); 10 if (pos < 0) 11 pos = 0; 12 MessageQueue mq = this.messageQueueList.get(pos); 13 if (!mq.getBrokerName().equals(lastBrokerName)) { 14 return mq; 15 } 16 } 17 // 第3步，如果第1、第2步都没有选中一个Broker，则采用兜底方案——随机选择一个Broker 18 return selectOneMessageQueue(); 19 } 20 }
客户端在发送消息后，会调用 updateFaultItem()方法来更新当前接受消息的Broker的延迟情况，这些主要逻辑都在 MQFaultStrategy类中实现，延迟策略有一个标准接口 LatencyFaultTolerance。
2、Broker端保证
Broker 数据同步方式保证：
- 同步复制：指消息发送到Master Broker后，同步到Slave Broker才算发送成功；
- 异步复制：指消息发送到Master Broker后，即为发送成功。
在生产环境中，建议至少部署2个Master和2个Slave。
| 部署方式 | 优点 | 缺点 | 备注 |
| 单个Master模式 | 简单 |
这种方式风险较大，一旦Broker重启或者宕机时，会导致整个服务不可用
|
不建议线上环境使用，可用于本地测试 |
| 多个Master模式 | 配置简单，单个Master宕机或重启维护对应用无影响，在磁盘配置为RAID10时，即使机器宕机不可恢复情况下，由于RAID10磁盘非常可靠，消息也不会丢（异步刷盘丢失少量消息，同步刷盘一条不丢），性能最高。 | 单台机器宕机期间，这台机器上未被消费的消息在机器恢复之前不可订阅，消息实时性会收到影响。 | 当使用多master无slave的集群搭建方式时，master的brokerRole配置必须为ASYNC_MASTER。如果配置为SYNC_MASTER，则producer发送消息时，返回值的SendStatus会一直是SLAVE_NOT_AVAILABLE。 |
| 多Master多Slave模式——异步复制 | 即使磁盘损坏，消息丢失的非常少，但消息实时性不会受影响，因为Master宕机后，消费者仍然可以从Slave消费，此过程对应用透明，不需要人工干预，性能同多Master模式几乎一样。 | Master宕机，磁盘损坏情况，会丢失少量信息。 | |
| 多Master多Slave模式——同步双写 | 数据与服务都无单点，Master宕机情况下，消息无延迟，服务可用性与数据可用性都非常高； | 性能比异步复制模式稍低，大约低10%左右，发送单个消息的RT会稍高，目前主宕机后，备机不能自动切换为主机，后续会支持自动切换功能。 |
