NameServer为了简化和客户端通信，发现Broker故障时并不会立即通知客户端。故障规避机制就是用来解决当Broker出现故障，Producer不能及时感知而导致消息发送失败的问题。默认不开启，如果开启，消息发送失败的时候会将失败的Broker暂时排除在队列选择列表外
MQFaultStrategy类的：
public class MQFaultStrategy {
private final static InternalLogger log = ClientLogger.getLog();
private final LatencyFaultTolerance<String> latencyFaultTolerance = new LatencyFaultToleranceImpl();
private boolean sendLatencyFaultEnable = false;
private long[] latencyMax = {50L, 100L, 550L, 1000L, 2000L, 3000L, 15000L};
private long[] notAvailableDuration = {0L, 0L, 30000L, 60000L, 120000L, 180000L, 600000L};
public long[] getNotAvailableDuration() {
return notAvailableDuration;
}
public void setNotAvailableDuration(final long[] notAvailableDuration) {
this.notAvailableDuration = notAvailableDuration;
}
public long[] getLatencyMax() {
return latencyMax;
}
public void setLatencyMax(final long[] latencyMax) {
this.latencyMax = latencyMax;
}
public boolean isSendLatencyFaultEnable() {
return sendLatencyFaultEnable;
}
public void setSendLatencyFaultEnable(final boolean sendLatencyFaultEnable) {
this.sendLatencyFaultEnable = sendLatencyFaultEnable;
}
public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {
//是否开启故障延迟机制
if (this.sendLatencyFaultEnable) {
try {
int index = tpInfo.getSendWhichQueue().getAndIncrement();
for (int i = 0; i < tpInfo.getMessageQueueList().size(); i++) {
int pos = Math.abs(index++) % tpInfo.getMessageQueueList().size();
if (pos < 0)
pos = 0;
MessageQueue mq = tpInfo.getMessageQueueList().get(pos);
//判断Queue是否可用
if (latencyFaultTolerance.isAvailable(mq.getBrokerName())) {
if (null == lastBrokerName || mq.getBrokerName().equals(lastBrokerName))
return mq;
}
}
final String notBestBroker = latencyFaultTolerance.pickOneAtLeast();
int writeQueueNums = tpInfo.getQueueIdByBroker(notBestBroker);
if (writeQueueNums > 0) {
final MessageQueue mq = tpInfo.selectOneMessageQueue();
if (notBestBroker != null) {
mq.setBrokerName(notBestBroker);
mq.setQueueId(tpInfo.getSendWhichQueue().getAndIncrement() % writeQueueNums);
}
return mq;
} else {
latencyFaultTolerance.remove(notBestBroker);
}
} catch (Exception e) {
log.error("Error occurred when selecting message queue", e);
}
return tpInfo.selectOneMessageQueue();
}
//默认轮询
return tpInfo.selectOneMessageQueue(lastBrokerName);
}
public void updateFaultItem(final String brokerName, final long currentLatency, boolean isolation) {
if (this.sendLatencyFaultEnable) {
long duration = computeNotAvailableDuration(isolation ? 30000 : currentLatency);
this.latencyFaultTolerance.updateFaultItem(brokerName, currentLatency, duration);
}
}
private long computeNotAvailableDuration(final long currentLatency) {
for (int i = latencyMax.length - 1; i >= 0; i--) {
if (currentLatency >= latencyMax[i])
return this.notAvailableDuration[i];
}
return 0;
}
}在选择查找路由时，选择消息队列的关键步骤：
- 先按轮询算法选择一个消息队列
- 从故障列表判断该消息队列是否可用
LatencyFaultToleranceImpl中判断是否可用：
@Override
public boolean isAvailable(final String name) {
final FaultItem faultItem = this.faultItemTable.get(name);
if (faultItem != null) {
return faultItem.isAvailable();
}
return true;
}
public boolean isAvailable() {
return (System.currentTimeMillis() - startTimestamp) >= 0;
}- 判断是否在故障列表中，不在故障列表中代表可用。
- 在故障列表中判断当前时间是否大于等于故障规避的开始时间
startTimestamp
在消息发送结束后和发送出现异常时调用updateFaultItem()方法来更新故障列表，computeNotAvailableDuration()根据响应时间来计算故障周期时长，响应时间越长故障周期越长。网络异常、Broker异常、客户端异常都是固定响应时长30s，它们故障周期时长为10分钟。消息发送成功或线程中断异常响应时间在100毫秒以内，故障周期时长为0。
LatencyFaultToleranceImpl类的updateFaultItem方法：
@Override
public void updateFaultItem(final String name, final long currentLatency, final long notAvailableDuration) {
FaultItem old = this.faultItemTable.get(name);
if (null == old) {
final FaultItem faultItem = new FaultItem(name);
faultItem.setCurrentLatency(currentLatency);
faultItem.setStartTimestamp(System.currentTimeMillis() + notAvailableDuration);
//加入故障列表
old = this.faultItemTable.putIfAbsent(name, faultItem);
if (old != null) {
old.setCurrentLatency(currentLatency);
old.setStartTimestamp(System.currentTimeMillis() + notAvailableDuration);
}
} else {
old.setCurrentLatency(currentLatency);
old.setStartTimestamp(System.currentTimeMillis() + notAvailableDuration);
}
}FaultItem存储Broker名称、响应时长、故障规避开始时间，最重要的是故障规避开始时间，用来判断Queue是否可用
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