RocketMQ源码分析----Producer队列选择与容错策略

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队列选择

在HA的文章里大概讲了一下Producer如何为高可用贡献出一份力量的，当时只是说了遍历列表选择队列，然后选择一个，没有深入分析，这篇文章深入分析一下其源码，首先从发送消息选择队列的代码开始：

    String lastBrokerName = null == mq ? null : mq.getBrokerName();MessageQueue tmpmq = this.selectOneMessageQueue(lastBrokerName);
if (tmpmq != null) {mq = tmpmq;
//....

如上，如果发送失败了，重试的时候lastBrokerName将不为空，进入到selectOneMessageQueue方法

    public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {return this.mqFaultStrategy.selectOneMessageQueue(tpInfo, lastBrokerName);}

具体实现在mqFaultStrategy中

    public MessageQueue selectOneMessageQueue(final TopicPublishInfo tpInfo, final String lastBrokerName) {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);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);