欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页

ActiveMQ的消息重发策略和DLQ处理

程序员文章站 2022-06-12 14:22:06
...
在以下三种情况中,ActiveMQ消息会被重发给客户端/消费者:
1.使用一个事务session,并且调用了rollback()方法;
2.一个事务session,关闭之前调用了commit;
3.在session中使用CLIENT_ACKNOWLEDGE签收模式,并且调用了Session.recover()方法。

Broker根据自己的规则,通过BrokerInfo命令包和客户端建立连接,向客户端传送缺省发送策略。但是客户端可以使用ActiveMQConnection.getRedeliveryPolicy()方法覆盖override这个策略设置。
RedeliveryPolicy policy = connection.getRedeliveryPolicy();
policy.setInitialRedeliveryDelay(500);
policy.setBackOffMultiplier(2);
policy.setUseExponentialBackOff(true);
policy.setMaximumRedeliveries(2);

一旦消息重发尝试超过重发策略中配置的maximumRedeliveries(缺省为6次)时,会给broker发送一个"Poison ack",通知它,这个消息被认为是一个毒丸(a poison pill),接着broker会将这个消息发送到DLQ(Dead Letter Queue),以便后续分析处理。

缺省死信队列(Dead Letter Queue)叫做ActiveMQ.DLQ;所有的未送达消息都会被发送到这个队列,以致会非常难于管理。你可以设置activemq.xml文件中的destination policy map的"individualDeadLetterStrategy"属性来修改.
<broker...>
  <destinationPolicy>
    <policyMap>
      <policyEntries>
        <!-- Set the following policy on all queues using the '>' wildcard -->
        <policyEntry queue=">">
          <deadLetterStrategy>
            <!--
              Use the prefix 'DLQ.' for the destination name, and make
              the DLQ a queue rather than a topic
            -->
            <individualDeadLetterStrategy
              queuePrefix="DLQ." useQueueForQueueMessages="true" />
          </deadLetterStrategy>
        </policyEntry>
      </policyEntries>
    </policyMap>
  </destinationPolicy>
  ...
</broker>


自动丢弃过期消息(Expired Messages)
一些应用可能只是简单的丢弃过期消息,而不想将它们放到DLQ中,完全跳过了DLQ。在dead letter strategy死信策略上配置processExpired属性为false,可以实现这个功能。
<broker...>
  <destinationPolicy>
   <policyMap>
     <policyEntries>
       <!-- Set the following policy on all queues using the '>' wildcard -->
       <policyEntry queue=">">
         <!--
           Tell the dead letter strategy not to process expired messages
           so that they will just be discarded instead of being sent to
           the DLQ
         -->
         <deadLetterStrategy>
           <sharedDeadLetterStrategy processExpired="false" />
         </deadLetterStrategy>
       </policyEntry>
     </policyEntries>
   </policyMap>
  </destinationPolicy>
...
</broker>


将非持久消息(non-persistent messages)放入死信队列
ActiveMQ缺省不会将未发到的非持久消息放入死信队列。如果一个应用程序并不想将消息message设置为持久的,那么记录下来那些未发送到的消息对它来说往往也是没有价值的。不过如果想实现这个功能,可以在dead-letter strategy死信策略上设置processNonPersistent="true"
<broker...>
  <destinationPolicy>
   <policyMap>
     <policyEntries>
       <!-- Set the following policy on all queues using the '>' wildcard -->
       <policyEntry queue=">">
         <!--
           Tell the dead letter strategy to also place non-persisted messages
           onto the dead-letter queue if they can't be delivered.
         -->
         <deadLetterStrategy>
           <sharedDeadLetterStrategy processNonPersistent="true" />
         </deadLetterStrategy>
       </policyEntry>
     </policyEntries>
   </policyMap>
  </destinationPolicy>
...
</broker>