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Posted to dev@rocketmq.apache.org by GitBox <gi...@apache.org> on 2022/07/31 11:08:22 UTC

[GitHub] [rocketmq] mz0113 opened a new issue, #4742: 消费者consumer调用 resetOffset 时pullRequest没清理导致可能存在的一个概率性BUG

mz0113 opened a new issue, #4742:
URL: https://github.com/apache/rocketmq/issues/4742

   
   
   版本：v4.9.3和v4.9.4 都存在
   代码位置：org.apache.rocketmq.client.impl.factory.MQClientInstance#resetOffset
   
   ![image](https://user-images.githubusercontent.com/42512469/182022748-ae056af9-5555-401a-947d-b0a75ac7e80a.png)
   
   我调用上述API希望重置消费端位移,但是我感觉有2个概率性BUG
   第一个：
   consumer.updateConsumeOffset(mq, offset); 
   这一句执行完毕后,会把提交位移重置为我传入的位移参数,但是问题就出现了,如果当时消费线程A已经走到了updateConsumeOffset()这段代码，在刚才设置processQueue.drpped(true)时候就已经过了那个下图220行的卡控了,那么消费线程A就会提交位移把我自己传入的位移覆盖掉！
   ![image](https://user-images.githubusercontent.com/42512469/182023058-1c1a9fac-01a3-47c9-af1e-ddd05c1b6c28.png)
   所以我认为在消费线程设置完位移之后应该在此判断是否dropped了,如果为true,应该撤销位移的提交,当然这个也不是完全准确。理论上要加锁处理
   
   
   第二个：
   还是第一张图上,虽然调用了 iterator.remove(); 把processQueue移除掉了,但是此时可能还有pullRequest正在拉取消息（同样的也是先拉取消息的路上了，才设置suspend标记或者dropped processQueue，此时因为卡控已经代码走过去了，所以卡控无效）。然后消息拉取回来以后在callBack中又会继续拉取消息，但其实这个pullRequest不应该反复再去拉消息了，因为它拉消息用的nextBeginOffset是重置offset之前的那个。
   ![image](https://user-images.githubusercontent.com/42512469/182023258-bccbf4eb-3f46-49ae-b96d-e7991b9e9928.png)
   
   


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[GitHub] [rocketmq] duhenglucky closed issue #4742: 消费者consumer调用 resetOffset 时pullRequest没清理导致可能存在的一个概率性BUG

Posted by GitBox <gi...@apache.org>.

duhenglucky closed issue #4742: 消费者consumer调用 resetOffset 时pullRequest没清理导致可能存在的一个概率性BUG
URL: https://github.com/apache/rocketmq/issues/4742


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[GitHub] [rocketmq] duhenglucky commented on issue #4742: 消费者consumer调用 resetOffset 时pullRequest没清理导致可能存在的一个概率性BUG

Posted by GitBox <gi...@apache.org>.

duhenglucky commented on issue #4742:
URL: https://github.com/apache/rocketmq/issues/4742#issuecomment-1204829221

   @mz0113 对代码的分析非常的细致，上面的问题确实存在，考虑到重置位点这个运维动作，并不是非常经常性的动作，但是位点的提交却是一个比较经常发生的行为，所以这里没有加一些更为复杂的逻辑去严格控制位点重置的有效性，可以通过多次重置来进行补偿，当然这个逻辑确实值得优化，比如将需要重置的位点放到服务端，替换掉客户端请求的位点，有兴趣的话，欢迎提交PR做一些尝试来进行优化。


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