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https://issues.apache.org/jira/browse/ROCKETMQ-184?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16017072#comment-16017072
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ASF GitHub Bot commented on ROCKETMQ-184:
-----------------------------------------

Github user lizhanhui commented on the issue:

    https://github.com/apache/incubator-rocketmq/pull/95
  
    +1


> It takes too long(3-33 seconds) to switch to read from slave when master 
> crashes
> --------------------------------------------------------------------------------
>
>                 Key: ROCKETMQ-184
>                 URL: https://issues.apache.org/jira/browse/ROCKETMQ-184
>             Project: Apache RocketMQ
>          Issue Type: Improvement
>          Components: rocketmq-client, rocketmq-remoting
>            Reporter: Jaskey Lam
>            Assignee: Xiaorui Wang
>             Fix For: 4.2.0-incubating
>
>
> When master crashes, no notifier callback is triggered to pull message again.
> Instead, it relies on the scan service to trigger timeout and then re pull.
> But the pulling command has 30 seconds timeout, and after timeout, pulling 
> operation will be scheduled after 3 seconds.
> So it takes 3 to 33 seconds to switch to slave, which is too long and can be 
> optimized.
> The root cause is the below repull cost too long to be triggered when master 
> crashes
> {code}
>             @Override
>             public void onException(Throwable e) {
>                 if 
> (!pullRequest.getMessageQueue().getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX))
>  {
>                     log.warn("execute the pull request exception", e);
>                 }
>                 
> DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest, 
> PULL_TIME_DELAY_MILLS_WHEN_EXCEPTION);
>             }
> {code}



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