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https://issues.apache.org/jira/browse/HDFS-17267?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17791557#comment-17791557
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farmmamba commented on HDFS-17267:
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[~hexiaoqiao]  [~zhangshuyan] [~tomscut] [~ayushsaxena]  IIRC, I think we can 
optimize this case.  Sir, please correct me if i was wrong.  Hope to receive 
your replys~ Thanks a lot.

> Client send the smae packet multiple times when method markSlowNode throws 
> IOException.
> ---------------------------------------------------------------------------------------
>
>                 Key: HDFS-17267
>                 URL: https://issues.apache.org/jira/browse/HDFS-17267
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 3.3.6
>            Reporter: farmmamba
>            Assignee: farmmamba
>            Priority: Major
>
> Since we have HDFS-16348, we can kick out SLOW node in pipeline when writing 
> data to pipeline. 
> And I think it introduced a problem, that is the same packet will be sent 
> twice or more times when we kick out SLOW node.
>  
> The flow are as below:
> 1、 DFSPacket p1 is pushed into dataQueue.
> 2、DataStreamer takes DFSPacket p1 from dataQueue.
> 3、Remove p1 from dataQueue and   push p1 into ackQueue.
> 4、sendPacket(p1).
> 5、In ResponseProcessor#run,  read pipelineAck for p1.
> 6、We meet SlOW node,  so method markSlowNode throw IOException and does not 
> execute `ackQueue.removeFirst();`.
> 7、In next loop of DataStreamer#run, we come into method 
> processDatanodeOrExternalError and execute `dataQueue.addAll(0, ackQueue);`.
> 8、the p1 will be sent repeatedly.
>  



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