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https://issues.apache.org/jira/browse/HDFS-16070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17363358#comment-17363358
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zhengchenyu commented on HDFS-16070:
------------------------------------

[~ayushsaxena][~inigoiri] I have submit a pull request, can you help me review 
this patch?

> DataTransfer block storm when datanode's io is busy.
> ----------------------------------------------------
>
>                 Key: HDFS-16070
>                 URL: https://issues.apache.org/jira/browse/HDFS-16070
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 3.3.0, 3.2.1
>            Reporter: zhengchenyu
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> When I speed up the decommission, I found that some datanode's io is busy, 
> then I found host's load is very high, and ten thousands data transfer thread 
> are running. 
> Then I find log like below.
> {code}
> # 启动线程的日志
> 2021-06-08 13:42:37,620 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: 
> DatanodeRegistration(10.201.4.49:9866, 
> datanodeUuid=6c55b7cb-f8ef-445b-9cca-d82b5b077ed1, infoPort=9864, 
> infoSecurePort=0, ipcPort=9867, 
> storageInfo=lv=-57;cid=CID-37e80bd5-733a-4d7b-ba3d-b46269573c72;nsid=215490653;c=1584525570797)
>  Starting thread to transfer 
> BP-852924019-10.201.1.32-1584525570797:blk_-9223372036449848858_30963611 to 
> 10.201.7.52:9866
> 2021-06-08 13:52:36,345 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: 
> DatanodeRegistration(10.201.4.49:9866, 
> datanodeUuid=6c55b7cb-f8ef-445b-9cca-d82b5b077ed1, infoPort=9864, 
> infoSecurePort=0, ipcPort=9867, 
> storageInfo=lv=-57;cid=CID-37e80bd5-733a-4d7b-ba3d-b46269573c72;nsid=215490653;c=1584525570797)
>  Starting thread to transfer 
> BP-852924019-10.201.1.32-1584525570797:blk_-9223372036449848858_30963611 to 
> 10.201.7.31:9866
> 2021-06-08 14:02:37,197 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: 
> DatanodeRegistration(10.201.4.49:9866, 
> datanodeUuid=6c55b7cb-f8ef-445b-9cca-d82b5b077ed1, infoPort=9864, 
> infoSecurePort=0, ipcPort=9867, 
> storageInfo=lv=-57;cid=CID-37e80bd5-733a-4d7b-ba3d-b46269573c72;nsid=215490653;c=1584525570797)
>  Starting thread to transfer 
> BP-852924019-10.201.1.32-1584525570797:blk_-9223372036449848858_30963611 to 
> 10.201.16.50:9866
> # 发送完成的标记
> 2021-06-08 13:54:08,134 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: 
> DataTransfer, at bd-tz1-hadoop-004049.zeus.lianjia.com:9866: Transmitted 
> BP-852924019-10.201.1.32-1584525570797:blk_-9223372036449848858_30963611 
> (numBytes=7457424) to /10.201.7.52:9866
> 2021-06-08 14:10:47,170 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: 
> DataTransfer, at bd-tz1-hadoop-004049.zeus.lianjia.com:9866: Transmitted 
> BP-852924019-10.201.1.32-1584525570797:blk_-9223372036449848858_30963611 
> (numBytes=7457424) to /10.201.16.50:9866
> {code}
> You will see last datatranfser thread was done on 13:54:08, but next 
> datatranfser was start at 13:52:36. 
> If datatranfser was not done in 10min(pending timeout + check interval), then 
> next datatranfser for same block will be running. Then disk and network are 
> heavy.



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