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https://issues.apache.org/jira/browse/HDFS-14576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16886681#comment-16886681
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He Xiaoqiao commented on HDFS-14576:
------------------------------------

Thanks [~zhangchen] for your detailed comment, As you said above, BlockReport 
Lease is a good solution, and it could reduce load of NameNode. I believe there 
are still some points need to optimize on some scenarios, especially for 
NameNode restart stage.

> Avoid block report retry and slow down namenode startup
> -------------------------------------------------------
>
>                 Key: HDFS-14576
>                 URL: https://issues.apache.org/jira/browse/HDFS-14576
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: He Xiaoqiao
>            Assignee: He Xiaoqiao
>            Priority: Major
>
> During namenode startup, the load will be very high since it has to process 
> every datanodes blockreport one by one. If there are hundreds datanodes block 
> reports pending process, the issue will be more serious even 
> #processFirstBlockReport is processed a lot more efficiently than ordinary 
> block reports. Then some of datanode will retry blockreport and lengthens 
> restart times. I think we should filter the block report request (via 
> datanode blockreport retries) which has be processed and return directly then 
> shorten down restart time. I want to state this proposal may be obvious only 
> for large cluster.



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