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https://issues.apache.org/jira/browse/HDDS-3481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17130067#comment-17130067
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Xiaoyu Yao commented on HDDS-3481:
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bq. The reason is source datanode replicates too many containers to other
datanode, so the source datanode become very slow.
Should we consider balancing the replication source among datanodes or throttle
the replication per datanode?
> SCM ask too many datanodes to replicate the same container
> ----------------------------------------------------------
>
> Key: HDDS-3481
> URL: https://issues.apache.org/jira/browse/HDDS-3481
> Project: Hadoop Distributed Data Store
> Issue Type: Bug
> Components: SCM
> Reporter: runzhiwang
> Assignee: runzhiwang
> Priority: Blocker
> Labels: TriagePending, pull-request-available
> Attachments: screenshot-1.png, screenshot-2.png, screenshot-3.png,
> screenshot-4.png
>
>
> *What's the problem ?*
> As the image shows, scm ask 31 datanodes to replicate container 2037 every
> 10 minutes from 2020-04-17 23:38:51. And at 2020-04-18 08:58:52 scm find the
> replicate num of container 2037 is 12, then it ask 11 datanodes to delete
> container 2037.
> !screenshot-1.png!
> !screenshot-2.png!
> *What's the reason ?*
> scm check whether (container replicates num +
> inflightReplication.get(containerId).size() -
> inflightDeletion.get(containerId).size()) is less than 3. If less than 3, it
> will ask some datanode to replicate the container, and add the action into
> inflightReplication.get(containerId). The replicate action time out is 10
> minutes, if action timeout, scm will delete the action from
> inflightReplication.get(containerId) as the image shows. Then (container
> replicates num + inflightReplication.get(containerId).size() -
> inflightDeletion.get(containerId).size()) is less than 3 again, and scm ask
> another datanode to replicate the container.
> Because replicate container cost a long time, sometimes it cannot finish in
> 10 minutes, thus 31 datanodes has to replicate the container every 10
> minutes. 19 of 31 datanodes replicate container from the same source
> datanode, it will also cause big pressure on the source datanode and
> replicate container become slower. Actually it cost 4 hours to finish the
> first replicate.
> !screenshot-4.png!
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