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https://issues.apache.org/jira/browse/HDFS-16613?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17550940#comment-17550940
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Hiroyuki Adachi commented on HDFS-16613:
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[~caozhiqiang] , thank you for your explanation. It looks good.
Now I understand that the blocksToProcess controls the number of replication
works, so if it is less than dfs.namenode.replication.max-streams-hard-limit,
all blocks use replication on decommissioning node but not reconstruction.
Could you please tell me the value of
dfs.namenode.replication.max-streams-hard-limit and
dfs.namenode.replication.work.multiplier.per.iteration?
{code:java}
// BlockManager#computeDatanodeWork
final int blocksToProcess = numlive
* this.blocksReplWorkMultiplier;
final int nodesToProcess = (int) Math.ceil(numlive
* this.blocksInvalidateWorkPct);
int workFound = this.computeBlockReconstructionWork(blocksToProcess); {code}
> EC: Improve performance of decommissioning dn with many ec blocks
> -----------------------------------------------------------------
>
> Key: HDFS-16613
> URL: https://issues.apache.org/jira/browse/HDFS-16613
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: ec, erasure-coding, namenode
> Affects Versions: 3.4.0
> Reporter: caozhiqiang
> Assignee: caozhiqiang
> Priority: Major
> Labels: pull-request-available
> Attachments: image-2022-06-07-11-46-42-389.png,
> image-2022-06-07-17-42-16-075.png, image-2022-06-07-17-45-45-316.png,
> image-2022-06-07-17-51-04-876.png, image-2022-06-07-17-55-40-203.png
>
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> In a hdfs cluster with a lot of EC blocks, decommission a dn is very slow.
> The reason is unlike replication blocks can be replicated from any dn which
> has the same block replication, the ec block have to be replicated from the
> decommissioning dn.
> The configurations dfs.namenode.replication.max-streams and
> dfs.namenode.replication.max-streams-hard-limit will limit the replication
> speed, but increase these configurations will create risk to the whole
> cluster's network. So it should add a new configuration to limit the
> decommissioning dn, distinguished from the cluster wide max-streams limit.
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