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https://issues.apache.org/jira/browse/HDFS-9434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15025422#comment-15025422
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Jason Lowe commented on HDFS-9434:
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This broke the 2.6 build. The patch is assuming SLF4J but that hasn't happened
on the 2.6 branch.
> Recommission a datanode with 500k blocks may pause NN for 30 seconds
> --------------------------------------------------------------------
>
> Key: HDFS-9434
> URL: https://issues.apache.org/jira/browse/HDFS-9434
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Tsz Wo Nicholas Sze
> Fix For: 2.6.3
>
> Attachments: h9434_20151116.patch
>
>
> In BlockManager, processOverReplicatedBlocksOnReCommission is called within
> the namespace lock. There is a (not very useful) log message printed in
> processOverReplicatedBlock. When there is a large number of blocks stored in
> a storage, printing the log message for each block can pause NN to process
> any other operations. We did see that it could pause NN for 30 seconds for
> a storage with 500k blocks.
> I suggest to change the log message to trace level as a quick fix.
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