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https://issues.apache.org/jira/browse/HDFS-9434?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15015049#comment-15015049
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Hudson commented on HDFS-9434:
------------------------------

FAILURE: Integrated in Hadoop-Hdfs-trunk-Java8 #622 (See 
[https://builds.apache.org/job/Hadoop-Hdfs-trunk-Java8/622/])
HDFS-9434. Recommission a datanode with 500k blocks may pause NN for 30 
(szetszwo: rev 8e03e855b6a0cf650f43aac47b1ec642caf493f5)
* 
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockManager.java
* hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt


> 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: 2.7.2
>
>         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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