[jira] [Resolved] (HDFS-9434) Recommission a datanode with 500k blocks may pause NN for 30 seconds

["Tsz Wo Nicholas Sze (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-9434?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tsz Wo Nicholas Sze resolved HDFS-9434.
---------------------------------------
    Resolution: Fixed

Sangjin, thanks for the review.

I have committed the branch-2.6 patch.

> 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, h9434_20151116_branch-2.6.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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