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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1348) Improve NameNode reponsiveness while it is checking if datanode decommissions are complete
Date Mon, 02 Mar 2015 22:40:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14343920#comment-14343920
] 

Konstantin Shvachko commented on HDFS-1348:
-------------------------------------------

This is still a valid optimization. The code moved with write and read locks, but the granularity
of locking for decommissioning checks is still 5 DNs at a time. And the nodes got bigger drives
than 5 years ago.
Too bad we did not commit it back then.

> Improve NameNode reponsiveness while it is checking if datanode decommissions are complete
> ------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1348
>                 URL: https://issues.apache.org/jira/browse/HDFS-1348
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>         Attachments: decomissionImp1.patch, decomissionImp2.patch, decommission.patch,
decommission1.patch
>
>
> NameNode normally is busy all the time. Its log is full of activities every second. But
once for a while, NameNode seems to pause for more than 10 seconds without doing anything,
leaving a blank in its log even though no garbage collection is happening.  All other requests
to NameNode are blocked when this is happening.
> One culprit is DecommionManager. Its monitor holds the fsynamesystem lock during the
whole process of checking if decomissioning DataNodes are finished or not, during which it
checks every block of up to a default of 5 datanodes.



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