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From "Dmytro Molkov (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1348) Improve NameNode reponsiveness while it is checking if datanode decommissions are complete
Date Wed, 01 Sep 2010 02:34:53 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1348?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12904882#action_12904882
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Dmytro Molkov commented on HDFS-1348:
-------------------------------------

I like the patch overall. Got two questions though: why did you choose 2000 blocks to check
at a time and do you think it might be worth to make it configurable? And the other one is
how much memory pressure would the checkedBlocks hash set add?

> 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: name-node
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>             Fix For: 0.22.0
>
>         Attachments: decommission.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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