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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:
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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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