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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12137) DN dataset lock should be fair
Date Fri, 14 Jul 2017 20:40:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12137?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16088022#comment-16088022
] 

Kihwal Lee commented on HDFS-12137:
-----------------------------------

+1 the patch looks good.  The test failure is not related.

> DN dataset lock should be fair
> ------------------------------
>
>                 Key: HDFS-12137
>                 URL: https://issues.apache.org/jira/browse/HDFS-12137
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>    Affects Versions: 2.8.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>            Priority: Critical
>         Attachments: HDFS-12137.branch-2.patch, HDFS-12137.trunk.patch, HDFS-12137.trunk.patch
>
>
> The dataset lock is very highly contended.  The unfair nature can be especially harmful
to the heartbeat handling.  Under high loads, partially expose by HDFS-12136 introducing disk
i/o within the lock, the heartbeat handling thread may process commands so slowly due to the
contention that the node becomes stale or falsely declared dead.  The unfair lock is not helping
and appears to be causing frequent starvation under load.



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