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https://issues.apache.org/jira/browse/HDFS-8896?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jing Zhao updated HDFS-8896:
----------------------------
       Resolution: Fixed
     Hadoop Flags: Reviewed
    Fix Version/s: 2.8.0
           Status: Resolved  (was: Patch Available)

The patch looks good to me. +1. I've committed this to trunk and branch-2. 
Thanks Walter!

> DataNode object isn't GCed when shutdown, because it has GC root in 
> ShutdownHookManager
> ---------------------------------------------------------------------------------------
>
>                 Key: HDFS-8896
>                 URL: https://issues.apache.org/jira/browse/HDFS-8896
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: test
>            Reporter: Walter Su
>            Assignee: Walter Su
>            Priority: Minor
>             Fix For: 2.8.0
>
>         Attachments: HDFS-8896.01.patch, screenshot_1.PNG, screenshot_2.PNG
>
>
> The anonymous {{Thread}} object created in {{ShutdownHookManager}} is a GC 
> root.
> screenshot_1 shows how DN object be traced to the GC root.
> It's not a problem in production.
> It's a problem in test, especially when MiniDFSCluster starts/shutdowns many 
> DNs, which could cause {{OutOfMemoryError}}.
> screenshot_2 shows many DN objects are not GCed when run the test of 
> HDFS-8838.



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