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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8896) DataNode object isn't GCed when shutdown, because it has GC root in ShutdownHookManager
Date Thu, 27 Aug 2015 03:59:46 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14716041#comment-14716041
] 

Hudson commented on HDFS-8896:
------------------------------

FAILURE: Integrated in Hadoop-Hdfs-trunk #2237 (See [https://builds.apache.org/job/Hadoop-Hdfs-trunk/2237/])
HDFS-8896. DataNode object isn't GCed when shutdown, because it has GC root in ShutdownHookManager.
Contributed by Walter Su. (jing9: rev f44b599003bb79b1ec9b92e7546546523ec01676)
* hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/ShutdownHookManager.java
* hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
* hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/MiniDFSCluster.java


> 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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