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Date: Fri, 14 Aug 2015 10:24:45 +0000 (UTC)
From: "Walter Su (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
Message-ID: <JIRA.12856122.1439547863000.66222.1439547885676@Atlassian.JIRA>
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Subject: [jira] [Created] (HDFS-8896) DataNode object isn't GCed when
 shutdown, because it has GC root in ShutdownHookManager
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Walter Su created HDFS-8896:
-------------------------------

             Summary: 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


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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