[HDFS-8896] DataNode object isn't GCed when shutdown, because it has GC root in ShutdownHookManager

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.8.0, 3.0.0-alpha1
• Component/s: test
• Hadoop Flags: Reviewed
• Assignee: Walter Su
• Reporter: Walter Su
• Created: 14/Aug/15 10:24
• Updated: 30/Aug/16 01:29
• Resolved: 26/Aug/15 23:47

Description

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.

Issue Links

• is related to: HDFS-8838 Erasure Coding: Tolerate datanode failures in DFSStripedOutputStream when the data length is small
• relates to: HADOOP-12261 Surefire needs to make sure the JVMs it fires up fit within the memory available