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https://issues.apache.org/jira/browse/HADOOP-5890?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12712637#action_12712637
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dhruba borthakur commented on HADOOP-5890:
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+1. Code looks good. 

> Use exponential backoff on Thread.sleep during DN shutdown
> ----------------------------------------------------------
>
>                 Key: HADOOP-5890
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5890
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hadoop-5890.txt
>
>
> Tests waste a lot of time in DataNode.shutdown. Typical logs look like:
> {code}
> 2009-05-21 17:13:20,177 INFO  datanode.DataNode (DataNode.java:shutdown(637)) 
> - Waiting for threadgroup to exit, active threads is 0
> 2009-05-21 17:13:20,177 INFO  datanode.DataBlockScanner 
> (DataBlockScanner.java:run(620)) - Exiting DataBlockScanner thread.
> 2009-05-21 17:13:21,117 INFO  datanode.DataNode (DataNode.java:shutdown(637)) 
> - Waiting for threadgroup to exit, active threads is 0
> {code}
> In this example (and very commonly) the DataBlockScanner thread exits within 
> 5-10ms after the first wait. The DN then sleeps an entire second before 
> succeeding in shutting down.
> Using exponential backoff from a short value like 2ms up to a maximum of 
> 1000ms would solve this.

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