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https://issues.apache.org/jira/browse/HDFS-16565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17565256#comment-17565256
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Wei-Chiu Chuang commented on HDFS-16565:
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For future reference, i highly recommend using this tool to detect file
descriptor leak/socket leak: https://file-leak-detector.kohsuke.org/
Or more generally, use ByteMan or BTrace.
> DataNode holds a large number of CLOSE_WAIT connections that are not released
> -----------------------------------------------------------------------------
>
> Key: HDFS-16565
> URL: https://issues.apache.org/jira/browse/HDFS-16565
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode, ec
> Affects Versions: 3.3.0
> Environment: CentOS Linux release 7.5.1804 (Core)
> Reporter: JiangHua Zhu
> Priority: Major
> Attachments: screenshot-1.png, screenshot-2.png
>
>
> There is a strange phenomenon here, DataNode holds a large number of
> connections in CLOSE_WAIT state and does not release.
> netstat -na | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
> LISTEN 20
> CLOSE_WAIT 17707
> ESTABLISHED 1450
> TIME_WAIT 12
> It can be found that the connections with the CLOSE_WAIT state have reached
> 17k and are still growing. View these CLOSE_WAITs through the lsof command,
> and get the following phenomenon:
> lsof -i tcp | grep -E 'CLOSE_WAIT|COMMAND'
> !screenshot-1.png!
> It can be seen that the reason for this phenomenon is that Socket#close() is
> not called correctly, and DataNode interacts with other nodes as Client.
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