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https://issues.apache.org/jira/browse/HDFS-8855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16731542#comment-16731542
]
Subham Mittal edited comment on HDFS-8855 at 1/1/19 8:45 AM:
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Check
[https://javahungry.blogspot.com/2013/08/singleton-design-pattern-use-in-java.html]
for a nice detail about idiomatic singletons in Java.
was (Author: harinder07):
See
[https://javahungry.blogspot.com/2013/08/singleton-design-pattern-use-in-java.html]
for a nice little discussion of idiomatic singletons in Java
> Webhdfs client leaks active NameNode connections
> ------------------------------------------------
>
> Key: HDFS-8855
> URL: https://issues.apache.org/jira/browse/HDFS-8855
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: webhdfs
> Reporter: Bob Hansen
> Assignee: Xiaobing Zhou
> Priority: Major
> Fix For: 2.8.0, 3.0.0-alpha1
>
> Attachments: HDFS-8855.005.patch, HDFS-8855.006.patch,
> HDFS-8855.007.patch, HDFS-8855.008.patch, HDFS-8855.009.patch,
> HDFS-8855.1.patch, HDFS-8855.2.patch, HDFS-8855.3.patch, HDFS-8855.4.patch,
> HDFS_8855.prototype.patch
>
>
> The attached script simulates a process opening ~50 files via webhdfs and
> performing random reads. Note that there are at most 50 concurrent reads,
> and all webhdfs sessions are kept open. Each read is ~64k at a random
> position.
> The script periodically (once per second) shells into the NameNode and
> produces a summary of the socket states. For my test cluster with 5 nodes,
> it took ~30 seconds for the NameNode to have ~25000 active connections and
> fails.
> It appears that each request to the webhdfs client is opening a new
> connection to the NameNode and keeping it open after the request is complete.
> If the process continues to run, eventually (~30-60 seconds), all of the
> open connections are closed and the NameNode recovers.
> This smells like SoftReference reaping. Are we using SoftReferences in the
> webhdfs client to cache NameNode connections but never re-using them?
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