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https://issues.apache.org/jira/browse/HDFS-8855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14692805#comment-14692805
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Bob Hansen commented on HDFS-8855:
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Does 2200 DN->NN connections seem a bit... excessive... for 50 concurrent
reads? If you set the concurrent_reads environment variable to 500, do you end
up with 22000 connections (and start running the NN out of ports very quickly)?
If the load scales up linearly with the cluster size (a process on each node
reading 50 files), will your NN run out of ports and fail?
> 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
> Environment: HDP 2.2
> Reporter: Bob Hansen
> Assignee: Xiaobing Zhou
>
> 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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