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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8855) Webhdfs client leaks active NameNode connections
Date Wed, 04 Nov 2015 18:40:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14990134#comment-14990134
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Chris Nauroth commented on HDFS-8855:
-------------------------------------

HDFS-9370 has +1's from multiple committers and contributors now.  That one is ready.

> 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
>             Fix For: 2.8.0
>
>         Attachments: HDFS-8855.005.patch, HDFS-8855.006.patch, HDFS-8855.007.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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