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From "Bob Hansen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8855) Webhdfs client leaks active NameNode connections
Date Wed, 19 Aug 2015 18:18:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14703505#comment-14703505
] 

Bob Hansen commented on HDFS-8855:
----------------------------------

Agreed that the RPC cache not working is a bug that should be fixed independently.  It can
be argued that caching the whole client object is an additional optimization that has some
value here.

But yes, we should track down why the RPC cache is failing us.

> 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
>         Attachments: HDFS-8855.1.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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