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From "Xiaobing Zhou (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8855) Webhdfs client leaks active NameNode connections
Date Wed, 12 Aug 2015 00:33:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8855?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14692650#comment-14692650
] 

Xiaobing Zhou commented on HDFS-8855:
-------------------------------------

Tested HDFS-7597 patch, it’s working well for HDFS-8855.  In my 3 nodes of local VMs, the
ESTABLISHED connection varies from 1400 to 2200 as load generator is running.
The code path is different in two cases. HDFS-8855 case goes to cache in org.apache.hadoop.ipc.connection.
Let’s investigate on that cache.

> 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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