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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1325) DFSClient(DFSInputStream) release the persistent connection with datanode when no data have been read for a long time
Date Thu, 05 Aug 2010 21:58:19 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895834#action_12895834
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Tsz Wo (Nicholas), SZE commented on HDFS-1325:
----------------------------------------------

> ... As a distribute system, we should keep service, right ?

You are right.  But the one-new-thread per DFSInputStream solution will really kill the system.
 If we can fix it with a lightweight solution, we could do it.

> DFSClient(DFSInputStream) release the persistent connection with datanode when no data
have been read for a long time
> ---------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1325
>                 URL: https://issues.apache.org/jira/browse/HDFS-1325
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>            Reporter: jinglong.liujl
>             Fix For: 0.20.3
>
>         Attachments: dfsclient.patch, toomanyconnction.patch
>
>
> When you use Hbase over hadoop. We found during scanning over a large table ( which has
many regions and each region has many store files), there're too many connections has been
kept between regionserver (act as DFSClient) and datanode.  Even if the store file has been
complete to scanning, the connections can not be closed.
> In our cluster, too many extra connections cause too many system resource has been wasted,
which cause system cpu on region server reach to a high level, then bring this region server
down.
> After investigating, we found the number of active connection is very small, and the
most connection is idle. We add a timeout checker thread into DFSClient, to close this connection.

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