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From "jinglong.liujl (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 Sun, 15 Aug 2010 12:34:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12898691#action_12898691

jinglong.liujl commented on HDFS-1325:

Sorry for late reply.
>Inspite of this, if you feel that this is the way you want to solve the problem, please
consider adding this check into the application layer code, instead of DFSClient.
   I think the solution should not only close() file on application. 
   Absolutely, in application layer (like HBase), It must release resource (like FSDataOutputStream,
connection...). On the other hand, even if application (hbase) has not release resource, hadoop
which act as a cloud platform should not out of service, it should release these resource
and keep provide service to other applications. 
   Thus, some final way should be existed to release idle resource. And this patch is just
this final way.
> 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.
You're right, I'll make some revision on 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
> 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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