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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 Wed, 04 Aug 2010 17:38:17 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12895328#action_12895328
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Tsz Wo (Nicholas), SZE commented on HDFS-1325:
----------------------------------------------

> As a platform, we should handle these resources to make platform more robust, right ?


Yes.  Following from this direction, we probably should limit the number of open files, like
the file descriptor limit in Unix.

In the patch, a new TimeoutChecker thread is started for each DFSInputStream.  It is very
expensive.  All clients, idle or not, have to pay for 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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