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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 Tue, 03 Aug 2010 11:57:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1325?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12894870#action_12894870

jinglong.liujl commented on HDFS-1325:

     Thank you for your recommend.HDFS-941 can fix our issue.

     In fact, this timeout is a final way to release connection. For example, if user(dfsclient)
has not read data for 1 hour (currently, supposed timeout is a hour ), we can release the
connection between DFSClient and datanode. For idle user, platform can release the resource
which he request before.
     In our case, DFSClient request some data, and datanode will send a whole block(block
in HDFS) to client, the extra data is left in receive queue and send queue. In our cluster,
thousands of connections has been kept in region server, and socket memory has been over used.
so socket oom cause machine down. (from dmesg).
     This issue can be deal as duplicated bug. Thanks again.

> 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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