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From "Andrzej Bialecki (JIRA)" <j...@apache.org>
Subject [jira] Created: (HADOOP-1046) Datanode should periodically clean up /tmp from partially received (and not completed) block files
Date Tue, 27 Feb 2007 18:58:05 GMT
Datanode should periodically clean up /tmp from partially received (and not completed) block
files
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                 Key: HADOOP-1046
                 URL: https://issues.apache.org/jira/browse/HADOOP-1046
             Project: Hadoop
          Issue Type: Bug
          Components: dfs
    Affects Versions: 0.9.2, 0.12.0
         Environment: Cluster of 10 machines, running Hadoop 0.9.2 + Nutch
            Reporter: Andrzej Bialecki 


Cluster is set up with tasktrackers running on the same machines as datanodes. Tasks create
heavy load in terms of local CPU/RAM/diskIO. I noticed a lot of the following messages from
the datanodes in such situations:

2007-02-15 05:30:53,298 WARN  dfs.DataNode - Failed to transfer blk_-4590782726923911824 to
xxx.xxx.xxx/10.10.16.109:50010
java.net.SocketException: Connection reset 
....
java.io.IOException: Block blk_71053993347675204 has already been started (though not completed),
and thus cannot be created. 

My reading of the code in DataNode.DataXceiver.writeBlock() and FSDataset.writeToBlock() +
FSDataset.java:459 suggests the following scenario: there is no cleanup of temporary files
in /tmp that are used to store the incomplete blocks being transferred. If the datanode is
CPU-starved and drops the connection while creating this temp file, the source datanode will
attempt to transfer it again - but there is already a file under this name in /tmp, because
when the connection was dropped the target datanode didn't bother to cleanup.

I also see that this section is unchanged in trunk/.

The solution to this would be to check the age of the physical file in the /tmp dir, in FSDataset.java:436
- if it's older than a few hours or so, we should delete it and proceed as if there were no
ongoing create op for this block.

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