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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1606) Provide a stronger data guarantee in the write pipeline
Date Wed, 06 Apr 2011 18:13:06 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13016472#comment-13016472

Tsz Wo (Nicholas), SZE commented on HDFS-1606:

- In [build #318|https://hudson.apache.org/hudson/job/PreCommit-HDFS-Build/318//testReport/org.apache.hadoop.hdfs/TestMultiThreadedHflush/testHflushWhileClosing/],
	at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.access$2500(DFSOutputStream.java:283)
	at org.apache.hadoop.hdfs.DFSOutputStream.hflush(DFSOutputStream.java:1470)
	at org.apache.hadoop.fs.FSDataOutputStream.hflush(FSDataOutputStream.java:110)
	at org.apache.hadoop.hdfs.TestMultiThreadedHflush$1.run(TestMultiThreadedHflush.java:156)
There are some existing synchronization problem in {{DFSOutputStream}}.  It is possible the
call {{hflush()}} after {{close()}} without getting any error.
I will simply check null in this patch.  Will think about the synchronization problem after

- For the other failed tests, it is simply not enough datanodes so that addDatanode failed.

> Provide a stronger data guarantee in the write pipeline
> -------------------------------------------------------
>                 Key: HDFS-1606
>                 URL: https://issues.apache.org/jira/browse/HDFS-1606
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: data-node, hdfs client, name-node
>    Affects Versions: 0.23.0
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>             Fix For: 0.23.0
>         Attachments: h1606_20110210.patch, h1606_20110211.patch, h1606_20110217.patch,
h1606_20110228.patch, h1606_20110404.patch, h1606_20110405.patch, h1606_20110405b.patch
> In the current design, if there is a datanode/network failure in the write pipeline,
DFSClient will try to remove the failed datanode from the pipeline and then continue writing
with the remaining datanodes.  As a result, the number of datanodes in the pipeline is decreased.
 Unfortunately, it is possible that DFSClient may incorrectly remove a healthy datanode but
leave the failed datanode in the pipeline because failure detection may be inaccurate under
erroneous conditions.
> We propose to have a new mechanism for adding new datanodes to the pipeline in order
to provide a stronger data guarantee.

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