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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5796) DFS Write pipeline does not detect defective datanode correctly in some cases (HADOOP-3339)
Date Tue, 24 Nov 2009 23:31:39 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12782237#action_12782237
] 

Todd Lipcon commented on HADOOP-5796:
-------------------------------------

Silly me, now I see that this patch is just to reproduce, not to fix :) Will investigate a
fix since I have a good petri dish in which to reproduce this issue.

> DFS Write pipeline does not detect defective datanode correctly in some cases (HADOOP-3339)
> -------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-5796
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5796
>             Project: Hadoop Common
>          Issue Type: Bug
>    Affects Versions: 0.19.0
>            Reporter: Raghu Angadi
>             Fix For: 0.20.2
>
>         Attachments: toreproduce-5796.patch
>
>
> HDFS write pipeline does not select the correct datanode in some error cases. One example
: say DN2 is the second datanode and write to it times out since it is in a bad state.. pipeline
actually removes the first datanode. If such a datanode happens to be the last one in the
pipeline, write is aborted completely with a hard error.
> Essentially the error occurs when writing to a downstream datanode fails rather than
reading. This bug was actually fixed in 0.18 (HADOOP-3339). But HADOOP-1700 essentially reverted
it. I am not sure why.
> It is absolutely essential for HDFS to handle failures on subset of datanodes in a pipeline.
We should not have at least known bugs that lead to hard failures.
> I will attach patch for a hack that illustrates this problem. Still thinking of how an
automated test would look like for this one. 
> My preferred target for  this fix is 0.20.1.

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