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Date: Thu, 24 Jun 2010 19:55:50 -0400 (EDT)
From: "sam rash (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-1186) 0.20: DNs should interrupt writers at
 start of recovery
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    [ https://issues.apache.org/jira/browse/HDFS-1186?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882401#action_12882401 ] 

sam rash commented on HDFS-1186:
--------------------------------

hmm i wonder why only 1?  if the client thinks there are 3 DNs in the pipeline and asks to recovery 3, i think it should fail with less than 3.  a client can request fewer if that works (in which case we do have to handle the problem you lay out)

so in your sol'n, you are saying that the lease holder, the client, needs to be contacted to verify the primary is the only one doing lease recovery? (or at least the latest)


> 0.20: DNs should interrupt writers at start of recovery
> -------------------------------------------------------
>
>                 Key: HDFS-1186
>                 URL: https://issues.apache.org/jira/browse/HDFS-1186
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.20-append
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Blocker
>         Attachments: hdfs-1186.txt
>
>
> When block recovery starts (eg due to NN recovering lease) it needs to interrupt any writers currently writing to those blocks. Otherwise, an old writer (who hasn't realized he lost his lease) can continue to write+sync to the blocks, and thus recovery ends up truncating data that has been sync()ed.

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