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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-988) saveNamespace can corrupt edits log, apparently due to race conditions
Date Wed, 01 Jun 2011 03:29:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13041962#comment-13041962
] 

dhruba borthakur commented on HDFS-988:
---------------------------------------

we should not logSync after a nextGenerationStamp() because it is invoked for every file creation,
isn't it? and before the file-create call returns from the NN, we do invoke logSync(), so
we shud be safe.

The other time we invoke nextGenerationStamp() is for pipeline error recovery, and that code
path should also be ok, let me think.

> saveNamespace can corrupt edits log, apparently due to race conditions
> ----------------------------------------------------------------------
>
>                 Key: HDFS-988
>                 URL: https://issues.apache.org/jira/browse/HDFS-988
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: name-node
>    Affects Versions: 0.20-append, 0.21.0, 0.22.0
>            Reporter: dhruba borthakur
>            Assignee: Eli Collins
>            Priority: Blocker
>             Fix For: 0.20-append, 0.22.0
>
>         Attachments: HDFS-988_fix_synchs.patch, hdfs-988-2.patch, hdfs-988-3.patch, hdfs-988-4.patch,
hdfs-988.txt, saveNamespace.txt, saveNamespace_20-append.patch
>
>
> The adminstrator puts the namenode is safemode and then issues the savenamespace command.
This can corrupt the edits log. The problem is that  when the NN enters safemode, there could
still be pending logSycs occuring from other threads. Now, the saveNamespace command, when
executed, would save a edits log with partial writes. I have seen this happen on 0.20.
> https://issues.apache.org/jira/browse/HDFS-909?focusedCommentId=12828853&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12828853

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