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From "Eli Collins (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-988) saveNamespace can corrupt edits log, apparently due to race conditions
Date Wed, 01 Jun 2011 18:33:47 GMT

    [ https://issues.apache.org/jira/browse/HDFS-988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13042351#comment-13042351
] 

Eli Collins commented on HDFS-988:
----------------------------------

It looks like most of the unprotected* methods take the rwlock, but don't need to because
either because their caller takes the lock or they are called from loading the edit log (which
is why we originally had unprotected versions). Do people mind if I fix that up (remove the
locking from these methods, make sure the unprotected versions are only called when loading
the log) in this change or do people want that done in a separate change?

> 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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