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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4739) NN can miscalculate the number of extra edit log segments to retain
Date Wed, 24 Apr 2013 21:21:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4739?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13640968#comment-13640968

Chris Nauroth commented on HDFS-4739:

+1 for the patch.  Nice catch, Aaron!

BTW, I also have a patch in {{TestNNStorageRetentionManager}} on HDFS-4743, but there is no
merge conflict.
> NN can miscalculate the number of extra edit log segments to retain
> -------------------------------------------------------------------
>                 Key: HDFS-4739
>                 URL: https://issues.apache.org/jira/browse/HDFS-4739
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>    Affects Versions: 2.0.4-alpha
>            Reporter: Aaron T. Myers
>            Assignee: Aaron T. Myers
>         Attachments: HDFS-4739.patch, HDFS-4739.patch
> The code in NNStorageRetentionManager#purgeOldStorage is intended to place a cap on the
number of _extra_ edit log segments retained beyond what is strictly required to replay the
FS history since the last fsimage. In fact this code currently places a limit on the _total_
number of extra edit log segments. If the number of required segments is greater than the
configured cap, there will be no data loss, but an ugly error will be thrown and the NN will
fail to start.
> The fix is simple, and in the meantime a work-around is just to raise the value of dfs.namenode.max.extra.edits.segments.retained
and start the NN.

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