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https://issues.apache.org/jira/browse/HDFS-4596?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13602640#comment-13602640
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Aaron T. Myers commented on HDFS-4596:
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+1, the patch looks good to me. I'm going to commit this momentarily.
> Shutting down namenode during checkpointing can lead to md5sum error
> --------------------------------------------------------------------
>
> Key: HDFS-4596
> URL: https://issues.apache.org/jira/browse/HDFS-4596
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 3.0.0, 2.0.4-alpha
> Reporter: Andrew Wang
> Assignee: Andrew Wang
> Attachments: hdfs-4596-1.patch
>
>
> This is a really rare error that can hit if a NN shutdown happens during the
> checkpointing process.
> Checkpointing and restarting nominally looks like this:
> # FSImage is written to a tmp file and then renamed
> # MD5 file is written to a tmp file and then renamed
> # NN is killed and restarted
> # NN scans storage directories and picks up the renamed image file
> # NN validates that the image file matches its md5 file
> If the NN is killed before step 2 completes, this is what happens:
> # FSImage is written to a tmp file and then renamed
> # NN is killed and restarted (no MD5 file!)
> # NN scans storage directories and picks up the renamed image file
> # Since there's no matching MD5 file, NN errors out with a checksum error
> I think we can fix this by inverting the order of writing the image then md5,
> or inverting the order of reading the image then md5.
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