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https://issues.apache.org/jira/browse/HDFS-1921?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matt Foley resolved HDFS-1921.
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Resolution: Fixed
> Save namespace can cause NN to be unable to come up on restart
> --------------------------------------------------------------
>
> Key: HDFS-1921
> URL: https://issues.apache.org/jira/browse/HDFS-1921
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 0.22.0, 0.23.0
> Reporter: Aaron T. Myers
> Assignee: Matt Foley
> Priority: Blocker
> Fix For: 0.22.0, 0.23.0
>
> Attachments: hdfs-1505-1-test.txt, hdfs-1921-2.patch,
> hdfs-1921-2_v22.patch, hdfs-1921.txt, hdfs1921_v23.patch, hdfs1921_v23.patch
>
>
> I discovered this in the course of trying to implement a fix for HDFS-1505.
> Per the comment for {{FSImage.saveNamespace(...)}}, the algorithm for save
> namespace proceeds in the following order:
> # rename current to lastcheckpoint.tmp for all of them,
> # save image and recreate edits for all of them,
> # rename lastcheckpoint.tmp to previous.checkpoint.
> The problem is that step 3 occurs regardless of whether or not an error
> occurs for all storage directories in step 2. Upon restart, the NN will see
> non-existent or corrupt {{current}} directories, and no
> {{lastcheckpoint.tmp}} directories, and so will conclude that the storage
> directories are not formatted.
> This issue appears to be present on both 0.22 and 0.23. This should arguably
> be a 0.22/0.23 blocker.
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