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https://issues.apache.org/jira/browse/HDFS-15304?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Istvan Fajth reassigned HDFS-15304:
-----------------------------------
Assignee: Istvan Fajth
> Infinite loop between DN and NN at rare condition
> -------------------------------------------------
>
> Key: HDFS-15304
> URL: https://issues.apache.org/jira/browse/HDFS-15304
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Istvan Fajth
> Assignee: Istvan Fajth
> Priority: Minor
>
> During the investigation lead to HDFS-15303, we have identified the following
> infinite loop between the DNs affected by the data directory layout problem:
> - for a particular misplaced block, the VolumeScanner finds the block file,
> and realizes that it is not part of the block map
> - the block is added to the block map
> - at the next FBR the block is reported to the NN
> - the NN finds that the block should have been deleted already, as the
> corresponding inode was already deleted
> - NN issues the deletion of the block on the DataNode
> - DataNode runs the delete routine, but that fails to delete anything
> silently as it is trying to delete the block from the wrong internal subdir
> that is calculated based on the block id with a different algorythm.
> - block is removed from the blockmap
> - VolumeScanner finds the block again, and adds it back to the blockmap
> The problem can happen only when there is a mixed layout on the DataNode due
> to some issue, and there are blocks in a subdir correct according to Hadoop2
> format, but the DN is already hadoop3, or vice versa if the problematic
> layout born during a rollback.
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