Istvan Fajth created HDFS-15304:
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Summary: 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
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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