FAQ
Null pointer exception is thrown when NN restarts with a block lesser in size than the block that is present in DN1 but the generation stamp is greater in the NN
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Key: HDFS-1982
URL: https://issues.apache.org/jira/browse/HDFS-1982
Project: Hadoop HDFS
Issue Type: Bug
Components: name-node
Affects Versions: 0.20-append
Environment: Linux
Reporter: ramkrishna.s.vasudevan
Fix For: 0.20-append


Conisder the following scenario.
WE have a cluster with one NN and 2 DN.

We write some file.

One of the block is written in DN1 but not yet completed in DN2 local disk.

Now DN1 gets killed and so pipeline recovery happens for the block with the size as in DN2 but the generation stamp gets updated in the NN.

DN2 also gets killed.

Now restart NN and DN1
Now if NN restarts, the block that NN has greater time stamp but the size is lesser in the NN.

This leads to Null pointer exception in addstoredblock api




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