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https://issues.apache.org/jira/browse/HDFS-7235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14186437#comment-14186437
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Yongjun Zhang commented on HDFS-7235:
-------------------------------------
There was TestDistributedShell failure reported as YARN-2607, the symptom there
looks a bit different than the one reported above. I ran the same test locally
before (trunk tip 5b1dfe78b8b06335bed0bcb83f12bb936d4c021b) and after the patc,
they failed the same way, but the symptom running locally is different than
YARN-2607, and the report above.
Seems this test need some more study, just uploaded the same patch here again
to see how it runs.
> DataNode#transferBlock should report blocks that don't exist using
> reportBadBlock
> ---------------------------------------------------------------------------------
>
> Key: HDFS-7235
> URL: https://issues.apache.org/jira/browse/HDFS-7235
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode, namenode
> Affects Versions: 2.6.0
> Reporter: Yongjun Zhang
> Assignee: Yongjun Zhang
> Attachments: HDFS-7235.001.patch, HDFS-7235.002.patch,
> HDFS-7235.003.patch, HDFS-7235.004.patch, HDFS-7235.005.patch,
> HDFS-7235.006.patch, HDFS-7235.007.patch, HDFS-7235.007.patch
>
>
> When to decommission a DN, the process hangs.
> What happens is, when NN chooses a replica as a source to replicate data on
> the to-be-decommissioned DN to other DNs, it favors choosing this DN
> to-be-decommissioned as the source of transfer (see BlockManager.java).
> However, because of the bad disk, the DN would detect the source block to be
> transfered as invalidBlock with the following logic in FsDatasetImpl.java:
> {code}
> /** Does the block exist and have the given state? */
> private boolean isValid(final ExtendedBlock b, final ReplicaState state) {
> final ReplicaInfo replicaInfo = volumeMap.get(b.getBlockPoolId(),
> b.getLocalBlock());
> return replicaInfo != null
> && replicaInfo.getState() == state
> && replicaInfo.getBlockFile().exists();
> }
> {code}
> The reason that this method returns false (detecting invalid block) is
> because the block file doesn't exist due to bad disk in this case.
> The key issue we found here is, after DN detects an invalid block for the
> above reason, it doesn't report the invalid block back to NN, thus NN doesn't
> know that the block is corrupted, and keeps sending the data transfer request
> to the same DN to be decommissioned, again and again. This caused an infinite
> loop, so the decommission process hangs.
> Thanks [~qwertymaniac] for reporting the issue and initial analysis.
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