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https://issues.apache.org/jira/browse/HDFS-7235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14177518#comment-14177518
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Colin Patrick McCabe commented on HDFS-7235:
--------------------------------------------
{code}
1787 ReplicaInfo replicaInfo = null;
1788 synchronized(data) {
1789 replicaInfo = (ReplicaInfo) data.getReplica(
block.getBlockPoolId(),
1790 block.getBlockId());
1791 }
1792 if (replicaInfo != null
1793 && replicaInfo.getState() == ReplicaState.FINALIZED
1794 && !replicaInfo.getBlockFile().exists()) {
{code}
You can't release the lock this way. Once you release the lock, replicaInfo
could be mutated at any time. So you need to do all the check under the lock.
{code}
1795 //
1796 // Report back to NN bad block caused by non-existent block
file.
1797 // WATCH-OUT: be sure the conditions checked above matches the
following
1798 // method in FsDatasetImpl.java:
1799 // boolean isValidBlock(ExtendedBlock b)
1800 // all other conditions need to be true except that
1801 // replicaInfo.getBlockFile().exists() returns false.
1802 //
{code}
I don't think we need the "WATCH-OUT" part. We're not calling
{{isValidBlock}}, so why do we care if the check is the same as that check?
I generally agree with this approach and I think we can get this in if that's
fixed.
> Can not decommission DN which has invalid block due to bad disk
> ---------------------------------------------------------------
>
> 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
>
>
> 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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