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https://issues.apache.org/jira/browse/HDFS-12703?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16850261#comment-16850261
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Xue Liu commented on HDFS-12703:
--------------------------------
Hi the exception I found come from check():
{code:java}
Preconditions.checkState(false, "A node is in an invalid state!")
{code}
This will cause exception and the way executor#scheduleAtFixedRate works, the
thread's further execution will be suppressed.
So I just add exception handle to prevent exception killing the decommission,
and add a few logs to help with debugging.
It is not clear why sometimes DNs will be in a erroneous state, but this change
will unblock the thread and allow us dig further.
> Exceptions are fatal to decommissioning monitor
> -----------------------------------------------
>
> Key: HDFS-12703
> URL: https://issues.apache.org/jira/browse/HDFS-12703
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.7.0
> Reporter: Daryn Sharp
> Assignee: Xue Liu
> Priority: Critical
> Attachments: HDFS-12703.001.patch
>
>
> The {{DecommissionManager.Monitor}} runs as an executor scheduled task. If
> an exception occurs, all decommissioning ceases until the NN is restarted.
> Per javadoc for {{executor#scheduleAtFixedRate}}: *If any execution of the
> task encounters an exception, subsequent executions are suppressed*. The
> monitor thread is alive but blocked waiting for an executor task that will
> never come. The code currently disposes of the future so the actual
> exception that aborted the task is gone.
> Failover is insufficient since the task is also likely dead on the standby.
> Replication queue init after the transition to active will fix the under
> replication of blocks on currently decommissioning nodes but future nodes
> never decommission. The standby must be bounced prior to failover – and
> hopefully the error condition does not reoccur.
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