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https://issues.apache.org/jira/browse/HDFS-3703?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13420795#comment-13420795
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Suresh Srinivas commented on HDFS-3703:
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bq. Globally, it would be ideal if HDFS settings could be under HBase settings.
Can you describe this better?
bq. HBase relies on ZooKeeper to detect regionservers issues
Whether ZooKeeper or Datanode heartbeat to Namenode, at a high level mechanisms
are similar. The problem is one of choosing right timeout. Currently this is
configurable in HDFS and 10 minutes is chosen as the timeout. I suggest running
some experiments with setting this to a more aggressive value. I agree that
this is a very conservative time. But false positives here could result in
replication storm.
> Decrease the datanode failure detection time
> --------------------------------------------
>
> Key: HDFS-3703
> URL: https://issues.apache.org/jira/browse/HDFS-3703
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: data-node, name-node
> Affects Versions: 1.0.3, 2.0.0-alpha
> Reporter: nkeywal
>
> By default, if a box dies, the datanode will be marked as dead by the
> namenode after 10:30 minutes. In the meantime, this datanode will still be
> proposed by the nanenode to write blocks or to read replicas. It happens as
> well if the datanode crashes: there is no shutdown hooks to tell the nanemode
> we're not there anymore.
> It especially an issue with HBase. HBase regionserver timeout for production
> is often 30s. So with these configs, when a box dies HBase starts to recover
> after 30s and, while 10 minutes, the namenode will consider the blocks on the
> same box as available. Beyond the write errors, this will trigger a lot of
> missed reads:
> - during the recovery, HBase needs to read the blocks used on the dead box
> (the ones in the 'HBase Write-Ahead-Log')
> - after the recovery, reading these data blocks (the 'HBase region') will
> fail 33% of the time with the default number of replica, slowering the data
> access, especially when the errors are socket timeout (i.e. around 60s most
> of the time).
> Globally, it would be ideal if HDFS settings could be under HBase settings.
> As a side note, HBase relies on ZooKeeper to detect regionservers issues.
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