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https://issues.apache.org/jira/browse/HDFS-3705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13428105#comment-13428105
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Suresh Srinivas commented on HDFS-3705:
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If no one gets to this before me, I will review this patch early next week.
> Add the possibility to mark a node as 'low priority' for read in the DFSClient
> ------------------------------------------------------------------------------
>
> Key: HDFS-3705
> URL: https://issues.apache.org/jira/browse/HDFS-3705
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs client
> Affects Versions: 1.0.3, 2.0.0-alpha
> Reporter: nkeywal
> Attachments: hdfs-3705.sample.patch
>
>
> This has been partly discussed in HBASE-6435.
> The DFSClient includes a 'bad nodes' management for reads and writes.
> Sometimes, the client application already know that some deads are dead or
> likely to be dead.
> An example is the 'HBase Write-Ahead-Log': when HBase reads this file, it
> knows that the HBase regionserver died, and it's very likely that the box
> died so the datanode on the same box is dead as well. This is actually
> critical, because:
> - it's the hbase recovery that reads these log files
> - if we read them it means that we lost a box, so we have 1 dead replica out
> the the 3.
> - for all files read, we have 33% of chance to go to the dead datanode
> - as the box just died, we're very likely to get a timeout exception so we're
> delaying the hbase recovery by 1 minute. For HBase, it means that the data is
> not available during this minute.
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