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https://issues.apache.org/jira/browse/HDFS-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15205079#comment-15205079
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Tsz Wo Nicholas Sze commented on HDFS-3702:
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> So, the suggestion is changing public signatures to add a new parameter (Or
> adding a new override where there are already 6)?
For compatibility reason, we probably have to add a new override. For better
usability, we may add a Builder.
> For a client to make effective use of disfavoredNodes, they would have to
> figure the exact name the NN is using and volunteer it in this
> disfavoredNodes list? Or could they just write 'localhost' and let NN figure
> it out?
We should support 'localhost' in the API. DFSClient or NN may replace
'localhost' with the corresponding name.
> Do you foresee any other use for this disfavoredNodes parameter other than
> for the exclusion of 'localnode'?
Yes, disfavoredNodes seems useful. For example, some application may want to
distribute its files uniformly in a cluster. Then, it could specify the
previously allocated DNs as the disfavoredNodes.
> Add an option for NOT writing the blocks locally if there is a datanode on
> the same box as the client
> -----------------------------------------------------------------------------------------------------
>
> Key: HDFS-3702
> URL: https://issues.apache.org/jira/browse/HDFS-3702
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: hdfs-client
> Affects Versions: 2.5.1
> Reporter: Nicolas Liochon
> Assignee: Lei (Eddy) Xu
> Priority: Minor
> Labels: BB2015-05-TBR
> Attachments: HDFS-3702.000.patch, HDFS-3702.001.patch,
> HDFS-3702.002.patch, HDFS-3702.003.patch, HDFS-3702.004.patch,
> HDFS-3702.005.patch, HDFS-3702.006.patch, HDFS-3702.007.patch,
> HDFS-3702.008.patch, HDFS-3702_Design.pdf
>
>
> This is useful for Write-Ahead-Logs: these files are writen for recovery
> only, and are not read when there are no failures.
> Taking HBase as an example, these files will be read only if the process that
> wrote them (the 'HBase regionserver') dies. This will likely come from a
> hardware failure, hence the corresponding datanode will be dead as well. So
> we're writing 3 replicas, but in reality only 2 of them are really useful.
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