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From "Lei (Eddy) Xu (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-3702) Add an option for NOT writing the blocks locally if there is a datanode on the same box as the client
Date Wed, 09 Mar 2016 00:31:41 GMT

     [ https://issues.apache.org/jira/browse/HDFS-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Lei (Eddy) Xu updated HDFS-3702:
--------------------------------
    Attachment: HDFS-3702.004.patch

Hey, [~andrew.wang]

Thanks for the suggestions. I change the patch to address your comments. The main idea is
that the client passes a {{NO_LOCAL_WRITE}} flag to {{BlockPlacementPolicy}}, which tries
excluding the local DN first. If no enough DN can be obtained, then {{BlockPlacementPolicy}}
falls back to the normal procedure. 

Would you take another look?

> 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
>
>
> 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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