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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-3702) Add an option for NOT writing the blocks locally if there is a datanode on the same box as the client
Date Sat, 09 Apr 2016 03:19:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15233324#comment-15233324
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Tsz Wo Nicholas Sze edited comment on HDFS-3702 at 4/9/16 3:18 AM:
-------------------------------------------------------------------

I suggest adding a new create(..) method to DistributedFileSystem, either with a new boolean
or with the AddBlockFlag, in this JIRA so that the community can try out the feature.  We
may add the CreateFlag.NO_LOCAL_WRITE once the feature has been stabilized and we has decided
that it is the right API.

As you mentioned, the favoredNodes turned out to be a not so good idea.  I am glad that it
was not added to the FileSystem API at that time.  Thanks.


was (Author: szetszwo):
I suggest adding a new create(..) method to DistributedFileSystem, either with a new boolean
or with the AddBlockFlag, in this JIRA so that the community can try out the feature.  We
may add the CreateFlag.NO_LOCAL_WRITE once the feature has been stabled and we has decided
that it the right API.

As you mentioned, the favoredNodes turned out to be a not so good idea.  I am glad that it
was not added to the FileSystem API at that time.

> 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-3702.009.patch, HDFS-3702.010.patch, HDFS-3702.011.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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