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From "Nathan Roberts (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2825) Add test hook to turn off the writer preferring its local DN
Date Tue, 16 Dec 2014 19:20:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14248733#comment-14248733
] 

Nathan Roberts commented on HDFS-2825:
--------------------------------------

[~tlipcon] - It might help. I'm a little concerned about the additional round trip and how
we might enable it globally for an entire cluster. We'll be running some experiments with
a global config for the block placement policy, and then go from there.

> Add test hook to turn off the writer preferring its local DN
> ------------------------------------------------------------
>
>                 Key: HDFS-2825
>                 URL: https://issues.apache.org/jira/browse/HDFS-2825
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>            Priority: Minor
>             Fix For: 0.24.0, 0.23.1
>
>         Attachments: hdfs-2825.txt, hdfs-2825.txt
>
>
> Currently, the default block placement policy always places the first replica in the
pipeline on the local node if there is a valid DN running there. In some network designs,
within-rack bandwidth is never constrained so this doesn't give much of an advantage. It would
also be really useful to disable this for MiniDFSCluster tests, since currently if you start
a multi-DN cluster and write with replication level 1, all of the replicas go to the same
DN.
> _[per discussion below, this was changed to not add a config, but only to add a hook
for testing]_



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