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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6701) Make seed optional in NetworkTopology#sortByDistance
Date Fri, 18 Jul 2014 17:36:05 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6701?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14066575#comment-14066575
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Andrew Wang commented on HDFS-6701:
-----------------------------------

Hi Ashwin, thanks for working on this. Overall looks good, a few nitty things:

Unnecessary whitespace change:
{code}
+   // If reader is not a datanode (not in NetworkTopology tree), we need to
{code}

* hdfs-default.xml property needs some more explanation, e.g. explain the default behavior,
why/when you might want to enable this new config
* Could you also check this applies to branch-2 patch? IIRC branch-2 has an additional test
file that needs to be modified, so we might need a branch-2 patch.


> Make seed optional in NetworkTopology#sortByDistance
> ----------------------------------------------------
>
>                 Key: HDFS-6701
>                 URL: https://issues.apache.org/jira/browse/HDFS-6701
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.5.0
>            Reporter: Ashwin Shankar
>         Attachments: HDFS-6701-v1.txt
>
>
> Currently seed in NetworkTopology#sortByDistance is set to the blockid which causes the
RNG to generate same pseudo random order for each block. If no node local block location is
present,this causes the same rack local replica to be hit for a particular block.
> It'll be good to make the seed optional, so that one could turn it off if they want block
locations of a block to be randomized.



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