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From Harsh J <ha...@cloudera.com>
Subject Re: ReplicationTargetChooser has incorrect block placement comments
Date Thu, 04 Apr 2013 06:14:33 GMT
Hi Mei,

These questions are best fit for the whole hdfs-dev@ group, which am
adding while responding back.

You're correct that the local node being not chosen, a random node on
the same rack as the writer may be tried. However, if the writer node
itself had no local DN in the first place, a completely random node
across any rack may be selected.

This is visible at

On Thu, Apr 4, 2013 at 12:53 AM, Mei Long <longmi@gmail.com> wrote:
> Hi Harsh,
> I found your post on JIRA regarding the comments. I find them very confusing
> as well. I'm trying to figure out the following comment:
>  * the 1st replica is placed on the local machine,
>  * otherwise a random datanode.
> Do you know when it says "otherwise a random datanode," does it mean any
> random datanode anywhere on the network or a random datanode on the same
> rack as the local machine? I've been looking at the code for an hour and I'm
> getting more confused with the comment and code in chooseLocalNode()
>   /* choose <i>localMachine</i> as the target.
>    * if <i>localMachine</i> is not availabe,
>    * choose a node on the same rack
>    * @return the choosen node
>    */
> Your help is much appreciated!
> Mei

Harsh J

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