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HDFS, mail # user - Can a jobtracker directly access datanode information (block placement) on namenode?


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Kyungyong Lee 2012-07-20, 20:36
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Re: Can a jobtracker directly access datanode information (block placement) on namenode?
Harsh J 2012-07-21, 03:54
Hi,

Any HDFS client can request a list of block locations for a given file
path (node-level detail of where blocks are placed for a file), via
the FileSystem#getFileBlockLocations API:
http://hadoop.apache.org/common/docs/current/api/org/apache/hadoop/fs/FileSystem.html#getFileBlockLocations(org.apache.hadoop.fs.FileStatus,%20long,%20long)

MR too gets this info via the user's InputFormat#getSplits method, and
schedules with these locations.

On Sat, Jul 21, 2012 at 2:06 AM, Kyungyong Lee <[EMAIL PROTECTED]> wrote:
> Hello all,
>
> I want to get datanode information (related to block placement) that is kept
> at a namenode from a jobtracker. As far as I understand, the jobtracker uses
> the locality-of-data for job scheduling, so I believe the jobtracker is
> keeping the information somewhere in the source code. However, I could not
> find the location. Can anyone give me a starting point (source code) where
> the jobtracker has access to block placement information? Thanks.
>

--
Harsh J