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From RJ Nowling <rnowl...@gmail.com>
Subject Re: Data Locality and WebHDFS
Date Mon, 17 Mar 2014 04:18:56 GMT
Thank you, Mingjiang and Alejandro.

This is interesting.  Since we will use the data locality information for
scheduling, we could "hack" this to get the data locality information, at
least for the first block.  As Alejandro says, we'd have to test what
happens for other data blocks -- e.g., what if, knowing the block sizes, we
request the second or third block?

Interesting food for thought!  I see some experiments in my future!

Thanks!


On Sun, Mar 16, 2014 at 10:14 PM, Alejandro Abdelnur <tucu@cloudera.com>wrote:

> well, this is for the first block of the file, the rest of the file
> (blocks being local or not) are streamed out by the same datanode. for
> small files (one block) you'll get locality, for large files only the first
> block, and by chance if other blocks are local to that datanode.
>
>
> Alejandro
> (phone typing)
>
> On Mar 16, 2014, at 18:53, Mingjiang Shi <mshi@gopivotal.com> wrote:
>
> According to this page:
> http://hortonworks.com/blog/webhdfs-%E2%80%93-http-rest-access-to-hdfs/
>
>> *Data Locality*: The file read and file write calls are redirected to
>> the corresponding datanodes. It uses the full bandwidth of the Hadoop
>> cluster for streaming data.
>>
>> *A HDFS Built-in Component*: WebHDFS is a first class built-in component
>> of HDFS. It runs inside Namenodes and Datanodes, therefore, it can use all
>> HDFS functionalities. It is a part of HDFS - there are no additional
>> servers to install
>>
>
> So it looks like the data locality is built-into webhdfs, client will be
> redirected to the data node automatically.
>
>
>
>
> On Mon, Mar 17, 2014 at 6:07 AM, RJ Nowling <rnowling@gmail.com> wrote:
>
>> Hi all,
>>
>> I'm writing up a Google Summer of Code proposal to add HDFS support to
>> Disco, an Erlang MapReduce framework.
>>
>> We're interested in using WebHDFS.  I have two questions:
>>
>> 1) Does WebHDFS allow querying data locality information?
>>
>> 2) If the data locality information is known, can data on specific data
>> nodes be accessed via Web HDFS?  Or do all Web HDFS requests have to go
>> through a single server?
>>
>> Thanks,
>> RJ
>>
>> --
>> em rnowling@gmail.com
>> c 954.496.2314
>>
>
>
>
> --
> Cheers
> -MJ
>
>


-- 
em rnowling@gmail.com
c 954.496.2314

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