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From Suresh Srinivas <sur...@hortonworks.com>
Subject Re: HDFS Federation address performance issue
Date Tue, 28 Jan 2014 20:01:50 GMT
Response inline...


On Tue, Jan 28, 2014 at 10:04 AM, Anfernee Xu <anfernee.xu@gmail.com> wrote:

> Hi,
>
> Based on
> http://hadoop.apache.org/docs/stable/hadoop-project-dist/hadoop-hdfs/Federation.html#Key_Benefits,
> the overall performance can be improved by federation, but I'm not sure
> federation address my usercase, could someone elaborate it?
>
> My usercase is I have one single NM and several DN, and I have bunch of
> concurrent MR jobs which will create new files(plan files and
> sub-directory) under the same parent directory, the questions are:
>
> 1) Will these concurrent writes(new file, plan files and sub-directory
> under the same parent directory) run in sequential because WRITE-once
> control govened by single NM?
>

Namenode commits multiple requests in a batch. In Namenode it self, the
lock for write operations make them sequential. But this is a short
duration lock and hence will make from the multiple clients perspective,
the creation of files as simultaneous.

If you are talking about a single client, with a single thread, then it
would be sequential.

Hope that makes sense.

>
> I need this answer to estimate the necessity of moving to HDFS federation.
>
> Thanks
>
> --
> --Anfernee
>



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