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Date: Tue, 28 Jan 2014 12:01:50 -0800
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 <CADdVdVEMcQ6yt7dfz4ozf0kPM7Rk5OmXYCZ2Zv0g-1bn3mQseA@mail.gmail.com>
Subject: Re: HDFS Federation address performance issue
From: Suresh Srinivas <suresh@hortonworks.com>
To: "hdfs-user@hadoop.apache.org" <user@hadoop.apache.org>
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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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<div dir=3D"ltr">Response inline...<br><div class=3D"gmail_extra"><br><br><=
div class=3D"gmail_quote">On Tue, Jan 28, 2014 at 10:04 AM, Anfernee Xu <sp=
an dir=3D"ltr">&lt;<a href=3D"mailto:anfernee.xu@gmail.com" target=3D"_blan=
k">anfernee.xu@gmail.com</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-=
left:1px solid rgb(204,204,204);padding-left:1ex"><div dir=3D"ltr"><div><di=
v><div><div>Hi,<br><br></div>Based on <a href=3D"http://hadoop.apache.org/d=
ocs/stable/hadoop-project-dist/hadoop-hdfs/Federation.html#Key_Benefits" ta=
rget=3D"_blank">http://hadoop.apache.org/docs/stable/hadoop-project-dist/ha=
doop-hdfs/Federation.html#Key_Benefits</a>, the overall performance can be =
improved by federation, but I&#39;m not sure federation address my usercase=
, could someone elaborate it?<br>

<br></div>My usercase is I have one single NM and several DN, and I have bu=
nch of concurrent MR jobs which will create new files(plan files and sub-di=
rectory) under the same parent directory, the questions are:<br><br>1) Will=
 these concurrent writes(new file, plan files and sub-directory under the s=
ame parent directory) run in sequential because WRITE-once control govened =
by single NM?<br>
</div></div></div></blockquote><div><br></div><div>Namenode commits multipl=
e requests in a batch. In Namenode it self, the lock for write operations m=
ake them sequential. But this is a short duration lock and hence will make =
from the multiple clients perspective, the creation of files as simultaneou=
s.<br>
<br></div><div>If you are talking about a single client, with a single thre=
ad, then it would be sequential.<br><br>Hope that makes sense.<br></div><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-lef=
t:1px solid rgb(204,204,204);padding-left:1ex">
<div dir=3D"ltr"><div><div>
<br></div>I need this answer to estimate the necessity of moving to HDFS fe=
deration.<br><br></div>Thanks<span class=3D""><font color=3D"#888888"><br><=
div><div><div><div><div><br>-- <br>--Anfernee
</div></div></div></div></div></font></span></div>
</blockquote></div><br><br clear=3D"all"><br>-- <br><a> http://hortonworks.=
com/download/</a><br>
</div></div>

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