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Date: Tue, 18 Dec 2012 16:09:12 -0500
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 <CADokdcNxXbkVWidJD+k27WMQecHMK89wMQZtNYHZ==tObK+n+A@mail.gmail.com>
Subject: Re: datanode write forwarding
From: Chris Embree <cembree@gmail.com>
To: user@hadoop.apache.org
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Hi Jay,

We'll need "real developer" expertise on this, but my understanding of the
documentation is:

Client talks to Name node to get Node/Block assignments,  client then talks
to node 1: write, fwd, node 2: write, fwd, node 3: write, ack node 2, node
2: ack node1, node 1: ack Client and Name Node.

write includes data write and checksum, ack = report success.  The fwd
requests happen AFTER successful write and checksum.

Hope this helps.
Chris


On Tue, Dec 18, 2012 at 3:56 PM, Jay Vyas <jayunit100@gmail.com> wrote:

> Hi :
>
> Do data nodes, when they receive write requests, forward the request to
> the next datanode in the chain after appending to a file? Or rather, do the
> write and forward asynchronously and at the same time?
>
> --
> Jay Vyas
> http://jayunit100.blogspot.com
>

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Hi Jay,<div><br></div><div>We&#39;ll need &quot;real developer&quot; expert=
ise on this, but my understanding of the documentation is:=A0</div><div><br=
></div><div>Client talks to Name node to get Node/Block assignments, =A0cli=
ent then talks to node 1: write, fwd, node 2: write, fwd, node 3: write, ac=
k node 2, node 2: ack node1, node 1: ack Client and Name Node.</div>
<div><br></div><div>write includes data write and checksum, ack =3D report =
success. =A0The fwd requests happen AFTER successful write and checksum.</d=
iv><div><br></div><div>Hope this helps.</div><div>Chris<br><br><br><br><div=
 class=3D"gmail_quote">
On Tue, Dec 18, 2012 at 3:56 PM, Jay Vyas <span dir=3D"ltr">&lt;<a href=3D"=
mailto:jayunit100@gmail.com" target=3D"_blank">jayunit100@gmail.com</a>&gt;=
</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .=
8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir=3D"ltr"><div>Hi : <br><br></div>Do data nodes, when they receive w=
rite requests, forward the request to the next datanode in the chain  after=
 appending to a file? Or rather, do the write and forward asynchronously an=
d at the same time?<span class=3D"HOEnZb"><font color=3D"#888888"><br clear=
=3D"all">

<div><div><br>-- <br>Jay Vyas<br><a href=3D"http://jayunit100.blogspot.com"=
 target=3D"_blank">http://jayunit100.blogspot.com</a><br>
</div></div></font></span></div>
</blockquote></div><br></div>

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