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From: Dhaivat Pandya <dhaivatpandya@gmail.com>
Date: Sun, 22 Dec 2013 22:38:36 -0600
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Subject: Re: Datanode registration, port number
To: common-dev@hadoop.apache.org
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I understand that that is how the port is *later* retrieved, but how does
the namenode know the port in the first place? i.e. if the datanode sends a
packet to the namenode, how does the namenode know what port # the datanode
server is running on?


On Sun, Dec 22, 2013 at 10:28 PM, Shekhar Sharma <shekhar2581@gmail.com>wrote:

> Check the version file
> During the startup Datanode sends out a heart beat signal and NN
> assigns a storageID for it which is unique for every datanode.
> Using the storage id it identify the ip and port of a datanode
> Regards,
> Som Shekhar Sharma
> +91-8197243810
>
>
> On Mon, Dec 23, 2013 at 9:41 AM, Dhaivat Pandya <dhaivatpandya@gmail.com>
> wrote:
> > Hi,
> >
> > I'm currently trying to build a cache layer that should sit "on top" of
> the
> > datanode. Essentially, the namenode should know the port number of the
> > cache layer instead of that of the datanode (since the namenode then
> relays
> > this information to the default HDFS client). All of the communication
> > between the datanode and the namenode currently flows through my cache
> > layer (including heartbeats, etc.)
> >
> > *First question*: is there a way to tell the namenode where a datanode
> > should be? Any way to trick it into thinking that the datanode is on a
> port
> > number where it actually isn't? As far as I can tell, the port number is
> > obtained from the DatanodeId object; can this be set in the configuration
> > so that the port number derived is that of the cache layer?
> >
> > I spent quite a bit of time on the above question and I could not find
> any
> > sort of configuration option that would let me do that. So, I delved into
> > the HDFS source code and tracked down the DatanodeRegistration class.
> > However, I can't seem to find out *how* the NameNode figures out the
> > Datanode's port number or if I could somehow change the packets to
> reflect
> > the port number of cache layer? *Second question: *how does the namenode
> > figure out a newly-registered Datanode's port number?
> >
> > Thank you,
> >
> > Dhaivat
>

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