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Posted to common-user@hadoop.apache.org by Alex Loddengaard <al...@cloudera.com> on 2009/04/10 19:43:18 UTC

Re: Does the HDFS client read the data from NameNode, or from DataNode directly?

Data is streamed directly from the data nodes themselves.  The name node is
only queried for block locations and other meta data.

Alex

On Fri, Apr 10, 2009 at 8:33 AM, Stas Oskin <st...@gmail.com> wrote:

> Hi.
>
> I wanted to verify a point about HDFS client operations:
>
> When asking for file, is the all communication done through the NameNode?
> Or
> after being pointed to correct DataNode, does the HDFS works directly
> against it?
>
> Also, NameNode provides a URL named "streamFile" which allows any HTTP
> client to get the stored files. Any idea how it's operations compare in
> terms of speed to client HDFS access?
>
> Regards.
>

Re: Does the HDFS client read the data from NameNode, or from DataNode directly?

Posted by Stas Oskin <st...@gmail.com>.

Thanks, this is what I thought.
Regards.

2009/4/10 Alex Loddengaard <al...@cloudera.com>

> Data is streamed directly from the data nodes themselves.  The name node is
> only queried for block locations and other meta data.
>
> Alex
>
> On Fri, Apr 10, 2009 at 8:33 AM, Stas Oskin <st...@gmail.com> wrote:
>
> > Hi.
> >
> > I wanted to verify a point about HDFS client operations:
> >
> > When asking for file, is the all communication done through the NameNode?
> > Or
> > after being pointed to correct DataNode, does the HDFS works directly
> > against it?
> >
> > Also, NameNode provides a URL named "streamFile" which allows any HTTP
> > client to get the stored files. Any idea how it's operations compare in
> > terms of speed to client HDFS access?
> >
> > Regards.
> >
>