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Hadoop, mail # user - Re: executing files on hdfs via hadoop not possible? is JNI/JNA a reasonable solution?


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Re: executing files on hdfs via hadoop not possible? is JNI/JNA a reasonable solution?
Julian Bui 2013-03-17, 20:35
Ah, thanks for clarifying, Harsh,

One thing that concerns me is that you wrote "input can be mere HDFS file
path strings" which implies that the tasks will not be guaranteed to run
with the data, is that correct?

-Julian

On Sun, Mar 17, 2013 at 6:28 AM, Harsh J <[EMAIL PROTECTED]> wrote:

> Hi,
>
> Yes, streaming lets you send in arbitrary programs and execute them
> upon the input and helps collect the output, such as a shell script or
> a python script (its agnostic to what you send as long as you also
> send full launching environment and command instructions). The same
> can be leveraged to have your MR environment start a number of map
> tasks whose input can be mere HDFS file path strings (but not the file
> data) and that your program leverages libhdfs (shipped along or
> installed on all nodes) to read those paths and process them in a way
> you see fit. Essentially, you can tweak the streaming functionalities
> to make it do what you need it/achieve different ways of
> parallelism/etc..
>
> Yes, what am suggesting is perhaps similar to Hadoop Pipes, but that's
> generally been out of major use in the past few major releases we've
> made and generally Streaming is recommended in its favor.
>
> On Sun, Mar 17, 2013 at 4:20 PM, Julian Bui <[EMAIL PROTECTED]> wrote:
> > Hello Harsh,
> >
> > Thanks for the reply.  I just want to verify that I understand your
> > comments.
> >
> > It sounds like you're saying I should write a c/c++ application and get
> > access to hdfs using libhdfs.  What I'm a little confused about is what
> you
> > mean by "use a streaming program".  Do you mean I should use the hadoop
> > streaming interface to call some native binary that I wrote?  I was not
> even
> > aware that the streaming interface could execute native binaries.  I
> thought
> > that anything using the hadoop streaming interface only interacts with
> stdin
> > and stdout and cannot make modifications to the hdfs.  Or did you mean
> that
> > I should use hadoop pipes to write a c/c++ application?
> >
> > Anyway, I hope that you can help me clear things up in my head.
> >
> > Thanks,
> > -Julian
> >
> > On Sun, Mar 17, 2013 at 2:50 AM, Harsh J <[EMAIL PROTECTED]> wrote:
> >>
> >> You're confusing two things here. HDFS is a data storage filesystem.
> >> MR does not have anything to do with HDFS (generally speaking).
> >>
> >> A reducer runs as a regular JVM on a provided node, and can execute
> >> any program you'd like it to by downloading it onto its configured
> >> local filesystem and executing it.
> >>
> >> If your goal is merely to run a regular program over data that is
> >> sitting in HDFS, that can be achieved. If your library is in C then
> >> simply use a streaming program to run it and use libhdfs' HDFS API
> >> (C/C++) to read data into your functions from HDFS files. Would this
> >> not suffice?
> >>
> >> On Sun, Mar 17, 2013 at 3:09 PM, Julian Bui <[EMAIL PROTECTED]>
> wrote:
> >> > Hi hadoop users,
> >> >
> >> > I just want to verify that there is no way to put a binary on HDFS and
> >> > execute it using the hadoop java api.  If not, I would appreciate
> advice
> >> > in
> >> > getting in creating an implementation that uses native libraries.
> >> >
> >> > "In contrast to the POSIX model, there are no sticky, setuid or setgid
> >> > bits
> >> > for files as there is no notion of executable files."  Is there no
> >> > workaround?
> >> >
> >> > A little bit more about what I'm trying to do.  I have a binary that
> >> > converts my image to another image format.  I currently want to put it
> >> > in
> >> > the distributed cache and tell the reducer to execute the binary on
> the
> >> > data
> >> > on hdfs.  However, since I can't set the execute permission bit on
> that
> >> > file, it seems that I cannot do that.
> >> >
> >> > Since I cannot use the binary, it seems like I have to use my own
> >> > implementation to do this.  The challenge is that these libraries
> that I
> >> > can
> >> > use to do this are .a and .so files.  Would I have to use JNI and