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From Harsh J <ha...@cloudera.com>
Subject Re: executing files on hdfs via hadoop not possible? is JNI/JNA a reasonable solution?
Date Sun, 17 Mar 2013 13:28:04 GMT

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

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 <julianbui@gmail.com> 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 <harsh@cloudera.com> 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 <julianbui@gmail.com> 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
>> > package
>> > the libraries in the distributed cache and then have the reducer find
>> > and
>> > use those libraries on the task nodes?  Actually, I wouldn't want to use
>> > JNI, I'd probably want to use java native access (JNA) to do this.  Has
>> > anyone used JNA with hadoop and been successful?  Are there problems
>> > I'll
>> > encounter?
>> >
>> > Please let me know.
>> >
>> > Thanks,
>> > -Julian
>> --
>> Harsh J

Harsh J

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