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From Frank Austin Nothaft <fnoth...@berkeley.edu>
Subject Re: How to 'Pipe' Binary Data in Apache Spark
Date Wed, 21 Jan 2015 19:30:01 GMT
Hi Venkat/Nick,

The Spark RDD.pipe method pipes text data into a subprocess and then receives text data back
from that process. Once you have the binary data loaded into an RDD properly, to pipe binary
data to/from a subprocess (e.g., you want the data in the pipes to contain binary, not text),
you need to implement your own, modified version of RDD.pipe. The implementation of RDD.pipe
spawns a process per partition (IIRC), as well as threads for writing to and reading from
the process (as well as stderr for the process). When writing via RDD.pipe, Spark calls *.toString
on the object, and pushes that text representation down the pipe. There is an example of how
to pipe binary data from within a mapPartitions call using the Scala API in lines 107-177
of this file. This specific code contains some nastiness around the packaging of downstream
libraries that we rely on in that project, so I’m not sure if it is the cleanest way, but
it is a workable way.

Regards,

Frank Austin Nothaft
fnothaft@berkeley.edu
fnothaft@eecs.berkeley.edu
202-340-0466

On Jan 21, 2015, at 9:17 AM, Venkat, Ankam <Ankam.Venkat@centurylink.com> wrote:

> I am trying to solve similar problem.  I am using option # 2 as suggested by Nick. 
>  
> I have created an RDD with sc.binaryFiles for a list of .wav files.  But, I am not able
to pipe it to the external programs. 
>  
> For example:
> >>> sq = sc.binaryFiles("wavfiles")  ß All .wav files stored on “wavfiles”
directory on HDFS
> >>> sq.keys().collect() ß works fine.  Shows the list of file names.
> >>> sq.values().collect() ß works fine.  Shows the content of the files.
> >>> sq.values().pipe(lambda x: subprocess.call(['/usr/local/bin/sox', '-t' 'wav',
'-', '-n', 'stats'])).collect() ß Does not work.  Tried different options. 
> AttributeError: 'function' object has no attribute 'read'
>  
> Any suggestions?
>  
> Regards,
> Venkat Ankam
>  
> From: Nick Allen [mailto:nick@nickallen.org] 
> Sent: Friday, January 16, 2015 11:46 AM
> To: user@spark.apache.org
> Subject: Re: How to 'Pipe' Binary Data in Apache Spark
>  
> I just wanted to reiterate the solution for the benefit of the community.
>  
> The problem is not from my use of 'pipe', but that 'textFile' cannot be used to read
in binary data. (Doh) There are a couple options to move forward.
>  
> 1. Implement a custom 'InputFormat' that understands the binary input data. (Per Sean
Owen)
>  
> 2. Use 'SparkContext.binaryFiles' to read in the entire binary file as a single record.
This will impact performance as it prevents the use of more than one mapper on the file's
data.
>  
> In my specific case for #1 I can only find one project from RIPE-NCC (https://github.com/RIPE-NCC/hadoop-pcap)
that does this. Unfortunately, it appears to only support a limited set of network protocols.
>  
>  
> On Fri, Jan 16, 2015 at 10:40 AM, Nick Allen <nick@nickallen.org> wrote:
> Per your last comment, it appears I need something like this:
>  
> https://github.com/RIPE-NCC/hadoop-pcap
>  
> Thanks a ton.  That get me oriented in the right direction.  
>  
> On Fri, Jan 16, 2015 at 10:20 AM, Sean Owen <sowen@cloudera.com> wrote:
> Well it looks like you're reading some kind of binary file as text.
> That isn't going to work, in Spark or elsewhere, as binary data is not
> even necessarily the valid encoding of a string. There are no line
> breaks to delimit lines and thus elements of the RDD.
> 
> Your input has some record structure (or else it's not really useful
> to put it into an RDD). You can encode this as a SequenceFile and read
> it with objectFile.
> 
> You could also write a custom InputFormat that knows how to parse pcap
> records directly.
> 
> On Fri, Jan 16, 2015 at 3:09 PM, Nick Allen <nick@nickallen.org> wrote:
> > I have an RDD containing binary data. I would like to use 'RDD.pipe' to pipe
> > that binary data to an external program that will translate it to
> > string/text data. Unfortunately, it seems that Spark is mangling the binary
> > data before it gets passed to the external program.
> >
> > This code is representative of what I am trying to do. What am I doing
> > wrong? How can I pipe binary data in Spark?  Maybe it is getting corrupted
> > when I read it in initially with 'textFile'?
> >
> > bin = sc.textFile("binary-data.dat")
> > csv = bin.pipe ("/usr/bin/binary-to-csv.sh")
> > csv.saveAsTextFile("text-data.csv")
> >
> > Specifically, I am trying to use Spark to transform pcap (packet capture)
> > data to text/csv so that I can perform an analysis on it.
> >
> > Thanks!
> >
> > --
> > Nick Allen <nick@nickallen.org>
> 
> 
>  
> --
> Nick Allen <nick@nickallen.org>
> 
> 
>  
> --
> Nick Allen <nick@nickallen.org>
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