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From "Zhixuan Zhu" <z...@calpont.com>
Subject RE: question about file input format
Date Thu, 18 Aug 2011 15:50:17 GMT

Thanks very much for the prompt reply! It makes perfect sense. I'll give
it a try.


-----Original Message-----
From: Harsh J [mailto:harsh@cloudera.com] 
Sent: Thursday, August 18, 2011 10:03 AM
To: common-dev@hadoop.apache.org
Subject: Re: question about file input format


In that case you may simply set the key/value with dummy or nulls and
return true just once (same unread/read logic applies as in the
example). Then, using the input file name (via map.input.file or the
inputsplit), pass it to your spawned process and have it do the work.
You'll just be omitting the reading under next().

On Thu, Aug 18, 2011 at 7:35 PM, Zhixuan Zhu <zzhu@calpont.com> wrote:
> Thanks so much for your help! I'll study the sample code and see what
> should do. My mapper will actually invoke another shell process to
> in the file and do its job. I just need to get the input file names
> pass it to the separate process from my mapper. That case I don't need
> to read the file to memory right? How should I implement the next
> function accordingly?
> Thanks again,
> Grace
> -----Original Message-----
> From: Harsh J [mailto:harsh@cloudera.com]
> Sent: Wednesday, August 17, 2011 9:36 PM
> To: common-dev@hadoop.apache.org
> Subject: Re: question about file input format
> Zhixuan,
> You'll require two things here, as you've deduced correctly:
> Under InputFormat
> - isSplitable -> False
> - getRecordReader -> A simple implementation that reads the whole
> file's bytes to an array/your-construct and passes it (as part of
> next(), etc.).
> For example, here's a simple record reader impl you can return
> (untested, but you'll get the idea of reading whole files, and porting
> to new API is easy as well): https://gist.github.com/1153161
> P.s. Since you are reading whole files into memory, keep an eye out
> for memory usage (the above example has a 10 MB limit per file, for
> example). You could run out of memory easily if you don't handle the
> cases properly.
> On Thu, Aug 18, 2011 at 4:28 AM, Zhixuan Zhu <zzhu@calpont.com> wrote:
>> I'm new Hadoop and currently using Hadoop 0.20.2 to try out some
> simple
>> tasks. I'm trying to send each whole file of the input directory to
> the
>> mapper without splitting them line by line. How should I set the
>> format class? I know I could derive a customized FileInputFormat
>> and override the isSplitable function. But I have no idea how to
>> implement around the record reader. Any suggestion or a sample code
> will
>> be greatly appreciated.
>> Thanks in advance,
>> Grace
> --
> Harsh J

Harsh J

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