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MapReduce, mail # user - RE: hadoop 1.0.3 equivalent of MultipleTextOutputFormat


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RE: hadoop 1.0.3 equivalent of MultipleTextOutputFormat
Tony Burton 2012-08-29, 16:00
Success so far!

I followed the example given by Tom on the link to the MultipleOutputs.html API you suggested.

I implemented a WordCount MR job using hadoop 1.0.3 and segmented the output depending on word length: output to directory "sml" for less than 10 characters, "med" for between 10 and 20 characters, "lrg" otherwise.

I used out.write(key, new IntWritable(sum), generateFilename(key, sum)); to write the output, and generateFileName to create the custom directory name/filename. You need to provide the start of the filename as well otherwise your output files will be -r-00000, -r-00001 etc. (so, for example, return "sml/part"; etc)

Also required: as Tom states, override Reducer.setup() to create the MultipleOutputs. However, Tom's puzzle left for the reader is that you also need to override Reducer.cleanup() and call close() on your MultipleOutputs object. Forget to do this and your segmented files will be empty.

One observation: although it's not the end of the world, as well as my segmented output I also get a zero-size part-r-00000 file in the base of my output path. Is there any way to prevent creation of this file?

Thanks again Harsh for pointing the way.

Tony

-----Original Message-----
From: Tony Burton [mailto:[EMAIL PROTECTED]]
Sent: 29 August 2012 11:38
To: [EMAIL PROTECTED]
Subject: RE: hadoop 1.0.3 equivalent of MultipleTextOutputFormat

Thanks Harsh! Will try it out and report back later.
-----Original Message-----
From: Harsh J [mailto:[EMAIL PROTECTED]]
Sent: 29 August 2012 11:12
To: [EMAIL PROTECTED]
Subject: Re: hadoop 1.0.3 equivalent of MultipleTextOutputFormat

Hi Tony,

Seeing your new question, I recalled Tom's post to a user once, here:
https://groups.google.com/a/cloudera.org/d/msg/cdh-user/pdyVyydt5Ys/1CaLukt4v1AJ

This specific call allows you to specify / characters in your name,
that gets translated into creation of directories automatically:
http://hadoop.apache.org/common/docs/stable/api/org/apache/hadoop/mapreduce/lib/output/MultipleOutputs.html#write(KEYOUT,%20VALUEOUT,%20java.lang.String)
(The last argument is where you will need to specify the path)

Try it out and let us know!

On Tue, Aug 28, 2012 at 7:06 PM, Tony Burton <[EMAIL PROTECTED]> wrote:
> Hi Harsh
>
> Thanks for the reply - my understanding is that with MultipleOutputs I can write differently named files into the same target directory. With MultipleTextOutputFormat I was able to override the target directory name to perform the segmentation, by overriding generateFileNameForKeyValue().
>
> Does the 1.0.3 MultipleOutputs give me the ability to alter the target directory name as well as the file name?
>
> Thanks,
>
> Tony
>
>
>
> -----Original Message-----
> From: Harsh J [mailto:[EMAIL PROTECTED]]
> Sent: 28 August 2012 13:44
> To: [EMAIL PROTECTED]
> Subject: Re: hadoop 1.0.3 equivalent of MultipleTextOutputFormat
>
> The Multiple*OutputFormat have been deprecated in favor of the generic
> MultipleOutputs API. Would using that instead work for you?
>
> On Tue, Aug 28, 2012 at 6:05 PM, Tony Burton <[EMAIL PROTECTED]> wrote:
>> Hi,
>>
>> I've seen that org.apache.hadoop.mapred.lib.MultipleTextOutputFormat is good for writing results into (for example) different directories created on the fly. However, now I'm implementing a MapReduce job using Hadoop 1.0.3, I see that the new API no longer supports MultipleTextOutputFormat. Is there an equivalent that I can use, or will it be supported in a future release?
>>
>> Thanks,
>>
>> Tony
>>
>>
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