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From: Alberto Cordioli <cordioli.alberto@gmail.com>
Date: Mon, 15 Oct 2012 21:11:27 +0200
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 <CAFnReZYL4EpxYOMJV6VgNAfMhBTyrvhgVmV18tO+aFCTBFbaMA@mail.gmail.com>
Subject: GroupingComparator
To: user@hadoop.apache.org
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Hi all,

a very strange thing is happening with my hadoop program.
My map simply emits tuples with a custom object as key (which
implement WritableComparable).
The object is made of 2 fields, and I implement my partitioner and
groupingclass in such a way that only the first field is taken into
account.
The second field is just a tag and could be 1 or 2.

This is the reducer's snippet:

tag = key.getSecondField();
Iterator it1 = values.iterator();
while(it1.hasNext()){
        it1.next();
        collector.emit(new Text("dummy"), tag);
}

I would expect in my output all the lines with:
dummy       1
...
dummy       1

but actually the value of tag changes in time and I obtain this type of output:

dummy    1
...
dummy    1
dummy    2
...
dummy    2


Someone could explain me way, please?


Thanks.


-- 
Alberto Cordioli