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From "Bob Cummins (JIRA)" <j...@apache.org>
Subject [jira] Created: (MAPREDUCE-2382) Key/Value ordering within a single key/value set when multiple values exist for a key
Date Mon, 14 Mar 2011 12:37:30 GMT
Key/Value ordering within a single key/value set when multiple values exist for a key
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                 Key: MAPREDUCE-2382
                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2382
             Project: Hadoop Map/Reduce
          Issue Type: Improvement
          Components: client
    Affects Versions: 0.20.2
            Reporter: Bob Cummins
            Priority: Minor


>>The context of this issue is entirely within one key/value(s) pair/set, NOT between
key/value sets as they are funneled to a reducer  by mappers.<<

When mapper writes multiple values for a key, the underlying collection class maps each of
the values to the key, but not always in chronological order. If chronological order were
guaranteed each of the values mapped to the key, each of the values could be understood as
specific and different parameters between the mapper and the reducer.

I've done little tricks like having the mapper flag one a the values by making it a  negative
number, which the reducer recognizes and can write it to hbase as a unique column value.This
is a kluge workaround which it would be nice to not have to do.

Used to formulate this suggestion:
TableMapper<ImmutableBytesWritable,IntWritable>
TableReducer<ImmutableBytesWritable,IntWritable, ImmutableBytesWritable>



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