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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-2382) Key/Value ordering within a single key/value set when multiple values exist for a key
Date Mon, 14 Mar 2011 17:04:36 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2382?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13006516#comment-13006516
] 

Todd Lipcon commented on MAPREDUCE-2382:
----------------------------------------

Bob, it seems like this is a feature request for a new API for HBase, and probably doesn't
belong on the MR JIRA. Am I misunderstanding?

> Key/Value ordering within a single key/value set when multiple values exist for a key
> -------------------------------------------------------------------------------------
>
>                 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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