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From "Runping Qi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1440) JobClient should not sort input-splits
Date Thu, 31 May 2007 05:11:16 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12500287
] 

Runping Qi commented on HADOOP-1440:
------------------------------------


Milind,

What contract are you referring?
The current way of choosing output file names is purely incidental.
The output file names do not bear any meaning, except that they are all distinct.

I don't think we support the case where  a single split is constructed from multiple files.
If we do in the future, we can choose any one of them, as long as they are distinct.



> JobClient should not sort input-splits
> --------------------------------------
>
>                 Key: HADOOP-1440
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1440
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: mapred
>    Affects Versions: 0.12.3
>         Environment: All
>            Reporter: Milind Bhandarkar
>             Fix For: 0.14.0
>
>
> Currently, the JobClient sorts the InputSplits returned by InputFormat in descending
order, so that the map tasks corresponding to larger input-splits are scheduled first for
execution than smaller ones. However, this causes problems in applications that produce data-sets
partitioned similarly to the input partition with -reducer NONE.
> With -reducer NONE, map task i produces part-i. Howver, in the typical applications that
use -reducer NONE it should produce a partition that has the same index as the input parrtition.
> (Of course, this requires that each partition should be fed in its entirety to a map,
rather than splitting it into blocks, but that is a separate issue.)
> Thus, sorting input splits should be either controllable via a configuration variable,
or the FileInputFormat should sort the splits and JobClient should honor the order of splits.

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