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From "Owen O'Malley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1440) JobClient should not sort input-splits
Date Fri, 01 Jun 2007 16:35:15 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12500755
] 

Owen O'Malley commented on HADOOP-1440:
---------------------------------------

map.input.file is not always defined. In particular, it is only defined if the InputSplit
happens to be a FileSplit. It was defined as a convenience for Mappers before we provided
them access to the InputSplit directly. Certainly no part of the framework should assume it
will be defined.

> 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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