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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1440) JobClient should not sort input-splits
Date Mon, 11 Jun 2007 21:31:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12503635
] 

Doug Cutting commented on HADOOP-1440:
--------------------------------------

bq. That does not really address the problem this Jira tries to address:

I think it does.  Whether the input files are splittable is up to the input format.  If reduce
is disabled, then I proposed (above) that the order of the input splits should determine the
numbering of output files.  So what's not addressed?

Changing the kernel to base the output file names directly on the input file names would break
a number of abstraction boundaries.  But I don't see how this is required.  The list of input
files and output files should correspond one-to-one.

> 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
>            Assignee: 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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