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https://issues.apache.org/jira/browse/HADOOP-1440?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12503614
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Doug Cutting commented on HADOOP-1440:
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bq. The problem from my point of view is just that right now the name of the
task controls the scheduling of the task. They should be independent of each
other.
Right. I agree. So I think we should, in the short term, to resolve this
issue:
1. Use the order returned from getSplits() to determine the map name, and hence
the output names when reduce is disabled.
2. Continue to sort by the length of the input to determine task execution
order.
Does that make sense?
> 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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