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https://issues.apache.org/jira/browse/MAPREDUCE-801?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12736295#action_12736295
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Doug Cutting commented on MAPREDUCE-801:
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In PIG-878 Arun made a sensible suggestion, that the number of locations of a
split should not be greater than the replication level of the file. This could
be checked by FileInputFormat.
Another approach might be to add counters for rack-local and local task
placements and i/o. If the tasks are placed locally but the i/o is not done
locally, that's a bad sign.
> MAPREDUCE framework should issue warning with too many locations for a split
> ----------------------------------------------------------------------------
>
> Key: MAPREDUCE-801
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-801
> Project: Hadoop Map/Reduce
> Issue Type: New Feature
> Reporter: Hong Tang
>
> Customized input-format may be buggy and report misleading locations through
> input-split, an example of which is PIG-878. When an input split returns too
> many locations, it would not only artificially inflate the percentage of data
> local or rack local maps, but also force scheduler to use more memory and
> work harder to conduct task assignment.
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