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https://issues.apache.org/jira/browse/HADOOP-2399?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Owen O'Malley updated HADOOP-2399:
----------------------------------
Release Note: The key and value objects that are given to the Combiner and
Reducer are now reused between calls. This is much more efficient, but the user
can not assume the objects are constant.
Hadoop Flags: [Incompatible change, Reviewed]
> Input key and value to combiner and reducer should be reused
> ------------------------------------------------------------
>
> Key: HADOOP-2399
> URL: https://issues.apache.org/jira/browse/HADOOP-2399
> Project: Hadoop Core
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.15.1
> Reporter: Owen O'Malley
> Assignee: Owen O'Malley
> Fix For: 0.17.0
>
> Attachments: 2399-3.patch, 2399-4.patch
>
>
> Currently, the input key and value are recreated on every iteration for input
> to the combiner and reducer. It would speed up the system substantially if we
> reused the keys and values. The down side of doing it, is that it may break
> applications that count on holding references to previous keys and values,
> but I think it is worth doing.
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