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https://issues.apache.org/jira/browse/HADOOP-13975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15859827#comment-15859827
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Erik Krogen commented on HADOOP-13975:
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This seems very useful! Thanks for working on this.
Why is there both {{parseThreadsPerMap}} and {{parseNumThreadsPerMap}} in
{{OptionsParser}}? It seems only one of them is used. Additionally the error
message is incorrect in both of them, with one referring to {{MAX_MAPS}} and
one referring to {{NUM_LISTSSTATUS_THREADS}}.
> Allow DistCp to use MultiThreadedMapper
> ---------------------------------------
>
> Key: HADOOP-13975
> URL: https://issues.apache.org/jira/browse/HADOOP-13975
> Project: Hadoop Common
> Issue Type: New Feature
> Components: tools/distcp
> Affects Versions: 3.0.0-alpha1
> Reporter: Zheng Shao
> Assignee: Zheng Shao
> Priority: Minor
> Attachments: HADOOP-distcp-multithreaded-mapper-branch26.1.patch,
> HADOOP-distcp-multithreaded-mapper-branch26.2.patch,
> HADOOP-distcp-multithreaded-mapper-branch26.3.patch,
> HADOOP-distcp-multithreaded-mapper-branch26.4.patch,
> HADOOP-distcp-multithreaded-mapper-trunk.1.patch,
> HADOOP-distcp-multithreaded-mapper-trunk.2.patch,
> HADOOP-distcp-multithreaded-mapper-trunk.3.patch,
> HADOOP-distcp-multithreaded-mapper-trunk.4.patch
>
>
> Although distcp allow users to control the parallelism via number of mappers,
> sometimes it's desirable to run fewer mappers but more threads per mapper.
> Since distcp is network bound (either by throughput or more frequently by
> latency of creating connections, opening files, reading/writing files, and
> closing files), this can make each mapper much more efficient.
> In that way, a lot of resources can be shared so we can save memory and
> connections to NameNode.
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