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From "Nick Dimiduk (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11562) CopyTable should provide an option to shuffle the mapper tasks
Date Tue, 22 Jul 2014 14:20:39 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14070302#comment-14070302
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Nick Dimiduk commented on HBASE-11562:
--------------------------------------

This sounds like a useful detail. Make it the default behavior? In practice, shouldn't a well
balanced table have fairly random region -> RegionServer distribution? You see logically
adjacent regions piling up on the same RS?

> CopyTable should provide an option to shuffle the mapper tasks
> --------------------------------------------------------------
>
>                 Key: HBASE-11562
>                 URL: https://issues.apache.org/jira/browse/HBASE-11562
>             Project: HBase
>          Issue Type: Bug
>          Components: mapreduce
>    Affects Versions: 0.99.0, 0.94.20, 0.98.4
>            Reporter: Jean-Marc Spaggiari
>            Assignee: Jean-Marc Spaggiari
>         Attachments: HBASE-11562-v0-trunk.patch, HBASE-11562-v1-trunk.patch
>
>
> When doing a copy table from a table with a lot of regions to a table to way less regions,
on a cluster with limited number of mappers, since map tasks are ordered by key, tasks will
first run for the few first regions and will hotspot a single region server on the destination
side.
> To avoid this, we should submit the map tasks in a random order.
> This JIRA is to add this option to CopyTable and TableInputFormat



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