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From "Ning Zhang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HIVE-900) Map-side join failed if there are large number of mappers
Date Sat, 24 Oct 2009 00:43:59 GMT
Map-side join failed if there are large number of mappers
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                 Key: HIVE-900
                 URL: https://issues.apache.org/jira/browse/HIVE-900
             Project: Hadoop Hive
          Issue Type: Improvement
            Reporter: Ning Zhang
            Assignee: Ning Zhang


Map-side join is efficient when joining a huge table with a small table so that the mapper
can read the small table into main memory and do join on each mapper. However, if there are
too many mappers generated for the map join, a large number of mappers will simultaneously
send request to read the same block of the small table. Currently Hadoop has a upper limit
of the # of request of a the same block (250?). If that is reached a BlockMissingException
will be thrown. That cause a lot of mappers been killed. Retry won't solve but worsen the
problem.

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