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From "Jonathan Chang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HIVE-1404) Allow UDAFs to turn off map-side aggregation
Date Mon, 14 Jun 2010 20:33:13 GMT
Allow UDAFs to turn off map-side aggregation
--------------------------------------------

                 Key: HIVE-1404
                 URL: https://issues.apache.org/jira/browse/HIVE-1404
             Project: Hadoop Hive
          Issue Type: New Feature
            Reporter: Jonathan Chang
            Priority: Minor


Some UDAFs such as COLLECT will not work with map-side aggregation (because each mapper must
hold all of its contents in memory).   To use such a function at the moment, one has to remember
to set hive.map.aggr.  This has two problems:

1.) The user has to remember to set this flag or else bad things will happen.
2.) The flag applies to the entire query plan rather than just the block containing the COLLECT
statement.

It would be good to have a bit in the UDAF which would tell the compiler to turn off map-side
aggregation for just the block containing the UDAF.

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