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From "Ning Zhang (JIRA)" <j...@apache.org>
Subject [jira] Created: (HIVE-948) more query plan optimization rules
Date Mon, 23 Nov 2009 20:35:41 GMT
more query plan optimization rules 
-----------------------------------

                 Key: HIVE-948
                 URL: https://issues.apache.org/jira/browse/HIVE-948
             Project: Hadoop Hive
          Issue Type: Improvement
            Reporter: Ning Zhang


Many query plans are not optimal in that they contain redundant operators. Some examples are
unnecessary select operators (select followed by select, select output being the same as input
etc.). Even though these operators are not very expensive, they could account for around 10%
of CPU time in some simple queries. It seems they are low-hanging fruits that we should pick
first. 

BTW, it seems these optimization rules should be added at the last stage of the physical optimization
phase since some redundant operators are added to facilitate physical plan generation. 

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