more query plan optimization rules
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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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