Allow UDAFs to turn off map-side aggregation
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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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