Cheng Hao created SPARK-4234:
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Summary: Always do paritial aggregation
Key: SPARK-4234
URL: https://issues.apache.org/jira/browse/SPARK-4234
Project: Spark
Issue Type: Improvement
Components: SQL
Reporter: Cheng Hao
Currently, UDAF developer optionally implement a partial aggregation function,
However this probably cause performance issue by allowing do that. We actually
can always force developers to provide the partial aggregation function as Hive
does, hence we will always get the `mapside` aggregation optimization.
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