Rui Li created HIVE-7659:
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Summary: Unnecessary sort in query plan
Key: HIVE-7659
URL: https://issues.apache.org/jira/browse/HIVE-7659
Project: Hive
Issue Type: Improvement
Components: Spark
Reporter: Rui Li
For hive on spark.
Currently we rely on the sort order in RS to decide whether we need a sortByKey
transformation. However a simple group by query will also have the sort order
set to '+'.
Consider the query: select key from table group by key. The RS in the map work
will have sort order set to '+', thus requiring a sortByKey shuffle.
To avoid the unnecessary sort, we should either use another way to decide if
there has to be a sort shuffle, or we should set the sort order only when sort
is really needed.
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