[jira] [Created] (SPARK-8317) Do not push sort into shuffle in Exchange operator

["Josh Rosen (JIRA)" <ji...@apache.org>]

Josh Rosen created SPARK-8317:
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             Summary: Do not push sort into shuffle in Exchange operator
                 Key: SPARK-8317
                 URL: https://issues.apache.org/jira/browse/SPARK-8317
             Project: Spark
          Issue Type: Improvement
          Components: SQL
            Reporter: Josh Rosen
            Assignee: Josh Rosen


In some cases, Spark SQL pushes sorting operations into the shuffle layer by specifying a key ordering as part of the shuffle dependency. I think that we should not do this:

- Since we do not delegate aggregation to Spark's shuffle, specifying the keyOrdering as part of the shuffle has no effect on the shuffle map side.
- By performing the shuffle ourselves (by inserting a sort operator after the shuffle instead), we can use the Exchange planner to choose specialized sorting implementations based on the types of rows being sorted.
- We can remove some complexity from SqlSerializer2 by not requiring it to know about sort orderings, since SQL's own sort operators will already perform the necessary defensive copying.



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