[jira] [Created] (SPARK-11135) Exchange sort-planning logic may incorrect avoid sorts

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

Josh Rosen created SPARK-11135:
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             Summary: Exchange sort-planning logic may incorrect avoid sorts
                 Key: SPARK-11135
                 URL: https://issues.apache.org/jira/browse/SPARK-11135
             Project: Spark
          Issue Type: Bug
          Components: SQL
            Reporter: Josh Rosen
            Assignee: Josh Rosen
            Priority: Blocker


In Spark SQL, the Exchange planner tries to avoid unnecessary sorts in cases where the data has already been sorted by a superset of the requested sorting columns. For instance, let's say that a query calls for an operator's input to be sorted by `a.asc` and the input happens to already be sorted by `[a.asc, b.asc]`. In this case, we do not need to re-sort the input. The converse, however, is not true: if the query calls for `[a.asc, b.asc]`, then `a.asc` alone will not satisfy the ordering requirements, requiring an additional sort to be planned by Exchange.

However, the current Exchange code gets this wrong and incorrectly skips sorting when the existing output ordering is a subset of the required ordering. This is simple to fix, however.



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