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From JoshRosen <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-2205] [SQL] Avoid unnecessary exchange ...
Date Sat, 01 Aug 2015 19:43:31 GMT
Github user JoshRosen commented on a diff in the pull request:

    https://github.com/apache/spark/pull/7773#discussion_r36036422
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/physical/partitioning.scala
---
    @@ -86,8 +87,12 @@ sealed trait Partitioning {
        */
       def satisfies(required: Distribution): Boolean
     
    -  /** Returns the expressions that are used to key the partitioning. */
    -  def keyExpressions: Seq[Expression]
    +  /**
    +   * Returns true iff we can say that the partitioning scheme of this [[Partitioning]]
    +   * guarantees the same partitioning scheme described by `other`.
    +   */
    +  // TODO: Add an example once we have the `nullSafe` concept.
    +  def guarantees(other: Partitioning): Boolean
    --- End diff --
    
    I think that we should only consider a name like `semanticEqual` or `semanticEquiv` if
`a.guarantees(b)` implies `b.guarantees(a)` and vice-versa.


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