[GitHub] spark pull request #17708: [SPARK-20413] Add new query hint NO_COLLAPSE.

[hvanhovell <gi...@git.apache.org>]

Github user hvanhovell commented on a diff in the pull request:

    https://github.com/apache/spark/pull/17708#discussion_r112511878
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/basicLogicalOperators.scala ---
    @@ -387,6 +387,13 @@ case class BroadcastHint(child: LogicalPlan) extends UnaryNode {
     }
     
     /**
    + * A hint for the optimizer that we should not merge two projections.
    + */
    +case class NoCollapseHint(child: LogicalPlan) extends UnaryNode {
    --- End diff --
    
    The problem with this approach is that most other optimizations won't work with this, for example predicate push down.


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