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[SPARK-23973][SQL] Remove consecutive Sorts #21072

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[SPARK-23973][SQL] Remove consecutive Sorts #21072

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[SPARK-23973][SQL] Remove consecutive Sorts
mgaido91 Apr 14, 2018
ff7d412
remove Sort operator separated by 0...n Project/Filter operators
mgaido91 Apr 16, 2018
ac03bed
fix test
mgaido91 Apr 16, 2018
1d6ca1e
add test cases + fix typo
mgaido91 Apr 17, 2018
e7391f3
address comments
mgaido91 Apr 23, 2018
e2f4d4d
address comment
mgaido91 Apr 23, 2018
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5 changes: 4 additions & 1 deletion sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
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Expand Up @@ -736,12 +736,15 @@ object EliminateSorts extends Rule[LogicalPlan] {
}

/**
* Removes Sort operation if the child is already sorted
* Removes redundant Sort operation. This can happen:
* 1) if the child is already sorted
* 2) if the next operator is a Sort itself
*/
object RemoveRedundantSorts extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
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nit: now it's more efficient to do transformDown

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isn't it the same?

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@cloud-fan cloud-fan Apr 23, 2018 •
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assume the plan is

Sort
  Filter
    Sort
      Filter
        Sort
          OtherPlan

If we do transformUp, we hit the rule 3 times, which has some unnecessary transformation(OtherPlan is transformed 3 times). If it's transformDown, it's one-shot.

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yes, but I saw that transfrom actually does transformDown. Anyway, I see that this might change and here we best have transformDown

case Sort(orders, true, child) if SortOrder.orderingSatisfies(child.outputOrdering, orders) =>
child
case s @ Sort(_, _, Sort(_, _, child)) => s.copy(child = child)
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Thanks for doing this! It might be useful to generalise this to any pair of sorts separated by 0 or more projections or filters. I did this for my SPARK-23975 PR, see: henryr@bb992c2#diff-a636a87d8843eeccca90140be91d4fafR322

What do you think?

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yes, it makes sense. I will do, thanks.

}
}

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7 changes: 7 additions & 0 deletions ...st/src/test/scala/org/apache/spark/sql/catalyst/optimizer/RemoveRedundantSortsSuite.scala
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Expand Up @@ -98,4 +98,11 @@ class RemoveRedundantSortsSuite extends PlanTest {
val correctAnswer = groupedAndResorted.analyze
comparePlans(optimized, correctAnswer)
}

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Could you add a test which explicitly confirms that sort.limit.sort is not simplified? I know the above two tests cover that case, but it's good to have one dedicated to testing this important property.

test("remove two consecutive sorts") {
val orderedTwice = testRelation.orderBy('a.asc).orderBy('b.desc)
val optimized = Optimize.execute(orderedTwice.analyze)
val correctAnswer = testRelation.orderBy('b.desc).analyze
comparePlans(optimized, correctAnswer)
}
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Can you add a test for three consecutive sorts? Two is the base case, three will help us show the inductive case :)

}