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[SPARK-43095][SQL] Avoid Once strategy's idempotence is broken for batch: Infer Filters #40742

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[SPARK-43095][SQL] Avoid Once strategy's idempotence is broken for batch: Infer Filters #40742

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Avoid Once strategy's idempotence is broken for batch: Infer Filters
wangyum Apr 11, 2023
0181764
Address comments
wangyum Apr 13, 2023
842faec
fix
wangyum Apr 13, 2023
f1ae941
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wangyum Apr 14, 2023
917fa3e
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wangyum Apr 14, 2023
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8 changes: 5 additions & 3 deletions ...yst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/QueryPlanConstraints.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -66,13 +66,15 @@ trait ConstraintHelper {
val predicates = constraints.filterNot(_.isInstanceOf[IsNotNull])
predicates.foreach {
case eq @ EqualTo(l: Attribute, r: Attribute) =>
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not related to this PR, but shall we match Equality here?

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Yes. It seems ok.

val candidateConstraints = predicates - eq
// Also remove EqualNullSafe with the same l and r to avoid Once strategy's idempotence
// is broken. l = r and l <=> r can infer l <=> l and r <=> r which is useless.
val candidateConstraints = predicates - eq - EqualNullSafe(l, r)
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if l.semanticEquals(r), we don't need to infer predicates at all, right?

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@wangyum wangyum Apr 13, 2023 •
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Yes. But the current situation is like this: l <=> l and r <=> r is inferred from l === r and l <=> r. At this time, l.semanticEquals(r) is false.

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ah got it. Let's add a code comment to explain it with this example.

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@cloud-fan cloud-fan Apr 13, 2023 •
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can you explain it a bit more about why it makes the optimizer not idempotent?

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For example:

Join Inner, (a#0 = a#7)
:- Project [a#0, a#0 AS xa#3]
:  +- Join Inner, (a#0 = a#4)
:     :- LocalRelation <empty>, [a#0, b#1, c#2]
:     +- LocalRelation <empty>, [a#4, b#5, c#6]
+- LocalRelation <empty>, [a#7, b#8, c#9]

After InferFiltersFromConstraints:

Join Inner, (a#0 = a#7)
:- Filter ((a#0 <=> a#0) AND (xa#3 <=> xa#3))
:  +- Project [a#0, a#0 AS xa#3]
:     +- Join Inner, (a#0 = a#4)
:        :- Filter isnotnull(a#0)
:        :  +- LocalRelation <empty>, [a#0, b#1, c#2]
:        +- Filter isnotnull(a#4)
:           +- LocalRelation <empty>, [a#4, b#5, c#6]
+- Filter isnotnull(a#7)
   +- LocalRelation <empty>, [a#7, b#8, c#9]

And run InferFiltersFromConstraints again. The left side constraints:

(a#0 <=> xa#3)
(xa#3 = a#0)
(a#0 <=> a#0)
(xa#3 <=> xa#3)

The right side constraints:

(isnotnull(a#7))

Join condition is:

(a#0 = a#7)

Based on these constraints, the inferred result is:

(a#7 <=> xa#3)
(xa#3 = a#7)
(a#7 <=> a#7)

(a#7 <=> a#7) is a valid constraints for right side. The result:

Join Inner, (a#0 = a#7)
:- Filter ((a#0 <=> a#0) AND (xa#3 <=> xa#3))
:  +- Project [a#0, a#0 AS xa#3]
:     +- Join Inner, (a#0 = a#4)
:        :- Filter isnotnull(a#0)
:        :  +- LocalRelation <empty>, [a#0, b#1, c#2]
:        +- Filter isnotnull(a#4)
:           +- LocalRelation <empty>, [a#4, b#5, c#6]
+- Filter (a#7 <=> a#7)
   +- Filter isnotnull(a#7)
      +- LocalRelation <empty>, [a#7, b#8, c#9]

inferredConstraints ++= replaceConstraints(candidateConstraints, l, r)
inferredConstraints ++= replaceConstraints(candidateConstraints, r, l)
case eq @ EqualTo(l @ Cast(_: Attribute, _, _, _), r: Attribute) =>
inferredConstraints ++= replaceConstraints(predicates - eq, r, l)
inferredConstraints ++= replaceConstraints(predicates - eq - EqualNullSafe(l, r), r, l)
case eq @ EqualTo(l: Attribute, r @ Cast(_: Attribute, _, _, _)) =>
inferredConstraints ++= replaceConstraints(predicates - eq, l, r)
inferredConstraints ++= replaceConstraints(predicates - eq - EqualNullSafe(l, r), l, r)
case _ => // No inference
}
inferredConstraints -- constraints
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28 changes: 28 additions & 0 deletions ...test/scala/org/apache/spark/sql/catalyst/optimizer/InferFiltersFromConstraintsSuite.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -371,4 +371,32 @@ class InferFiltersFromConstraintsSuite extends PlanTest {
val optimized = Optimize.execute(originalQuery)
comparePlans(optimized, correctAnswer)
}

test("SPARK-43095: Avoid Once strategy's idempotence is broken for batch: Infer Filters") {
val x = testRelation.as("x")
val y = testRelation.as("y")
val z = testRelation.as("z")

// Removes EqualNullSafe when constructing candidate constraints
comparePlans(
InferFiltersFromConstraints(x.select($"x.a", $"x.a".as("xa"))
.where($"xa" <=> $"x.a" && $"xa" === $"x.a").analyze),
x.select($"x.a", $"x.a".as("xa"))
.where($"xa".isNotNull && $"x.a".isNotNull && $"xa" <=> $"x.a" && $"xa" === $"x.a").analyze)

// Once strategy's idempotence is not broken
val originalQuery =
x.join(y, condition = Some($"x.a" === $"y.a"))
.select($"x.a", $"x.a".as("xa")).as("xy")
.join(z, condition = Some($"xy.a" === $"z.a")).analyze

val correctAnswer =
x.where($"a".isNotNull).join(y.where($"a".isNotNull), condition = Some($"x.a" === $"y.a"))
.select($"x.a", $"x.a".as("xa")).as("xy")
.join(z.where($"a".isNotNull), condition = Some($"xy.a" === $"z.a")).analyze

val optimizedQuery = InferFiltersFromConstraints(originalQuery)
comparePlans(optimizedQuery, correctAnswer)
comparePlans(InferFiltersFromConstraints(optimizedQuery), correctAnswer)
}
}