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[SPARK-29213][SQL] Generate extra IsNotNull predicate in FilterExec #25902

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[SPARK-29213][SQL] Generate extra IsNotNull predicate in FilterExec #25902

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ad6df5c
[SPARK-29213] Make it consistent when get notnull output and generate…
wangshuo128 Sep 23, 2019
270172b
remove exprId both in notNullPreds and otherPreds when get notNullAtt…
wangshuo128 Sep 24, 2019
9ad9723
modify test table names
wangshuo128 Sep 24, 2019
c03dd95
Some slight modifications so we no longer depend on Hive.
wangshuo128 Sep 25, 2019
30e2ac7
Generate extra IsNotNull predicate for null check
wangshuo128 Sep 25, 2019
8480de2
Address some comments
wangshuo128 Sep 26, 2019
a8cb828
Code sytle modification
wangshuo128 Sep 26, 2019
124ad87
Refine test
wangshuo128 Sep 26, 2019
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remove exprId both in notNullPreds and otherPreds when get notNullAtt… 
…ributes
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wangshuo128 committed Sep 27, 2019
commit 270172bb23688ff823bb7f93e3f26ca357f52568
3 changes: 2 additions & 1 deletion sql/core/src/main/scala/org/apache/spark/sql/execution/basicPhysicalOperators.scala
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Expand Up @@ -110,14 +110,15 @@ case class FilterExec(condition: Expression, child: SparkPlan)

// The columns that will filtered out by `IsNotNull` could be considered as not nullable.
private val notNullAttributes = notNullPreds.flatMap(_.references).distinct.map(_.exprId)
.diff(otherPreds.flatMap(_.references).distinct.map(_.exprId))
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@cloud-fan cloud-fan Sep 24, 2019

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This fix seems sub-optimal to me. If we have a IsNotNull(a), then a should be a notNullAttribute even if a appears in otherPreds like EqualTo(a, b).

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@cloud-fan cloud-fan Sep 24, 2019

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I think the bug is about how we codegen null checks, the current logic is:

  1. split the predicates into notNullPreds (IsNotNull expressions) and otherPreds
  2. try codegen otherPreds first, then notNullPreds.
  3. if an other-predicate can leverage a specific not-null-predicate, then codegen that not-null-predicate first, so that we can codegen the other-predicate with non-nullable attributes.

There is a problem in step 3. Image that we have a IsNotNull(SubString(a)) and a SomeFunc(a). Then a is a not-null attribute for sure, even if there is no IsNullNull(a) predicate.

When we codegen SomeFunc(a), we can't find a IsNotNull(a) expression, so we skip the null check. However, we assume a is not nullable when codegen SomeFunc(a), which is wrong as IsNotNull(SubString(a)) has not been codegened yet.


// Mark this as empty. We'll evaluate the input during doConsume(). We don't want to evaluate
// all the variables at the beginning to take advantage of short circuiting.
override def usedInputs: AttributeSet = AttributeSet.empty

override def output: Seq[Attribute] = {
child.output.map { a =>
if (a.nullable && notNullPreds.exists(_.semanticEquals(a))) {
if (a.nullable && notNullAttributes.contains(a.exprId)) {
a.withNullability(false)
} else {
a
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