Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/19912#discussion_r155411680
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -64,50 +64,91 @@ object ConstantFolding extends Rule[LogicalPlan] {
* }}}
*
* Approach used:
- * - Start from AND operator as the root
- * - Get all the children conjunctive predicates which are EqualTo /
EqualNullSafe such that they
- * don't have a `NOT` or `OR` operator in them
* - Populate a mapping of attribute => constant value by looking at all
the equals predicates
* - Using this mapping, replace occurrence of the attributes with the
corresponding constant values
* in the AND node.
*/
object ConstantPropagation extends Rule[LogicalPlan] with PredicateHelper {
- private def containsNonConjunctionPredicates(expression: Expression):
Boolean = expression.find {
- case _: Not | _: Or => true
- case _ => false
- }.isDefined
-
def apply(plan: LogicalPlan): LogicalPlan = plan transform {
- case f: Filter => f transformExpressionsUp {
- case and: And =>
- val conjunctivePredicates =
- splitConjunctivePredicates(and)
- .filter(expr => expr.isInstanceOf[EqualTo] ||
expr.isInstanceOf[EqualNullSafe])
- .filterNot(expr => containsNonConjunctionPredicates(expr))
-
- val equalityPredicates = conjunctivePredicates.collect {
- case e @ EqualTo(left: AttributeReference, right: Literal) =>
((left, right), e)
- case e @ EqualTo(left: Literal, right: AttributeReference) =>
((right, left), e)
- case e @ EqualNullSafe(left: AttributeReference, right: Literal)
=> ((left, right), e)
- case e @ EqualNullSafe(left: Literal, right: AttributeReference)
=> ((right, left), e)
- }
-
- val constantsMap = AttributeMap(equalityPredicates.map(_._1))
- val predicates = equalityPredicates.map(_._2).toSet
+ case f: Filter =>
+ val (newCondition, _) = traverse(f.condition, replaceChildren = true)
+ if (newCondition.isDefined) {
+ f.copy(condition = newCondition.get)
+ } else {
+ f
+ }
+ }
- def replaceConstants(expression: Expression) = expression
transform {
- case a: AttributeReference =>
- constantsMap.get(a) match {
- case Some(literal) => literal
- case None => a
- }
+ /**
+ * Traverse a condition as a tree and replace attributes with constant
values.
+ * - If the child of [[And]] is [[EqualTo]] or [[EqualNullSafe]],
propagate the mapping
+ * of attribute => constant.
+ * - If the current [[And]] node is not child of another [[And]],
replace occurrence of the
+ * attributes with the corresponding constant values in both children
with propagated mapping.
+ * @param condition condition to be traversed
+ * @param replaceChildren whether to replace attributes with the
corresponding constant values
+ */
--- End diff --
Add doc to explain return value?
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