Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/11235#discussion_r55457081
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -146,6 +147,56 @@ object EliminateSerialization extends
Rule[LogicalPlan] {
}
/**
+ * Add Filter to left and right of a EquiJoin to filter out rows with null
keys.
+ * So we may not need to check nullability of keys while joining. Besides,
by filtering
+ * out keys with null, we can also reduce data size in Join.
+ */
+object AddNullFilterForEquiJoin extends Rule[LogicalPlan] with
PredicateHelper {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case ExtractEquiJoinKeys(Inner, leftKeys, rightKeys, condition, left,
right) =>
+ val leftConditions = leftKeys.distinct.map { l =>
+ IsNotNull(l)
+ }.reduceLeft(And)
+
+ val rightConditions = rightKeys.distinct.map { r =>
+ IsNotNull(r)
+ }.reduceLeft(And)
+
+ val keysConditions = ExpressionSet(leftKeys.zip(rightKeys).map { lr
=>
+ EqualTo(lr._2, lr._1)
+ }).reduceLeft(And)
+
+ val finalConditions = if (condition.isDefined) {
+ And(keysConditions, condition.get)
+ } else {
+ keysConditions
+ }
+
+ val leftHasAllNotNullPredicate = left.constraints.nonEmpty &&
+ left.constraints.filter(_.isInstanceOf[IsNotNull])
+ .forall(expr =>
leftConditions.references.intersect(expr.references).nonEmpty)
+
+ val rightHasAllNotNullPredicate = right.constraints.nonEmpty &&
+ right.constraints.filter(_.isInstanceOf[IsNotNull])
+ .forall(expr =>
rightConditions.references.intersect(expr.references).nonEmpty)
--- End diff --
Because we want to eliminate reading nulls in advance of join operator. If
we simply add IsNotNull to the left/right to the conditions, the nulls are
still read during performing join.
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