cloud-fan commented on a change in pull request #24331: [SPARK-19712][SQL]
Pushdown LeftSemi/LeftAnti below join
URL: https://github.com/apache/spark/pull/24331#discussion_r275453006
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PushDownLeftSemiAntiJoin.scala
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@@ -159,3 +159,102 @@ object PushDownLeftSemiAntiJoin extends
Rule[LogicalPlan] with PredicateHelper {
}
}
}
+
+/**
+ * This rule is a variant of [[PushPredicateThroughJoin]] which can handle
+ * pushing down Left semi and Left Anti joins below a join operator. The
+ * allowable join types are:
+ * 1) Inner
+ * 2) Cross
+ * 3) LeftOuter
+ * 4) RightOuter
+ */
+object PushLeftSemiLeftAntiThroughJoin extends Rule[LogicalPlan] with
PredicateHelper {
+ /**
+ * Define an enumeration to identify whether a LeftSemi/LeftAnti join can be
pushed down to
+ * the left leg or the right leg of the join.
+ */
+ object PushdownDirection extends Enumeration {
+ val TO_LEFT_BRANCH, TO_RIGHT_BRANCH, NONE = Value
+ }
+
+ object AllowedJoin {
+ def unapply(join: Join): Option[Join] = join.joinType match {
+ case Inner | Cross | LeftOuter | RightOuter => Some(join)
+ case _ => None
+ }
+ }
+
+ /**
+ * Determine which side of the join a LeftSemi/LeftAnti join can be pushed
to.
+ */
+ private def pushTo(leftChild: Join, rightChild: LogicalPlan, joinCond:
Option[Expression]) = {
+ val left = leftChild.left
+ val right = leftChild.right
+ val joinType = leftChild.joinType
+ val rightOutput = rightChild.outputSet
+
+ if (joinCond.nonEmpty) {
+ val noPushdown = (PushdownDirection.NONE, None)
+ val conditions = splitConjunctivePredicates(joinCond.get)
+ val (leftConditions, rest) =
+ conditions.partition(_.references.subsetOf(left.outputSet ++
rightOutput))
+ val (rightConditions, commonConditions) =
+ rest.partition(_.references.subsetOf(right.outputSet ++ rightOutput))
+
+ if (rest.isEmpty && leftConditions.nonEmpty) {
+ // When the join conditions can be computed based on the left leg of
+ // leftsemi/anti join then push the leftsemi/anti join to the left
side.
+ (PushdownDirection.TO_LEFT_BRANCH,
leftConditions.reduceLeftOption(And))
+ } else if (leftConditions.isEmpty && rightConditions.nonEmpty &&
commonConditions.isEmpty) {
+ // When the join conditions can be computed based on the attributes
from right leg of
+ // leftsemi/anti join then push the leftsemi/anti join to the right
side.
+ (PushdownDirection.TO_RIGHT_BRANCH,
rightConditions.reduceLeftOption(And))
+ } else {
+ noPushdown
+ }
+ } else {
+ /**
+ * When the join condition is empty,
+ * 1) if this is a left outer join or inner join, push leftsemi/anti
join down
+ * to the left leg of join.
+ * 2) if a right outer join, to the right leg of join,
Review comment:
can you explain it a bit more? what will go wrong if we push right join to
left leg?
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