Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/16933#discussion_r104543895
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -562,27 +562,43 @@ object CollapseProject extends Rule[LogicalPlan] {
}
/**
- * Combines adjacent [[Repartition]] and [[RepartitionByExpression]]
operator combinations
- * by keeping only the one.
- * 1. For adjacent [[Repartition]]s, collapse into the last
[[Repartition]].
- * 2. For adjacent [[RepartitionByExpression]]s, collapse into the last
[[RepartitionByExpression]].
- * 3. For a combination of [[Repartition]] and
[[RepartitionByExpression]], collapse as a single
- * [[RepartitionByExpression]] with the expression and last number of
partition.
+ * Combines adjacent [[RepartitionOperation]] operators
*/
object CollapseRepartition extends Rule[LogicalPlan] {
def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
- // Case 1
- case Repartition(numPartitions, shuffle, Repartition(_, _, child)) =>
- Repartition(numPartitions, shuffle, child)
- // Case 2
- case RepartitionByExpression(exprs, RepartitionByExpression(_, child,
_), numPartitions) =>
- RepartitionByExpression(exprs, child, numPartitions)
- // Case 3
- case Repartition(numPartitions, _, r: RepartitionByExpression) =>
- r.copy(numPartitions = numPartitions)
- // Case 3
- case RepartitionByExpression(exprs, Repartition(_, _, child),
numPartitions) =>
- RepartitionByExpression(exprs, child, numPartitions)
+ // Case 1: When a Repartition has a child of Repartition or
RepartitionByExpression,
+ // we can collapse it with the child based on the type of shuffle and
the specified number
+ // of partitions.
+ case r @ Repartition(_, _, child: Repartition) =>
+ collapseRepartition(r, child)
+ case r @ Repartition(_, _, child: RepartitionByExpression) =>
+ collapseRepartition(r, child)
+ // Case 2: When a RepartitionByExpression has a child of Repartition
or RepartitionByExpression
+ // we can remove the child.
+ case r @ RepartitionByExpression(_, child: RepartitionByExpression, _)
=>
+ r.copy(child = child.child)
+ case r @ RepartitionByExpression(_, child: Repartition, _) =>
+ r.copy(child = child.child)
+ }
+
+ /**
+ * Collapses the [[Repartition]] with its child
[[RepartitionOperation]], if possible.
+ * - Case 1 the top [[Repartition]] does not enable shuffle (i.e.,
coalesce API):
+ * If the last numPartitions is bigger, returns the child node;
otherwise, keep unchanged.
+ * - Case 2 the top [[Repartition]] enables shuffle (i.e., repartition
API):
+ * returns the child node with the last numPartitions.
+ */
+ private def collapseRepartition(r: Repartition, child:
RepartitionOperation): LogicalPlan = {
+ (r.shuffle, child.shuffle) match {
+ case (false, true) => child match {
--- End diff --
Yes!
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