Github user ioana-delaney commented on a diff in the pull request:
https://github.com/apache/spark/pull/17546#discussion_r111191433
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/CostBasedJoinReorder.scala
---
@@ -54,8 +54,6 @@ case class CostBasedJoinReorder(conf: SQLConf) extends
Rule[LogicalPlan] with Pr
private def reorder(plan: LogicalPlan, output: Seq[Attribute]):
LogicalPlan = {
val (items, conditions) = extractInnerJoins(plan)
- // TODO: Compute the set of star-joins and use them in the join
enumeration
- // algorithm to prune un-optimal plan choices.
--- End diff --
@viirya Star-schema detection is called from both
```CostBasedJoinReorder``` and ```ReorderJoin```. In the latter case, it is
called to reorder star-joins based on heuristics if cbo is disabled.
When cost-based optimizer becomes the default optimizer, we donât need to
reorder star-joins in ```ReorderJoin``` based on heuristics since the
cost-based optimizer will choose the best plan based on cost.
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