cloud-fan commented on a change in pull request #32602:
URL: https://github.com/apache/spark/pull/32602#discussion_r780377367
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/PropagateEmptyRelation.scala
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@@ -137,3 +125,55 @@ object PropagateEmptyRelation extends Rule[LogicalPlan]
with PredicateHelper wit
}
}
}
+
+/**
+ * This rule runs in the normal optimizer and optimizes more cases
+ * compared to [[PropagateEmptyRelationBase]]:
+ * 1. Higher-node Logical Plans
+ * - Union with all empty children.
+ * 2. Unary-node Logical Plans
+ * - Project/Filter/Sample with all empty children.
+ *
+ * The reason why we don't apply this rule at AQE optimizer side is: the
benefit is not big enough
+ * and it may introduce extra exchanges.
Review comment:
After more thought, I think this is a big performance issue if we can't
propagate empty relations through project/filter which are quite common. The
risk of introducing new shuffles is relatively small compared to this.
@ulysses-you can we move all the logic to `PropagateEmptyRelationBase`?
`PropagateEmptyRelation` should not have any extra logic.
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