Github user joseph-torres commented on a diff in the pull request:
https://github.com/apache/spark/pull/18790#discussion_r131761258
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -872,6 +886,25 @@ object PushDownPredicate extends Rule[LogicalPlan]
with PredicateHelper {
pushDownPredicate(filter, u.child) { predicate =>
u.withNewChildren(Seq(Filter(predicate, u.child)))
}
+
+ case filter @ Filter(condition, watermark: EventTimeWatermark) =>
--- End diff --
For filter, the logic has a subtle additional condition. We don't want to
push down filters on the watermark attribute, because:
* they'll be at least as expensive to evaluate as the watermark operator
* partition pruning shouldn't apply since there won't be useful partitions
on an event time
For project, I don't see a rule for UnaryNode anywhere. I might have missed
it.
For limit, I actually removed the rule for EventTimeWatermark that I
originally added, since it does drop rows in some situations.
So I don't think that making EventTimeWatermark subclass UnaryNode would
avoid any of the code in this PR. I agree it seems appropriate, but it also
seems orthogonal.
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