Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/23248#discussion_r240041688
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/python/ExtractPythonUDFs.scala
---
@@ -131,8 +131,20 @@ object ExtractPythonUDFs extends Rule[LogicalPlan]
with PredicateHelper {
expressions.flatMap(collectEvaluableUDFs)
}
- def apply(plan: LogicalPlan): LogicalPlan = plan transformUp {
- case plan: LogicalPlan => extract(plan)
+ def apply(plan: LogicalPlan): LogicalPlan = plan match {
+ // SPARK-26293: A subquery will be rewritten into join later, and will
go through this rule
+ // eventually. Here we skip subquery, as Python UDF only needs to be
extracted once.
+ case _: Subquery => plan
--- End diff --
I'm not sure if it is totally ok to skip `Subquery` for all optimizer rules.
For `ExtractPythonUDFs` I think it is ok because `ExtractPythonUDFs` is
performed after the rules in `RewriteSubquery`. So we can skip
`ExtractPythonUDFs` here and extract Python UDF after the subqueries are
rewritten into join.
But for the rules which perform before `RewriteSubquery`, if we skip it on
`Subquery`, we have no chance to do the rules after the subqueries are
rewritten into join.
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