Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/16245#discussion_r97211371
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
---
@@ -514,6 +514,34 @@ case class OptimizeCodegen(conf: CatalystConf) extends
Rule[LogicalPlan] {
/**
+ * Reorders the predicates in `Filter` so more expensive expressions like
UDF can evaluate later.
+ */
+object ReorderPredicatesInFilter extends Rule[LogicalPlan] with
PredicateHelper {
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case f @ Filter(pred, child) =>
+ // Extracts deterministic suffix expressions from Filter predicate.
+ val expressions = splitConjunctivePredicates(pred)
+ // The beginning index of the deterministic suffix expressions.
+ var splitIndex = -1
+ (expressions.length - 1 to 0 by -1).foreach { idx =>
+ if (splitIndex == -1 && !expressions(idx).deterministic) {
+ splitIndex = idx + 1
+ }
+ }
+ if (splitIndex == expressions.length) {
+ // All expressions are non-deterministic, no reordering.
+ f
+ } else {
+ val (nonDeterminstics, deterministicExprs) =
expressions.splitAt(splitIndex)
--- End diff --
Reordering non-deterministic expressions might change the evaluation
results. I think `foldable` expressions are handled by other rule already. And
I remember we don't have explicit `stateful` expression or it is classified as
`non-deterministic` too.
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