Github user liancheng commented on a diff in the pull request:
https://github.com/apache/spark/pull/10444#discussion_r48332590
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala
---
@@ -47,6 +48,34 @@ trait Predicate extends Expression {
override def dataType: DataType = BooleanType
}
+object Predicate extends PredicateHelper {
+ def toCNF(predicate: Expression, maybeThreshold: Option[Double] = None):
Expression = {
+ val cnf = new CNFExecutor(predicate).execute(predicate)
+ val threshold = maybeThreshold.map(predicate.size *
_).getOrElse(Double.MaxValue)
+ if (cnf.size > threshold) predicate else cnf
--- End diff --
When the threshold is exceeded, the original predicate rather than the
intermediate converted predicate is returned. This because the intermediate
result may not be in CNF, thus:
1. It doesn't bring much benefit for filter push-down, and
2. It's much larger than the original predicate and brings extra evaluation
cost.
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