cloud-fan commented on a change in pull request #29101:
URL: https://github.com/apache/spark/pull/29101#discussion_r455692938
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File path:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/predicates.scala
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@@ -201,126 +201,50 @@ trait PredicateHelper extends Logging {
case e => e.children.forall(canEvaluateWithinJoin)
}
- /**
- * Convert an expression into conjunctive normal form.
- * Definition and algorithm:
https://en.wikipedia.org/wiki/Conjunctive_normal_form
- * CNF can explode exponentially in the size of the input expression when
converting [[Or]]
- * clauses. Use a configuration [[SQLConf.MAX_CNF_NODE_COUNT]] to prevent
such cases.
- *
- * @param condition to be converted into CNF.
- * @return the CNF result as sequence of disjunctive expressions. If the
number of expressions
- * exceeds threshold on converting `Or`, `Seq.empty` is returned.
+ /*
+ * Returns a filter that it's output is a subset of `outputSet` and it
contains all possible
+ * constraints from `condition`. This is used for predicate pushdown.
+ * When there is no such convertible filter, `None` is returned.
*/
- protected def conjunctiveNormalForm(
- condition: Expression,
- groupExpsFunc: Seq[Expression] => Seq[Expression]): Seq[Expression] = {
- val postOrderNodes = postOrderTraversal(condition)
- val resultStack = new mutable.Stack[Seq[Expression]]
- val maxCnfNodeCount = SQLConf.get.maxCnfNodeCount
- // Bottom up approach to get CNF of sub-expressions
- while (postOrderNodes.nonEmpty) {
- val cnf = postOrderNodes.pop() match {
- case _: And =>
- val right = resultStack.pop()
- val left = resultStack.pop()
- left ++ right
- case _: Or =>
- // For each side, there is no need to expand predicates of the same
references.
- // So here we can aggregate predicates of the same qualifier as one
single predicate,
- // for reducing the size of pushed down predicates and corresponding
codegen.
- val right = groupExpsFunc(resultStack.pop())
- val left = groupExpsFunc(resultStack.pop())
- // Stop the loop whenever the result exceeds the `maxCnfNodeCount`
- if (left.size * right.size > maxCnfNodeCount) {
- logInfo(s"As the result size exceeds the threshold
$maxCnfNodeCount. " +
- "The CNF conversion is skipped and returning Seq.empty now. To
avoid this, you can " +
- s"raise the limit ${SQLConf.MAX_CNF_NODE_COUNT.key}.")
- return Seq.empty
- } else {
- for { x <- left; y <- right } yield Or(x, y)
- }
- case other => other :: Nil
+ protected def convertibleFilter(
Review comment:
the name is bit weird. `extractPredicatesWithinOutputSet`?
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