cloud-fan commented on a change in pull request #29101:
URL: https://github.com/apache/spark/pull/29101#discussion_r455909295
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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 +201,51 @@ 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.
Review comment:
`it contains all possible constraints from condition` -> `it's a
precondition to satisfy the given condition`
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