Github user sameeragarwal commented on a diff in the pull request:
https://github.com/apache/spark/pull/15319#discussion_r84643784
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala
---
@@ -74,20 +74,98 @@ abstract class QueryPlan[PlanType <:
QueryPlan[PlanType]] extends TreeNode[PlanT
* additional constraint of the form `b = 5`
*/
private def inferAdditionalConstraints(constraints: Set[Expression]):
Set[Expression] = {
+ // Collect alias from expressions to avoid producing non-converging
set of constraints
+ // for recursive functions.
+ //
+ // Don't apply transform on constraints if the replacement will cause
an recursive deduction,
+ // when that happens a non-converging set of constraints will be
created and finally throw
+ // OOM Exception.
+ // For more details, refer to
https://issues.apache.org/jira/browse/SPARK-17733
--- End diff --
This comment doesn't seem to give a lot of context about the underlying
issue. How about we just add a top-level comment for this method summarizing
the issue and remove this? Perhaps, something along the lines of the following:
```scala
/**
* Infers an additional set of constraints from a given set of equality
constraints.
* For e.g., if an operator has constraints of the form (`a = 5`, `a =
b`), this returns an
* additional constraint of the form `b = 5`.
*
* [SPARK-17733] We explicitly prevent producing recursive constraints of
the form `a = f(a, b)`
* as they are often useless and can lead to a non-converging set of
constraints.
*/
private def inferAdditionalConstraints(constraints: Set[Expression]):
Set[Expression]
```
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