cloud-fan commented on code in PR #52468:
URL: https://github.com/apache/spark/pull/52468#discussion_r2382544056
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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ApplyLimitAll.scala:
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@@ -20,6 +20,15 @@ package org.apache.spark.sql.catalyst.analysis
import org.apache.spark.sql.catalyst.plans.logical.{Aggregate, BaseEvalPython,
CTERelationRef, Filter, Join, LimitAll, LogicalPlan, Offset, Project,
SubqueryAlias, Union, Window}
import org.apache.spark.sql.catalyst.rules.Rule
+/**
+ * Limit All is usually a no-op operation in spark, used for compatibility
with other database
+ * systems. However, in the case of recursive CTEs there is a default value
(controlled by a flag)
+ * of the maximum number of rows that a recursive CTE may return, which can be
overridden by a Limit
+ * operator above the UnionLoop node. Since this is a case where a Limit
operator actually increases
+ * the number of rows a node should return, Limit All stops being a no-op node
semantically, and
+ * should be used to enable unlimited looping in recursive CTEs.
+ */
+
Review Comment:
```suggestion
```
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