[GitHub] [spark] cloud-fan commented on a diff in pull request #42315: [SPARK-44653][SQL] Non-trivial DataFrame unions should not break caching

["cloud-fan (via GitHub)" <gi...@apache.org>]

cloud-fan commented on code in PR #42315:
URL: https://github.com/apache/spark/pull/42315#discussion_r1283875186


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sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala:
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@@ -157,7 +157,7 @@ abstract class Optimizer(catalogManager: CatalogManager)
     //   since the other rules might make two separate Unions operators adjacent.
     Batch("Inline CTE", Once,
       InlineCTE()) ::
-    Batch("Union", Once,
+    Batch("Union", fixedPoint,

Review Comment:
   Without the pre-optimization in the dataframe side, some pyspark tests failed complaining that this batch is not idempotent. In fact, this optimization batch does not need to be idempotent, we use `Once` before because we thought it was sufficient, but it's actually not sufficient.



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