[GitHub] [spark] JkSelf commented on a diff in pull request #40914: [SPARK-43240] [SQL] Fix the wrong result issue when calling df.describe() method.

["JkSelf (via GitHub)" <gi...@apache.org>]

JkSelf commented on code in PR #40914:
URL: https://github.com/apache/spark/pull/40914#discussion_r1174741010


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sql/core/src/main/scala/org/apache/spark/sql/execution/stat/StatFunctions.scala:
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@@ -288,7 +288,7 @@ object StatFunctions extends Logging {
     }
 
     // If there is no selected columns, we don't need to run this aggregate, so make it a lazy val.
-    lazy val aggResult = ds.select(aggExprs: _*).queryExecution.toRdd.collect().head
+    lazy val aggResult = ds.select(aggExprs: _*).queryExecution.toRdd.map(_.copy()).collect().head

Review Comment:
    We encountered this issue when passing gluten [ut](https://github.com/apache/spark/blob/0515e6b96fde80f72c5bcedf0d02884bd46450ab/sql/core/src/test/scala/org/apache/spark/sql/DataFrameSuite.scala#L2609). Because in Gluten we rewritten [ColumnarToRow](https://github.com/oap-project/gluten/blob/d9c38e6897f0b94687934cbf5ac68c12cda2bc96/gluten-data/src/main/scala/org/apache/spark/sql/execution/GlutenColumnarToRowExec.scala#L188). which will release the row after the row is used. It seems that this issue is hard to reproduce on apache spark. Because the ColumnarToRow of apache spark is in on heap memory, which is recycled by GC. Do you have any suggestion to reproduce this issue in apache spark? @HyukjinKwon @cloud-fan @zhengruifeng 
   



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