[GitHub] dilipbiswal commented on a change in pull request #23822: [MINOR][DOC] Add note regarding proper usage of QueryExecution.toRdd

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dilipbiswal commented on a change in pull request #23822: [MINOR][DOC] Add note regarding proper usage of QueryExecution.toRdd
URL: https://github.com/apache/spark/pull/23822#discussion_r257810361
 
 

 ##########
 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/QueryExecution.scala
 ##########
 @@ -85,7 +85,14 @@ class QueryExecution(
     prepareForExecution(sparkPlan)
   }
 
-  /** Internal version of the RDD. Avoids copies and has no schema */
+  /**
+   * Internal version of the RDD. Avoids copies and has no schema.
+   * Note for callers: Spark may apply various optimization including reusing object: this means
+   * the row is valid only for the iteration it is retrieved. You should avoid storing row and
+   * accessing after iteration. (Calling `collect()` is one of known bad usage.)
+   * If you want to store these rows into collection, please apply some converter or copy row
+   * which produces new object per iteration.
+   */
 
 Review comment:
   @HeartSaVioR Should we point the users to dataset.rdd method where the conversion is already applied ?

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