HeartSaVioR 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_r257817130
##########
File path:
sql/core/src/main/scala/org/apache/spark/sql/execution/QueryExecution.scala
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@@ -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:
Yeah that's good suggestion for end users (not Spark developers). Will add.
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