[GitHub] [spark] maropu commented on a change in pull request #30156: [SPARK-33248][SQL] Add a configuration to control the legacy behavior of whether need to pad null value when value size less then schema size

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maropu commented on a change in pull request #30156:
URL: https://github.com/apache/spark/pull/30156#discussion_r512695698



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File path: docs/sql-migration-guide.md
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@@ -49,6 +49,8 @@ license: |
   - In Spark 3.1, we remove the built-in Hive 1.2. You need to migrate your custom SerDes to Hive 2.3. See [HIVE-15167](https://issues.apache.org/jira/browse/HIVE-15167) for more details.
   
   - In Spark 3.1, loading and saving of timestamps from/to parquet files fails if the timestamps are before 1900-01-01 00:00:00Z, and loaded (saved) as the INT96 type. In Spark 3.0, the actions don't fail but might lead to shifting of the input timestamps due to rebasing from/to Julian to/from Proleptic Gregorian calendar. To restore the behavior before Spark 3.1, you can set `spark.sql.legacy.parquet.int96RebaseModeInRead` or/and `spark.sql.legacy.parquet.int96RebaseModeInWrite` to `LEGACY`.
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+  - In Spark 3.1, when `spark.sql.legacy.transformationPadNullWhenValueLessThenSchema` is true, Spark will pad NULL value when scrip transformation's output value size less then schema size in default-serde mode. If false, we will keep behavior as before.

Review comment:
       Could you describe what's `behavior as before`?




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