[GitHub] [spark] HyukjinKwon commented on a change in pull request #27622: [SPARK-27528][followup] improve migration guide

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HyukjinKwon commented on a change in pull request #27622: [SPARK-27528][followup] improve migration guide
URL: https://github.com/apache/spark/pull/27622#discussion_r381148789
 
 

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 File path: docs/sql-migration-guide.md
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 @@ -87,7 +87,7 @@ license: |
 
   - In Spark version 2.4, when a spark session is created via `cloneSession()`, the newly created spark session inherits its configuration from its parent `SparkContext` even though the same configuration may exist with a different value in its parent spark session. Since Spark 3.0, the configurations of a parent `SparkSession` have a higher precedence over the parent `SparkContext`. The old behavior can be restored by setting `spark.sql.legacy.sessionInitWithConfigDefaults` to `true`.
 
-  - Since Spark 3.0, parquet logical type `TIMESTAMP_MICROS` is used by default while saving `TIMESTAMP` columns. In Spark version 2.4 and earlier, `TIMESTAMP` columns are saved as `INT96` in parquet files. To set `INT96` to `spark.sql.parquet.outputTimestampType` restores the previous behavior.
+  - Since Spark 3.0, parquet logical type `TIMESTAMP_MICROS` is used by default while saving `TIMESTAMP` columns. In Spark version 2.4 and earlier, `TIMESTAMP` columns are saved as `INT96` in parquet files. Note that, some SQL systems like Impala 2.x can only read `INT96` timestamps, you can set `spark.sql.parquet.outputTimestampType` as `INT96` to restore the previous behavior and keep interoperability.
 
 Review comment:
   Shouldn't we maybe mention Hive first rather than Impala?

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