[GitHub] [spark] dongjoon-hyun commented on a change in pull request #24221: [SPARK-27248][SQL] `refreshTable` should recreate cache with same cache name and storage level

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dongjoon-hyun commented on a change in pull request #24221: [SPARK-27248][SQL] `refreshTable` should recreate cache with same cache name and storage level
URL: https://github.com/apache/spark/pull/24221#discussion_r281361672
 
 

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 File path: docs/sql-migration-guide-upgrade.md
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 @@ -50,6 +50,8 @@ license: |
 
   - In Spark version 2.4 and earlier, JSON datasource and JSON functions like `from_json` convert a bad JSON record to a row with all `null`s in the PERMISSIVE mode when specified schema is `StructType`. Since Spark 3.0, the returned row can contain non-`null` fields if some of JSON column values were parsed and converted to desired types successfully.
 
+  - Refreshing a cached table would trigger a table uncache operation and then a table cache (lazily) operation. In Spark version 2.4 and earlier, the cache name and storage level are not preserved before the uncache operation. Therefore, the cache name and storage level could be changed unexpectedly. Since Spark 3.0, cache name and storage level will be first preserved for cache recreation. It helps to maintain a consistent cache behavior upon table refreshing.
 
 Review comment:
   ```
   - the cache name and storage level are not preserved before the uncache operation.
   - the cache name and storage level are not preserved.
   ```

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