[GitHub] gengliangwang commented on issue #23836: [SPARK-26915][SQL] DataFrameWriter.save() should write without schema validation

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gengliangwang commented on issue #23836: [SPARK-26915][SQL] DataFrameWriter.save()  should write without schema validation
URL: https://github.com/apache/spark/pull/23836#issuecomment-465428121
 
 
   @rdblue Sorry if I cause some misunderstanding.
   Let's focus on the API `DataFrameWriter.save` here:
   1. The expressions `AppendData` and `OverwriteByExpression` always get table schema and validate the output schema with table schema. This is a serious behavior change.  Before we have a final agreement about file source V2 behavior(mostly likely we will keep the V1 behavior in this API), I would suggest to revert them for now.
   
   2. Keeping ORC V2 working helps us to find problems. This PR is not proposing to keep `SupportsSaveMode` or to saying this is the final solution. I am suggesting that we should keep file source behavior in this API. Unless there is a clear solution that eventually the following partial development will work.
   
   The above solution of @cloud-fan is good directions to go. We can discuss the solution in tomorrow's meetup. 
   For the code changes in `DataFrameWriter.save`, I think we should remove the new expressions for now.

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