Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/23208#discussion_r240028515
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/TableProvider.java ---
@@ -25,7 +25,10 @@
* The base interface for v2 data sources which don't have a real catalog.
Implementations must
* have a public, 0-arg constructor.
* <p>
- * The major responsibility of this interface is to return a {@link Table}
for read/write.
+ * The major responsibility of this interface is to return a {@link Table}
for read/write. If you
+ * want to allow end-users to write data to non-existing tables via write
APIs in `DataFrameWriter`
+ * with `SaveMode`, you must return a {@link Table} instance even if the
table doesn't exist. The
+ * table schema can be empty in this case.
--- End diff --
I'm not convinced it's safe to remove `SaveMode` right away, when there is
only an `Append` operator implemented currently.
If we do it, it means `DataFrameWriter.save` need to throw an exception for
a lot of cases, except when the `mode` is append. I don't think this is
acceptable right now.
Can we discuss the removal of `SaveMode` at least after all the necessary
new write operators are implemented?
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