Github user cloud-fan commented on a diff in the pull request: https://github.com/apache/spark/pull/17289#discussion_r106114894 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/DataFrameWriter.scala --- @@ -319,6 +319,10 @@ final class DataFrameWriter[T] private[sql](ds: Dataset[T]) { * +---+---+ * }}} * + * The external catalog (Hive metastore) is used to determine if the table exists. --- End diff -- ``` In this method, save mode is used to determine the behavior if the data source table exists in Spark catalog. We will always overwrite the underlying data of data source(e.g. a table in JDBC data source) if the table doesn't exist in Spark catalog, and will always append to the underlying data of data source if the table already exists. ```
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