Gengliang Wang created SPARK-26915:
--------------------------------------
Summary: File source should write without schema inference and
validation in DataFrameWriter.save()
Key: SPARK-26915
URL: https://issues.apache.org/jira/browse/SPARK-26915
Project: Spark
Issue Type: Task
Components: SQL
Affects Versions: 3.0.0
Reporter: Gengliang Wang
Spark supports writing to file data sources without getting and validation with
the table schema.
For example,
```
spark.range(10).write.orc(path)
val newDF = spark.range(20).map(id => (id.toDouble,
id.toString)).toDF("double", "string")
newDF.write.mode("overwrite").orc(path)
```
1. There is no need to get/infer the schema from the table/path
2. The schema of `newDF` can be different with the original table schema.
However, from https://github.com/apache/spark/pull/23606/files#r255319992 we
can see that the feature above is missing in data source V2. Currently, data
source V2 always validates the output query with the table schema. Even after
the catalog support of DS V2 is implemented, I think it is hard to support both
behaviors with the current API/framework.
This PR proposes to process file sources as a special case in
`DataFrameWriter.save()`. So that we can keep the original behavior for this
DataFrame API.
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