[3.3] allow user-specified schema in read if it's consistent (#3929) #4125
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backport #3929 to 3.3
Which Delta project/connector is this regarding?
Description
User-specified schema may come from the catalog if the Delta table is stored in an external catalog that syncs the table schema with the Delta log. We should allow it if it's the same as the real Delta table schema.
This is already the case for batch read, see apache/spark#15046
This PR changes the Delta streaming read to allow it as well.
Note: since Delta uses DS v2 (
TableProvider) and explicitly claims that user-specified schema is not supported (TableProvider#supportsExternalMetadatareturns false by default), end users still can't specify schema inspark.read/readStream.schema. This change is only for advanced Spark plugins that can construct logical plans to triggers Delta v1 source stream scan.How was this patch tested?
a new test
Does this PR introduce any user-facing changes?
No