Github user viirya commented on a diff in the pull request:
https://github.com/apache/spark/pull/16578#discussion_r148450632
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetReadSupport.scala
---
@@ -63,9 +74,22 @@ private[parquet] class ParquetReadSupport extends
ReadSupport[UnsafeRow] with Lo
StructType.fromString(schemaString)
}
- val parquetRequestedSchema =
+ val clippedParquetSchema =
ParquetReadSupport.clipParquetSchema(context.getFileSchema,
catalystRequestedSchema)
+ val parquetRequestedSchema = if (parquetMrCompatibility) {
+ // Parquet-mr will throw an exception if we try to read a superset
of the file's schema.
+ // Therefore, we intersect our clipped schema with the underlying
file's schema
--- End diff --
Can you give an example it would fail? We didn't change
`clipParquetSchema`, so I think even when pruning happens, why we read a super
set of the file's schema and cause the exception, according to the comment? We
won't add new fields but remove existing from the file's schema, right?
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