[GitHub] [spark] Yaohua628 commented on a diff in pull request #36851: [SPARK-39535][SQL] Make `SchemaPruning` only pruning if it contains nested column

[GitBox <gi...@apache.org>]

Yaohua628 commented on code in PR #36851:
URL: https://github.com/apache/spark/pull/36851#discussion_r906283197


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sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/SchemaPruning.scala:
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@@ -103,8 +104,14 @@ object SchemaPruning extends Rule[LogicalPlan] {
     }
   }
 
+  private def containsNestedColumn(fsRelation: HadoopFsRelation): Boolean =

Review Comment:
   Maybe you can have one more check here "if it contains `_metadata`" using `FileSourceMetadataAttribute(attr)` and add a test for it? That would be great!



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sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/SchemaPruning.scala:
##########
@@ -103,8 +104,14 @@ object SchemaPruning extends Rule[LogicalPlan] {
     }
   }
 
+  private def containsNestedColumn(fsRelation: HadoopFsRelation): Boolean =

Review Comment:
   I think it will break the schema pruning for the hidden metadata struct (`_metadata` is not in `fsRelation.schema` but `fsRelation.output`). 
   
   We actually have tests for that ([here](https://github.com/apache/spark/blob/master/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/FileMetadataStructSuite.scala#L431)): The reason why they didn't break is the test data itself luckily has a nested column ([here](https://github.com/apache/spark/blob/master/sql/core/src/test/scala/org/apache/spark/sql/execution/datasources/FileMetadataStructSuite.scala#L37)).



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