[GitHub] [spark] Yaohua628 commented on a change in pull request #34575: [SPARK-37273][SQL] Support hidden file metadata columns in Spark SQL

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Yaohua628 commented on a change in pull request #34575:
URL: https://github.com/apache/spark/pull/34575#discussion_r772754324



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/SchemaPruning.scala
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@@ -164,7 +164,12 @@ object SchemaPruning extends Rule[LogicalPlan] {
       outputRelation: LogicalRelation,
       prunedBaseRelation: HadoopFsRelation) = {
     val prunedOutput = getPrunedOutput(outputRelation.output, prunedBaseRelation.schema)
-    outputRelation.copy(relation = prunedBaseRelation, output = prunedOutput)
+    // also add the metadata output if any
+    // TODO: should be able to prune the metadata schema

Review comment:
       actually no:
   1. this rule supports only: `Parquet` + `ORC` and controls by a flag `spark.sql.optimizer.nestedSchemaPruning.enabled`
   2. this rule only prunes the data schema (comparing the data schema with the project + filter)
   
   I am thinking:
   - refactor this rule to prune metadata
   OR
   - make a new rule `MetadataSchemaPruning`
   OR
   - prune the metadata at `FileSourceStrategy` (might be hacky)




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