[GitHub] [spark] gengliangwang commented on a change in pull request #24043: [SPARK-11412][SQL] Support merge schema for ORC

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

gengliangwang commented on a change in pull request #24043: [SPARK-11412][SQL] Support merge schema for ORC
URL: https://github.com/apache/spark/pull/24043#discussion_r288671013
 
 

 ##########
 File path: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/orc/OrcUtils.scala
 ##########
 @@ -82,14 +83,95 @@ object OrcUtils extends Logging {
       : Option[StructType] = {
     val ignoreCorruptFiles = sparkSession.sessionState.conf.ignoreCorruptFiles
     val conf = sparkSession.sessionState.newHadoopConf()
-    // TODO: We need to support merge schema. Please see SPARK-11412.
     files.toIterator.map(file => readSchema(file.getPath, conf, ignoreCorruptFiles)).collectFirst {
       case Some(schema) =>
         logDebug(s"Reading schema from file $files, got Hive schema string: $schema")
         CatalystSqlParser.parseDataType(schema.toString).asInstanceOf[StructType]
     }
   }
 
+  /**
+   * Read single ORC file schema using native version of ORC
+   */
+  def singleFileSchemaReader(file: String, conf: Configuration, ignoreCorruptFiles: Boolean)
+      : Option[StructType] = {
+    OrcUtils.readSchema(new Path(file), conf, ignoreCorruptFiles)
+      .map(s => CatalystSqlParser.parseDataType(s.toString).asInstanceOf[StructType])
+  }
+
+  /**
+   * Figures out a merged ORC schema with a distributed Spark job.
+   */
+  def mergeSchemasInParallel(
+      sparkSession: SparkSession,
+      files: Seq[FileStatus],
+      singleFileSchemaReader: (String, Configuration, Boolean) => Option[StructType])
+      : Option[StructType] = {
+    val serializedConf = new SerializableConfiguration(sparkSession.sessionState.newHadoopConf())
+
+    val filePaths = files.map(_.getPath.toString)
+
+    // Set the number of partitions to prevent following schema reads from generating many tasks
+    // in case of a small number of orc files.
+    val numParallelism = Math.min(Math.max(filePaths.size, 1),
+      sparkSession.sparkContext.defaultParallelism)
+
+    val ignoreCorruptFiles = sparkSession.sessionState.conf.ignoreCorruptFiles
+
+    // Issues a Spark job to read ORC schema in parallel.
+    val partiallyMergedSchemas =
 
 Review comment:
   Nit: the following code has a lot in common with https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/ParquetFileFormat.scala#L600
   
   Could you try abstracting some of them?

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