[SPARK-28366][CORE] Logging in driver when loading single large unsplittable file

core/src/main/scala/org/apache/spark/internal/config/package.scala

@@ -1180,6 +1180,14 @@ package object config {
       .intConf
       .createWithDefault(1)
 
+  private[spark] val IO_WARNING_LARGEFILETHRESHOLD =
+    ConfigBuilder("spark.io.warning.largeFileThreshold")
+      .internal()
+      .doc("When spark loading one single large file, if file size exceed this " +
+        "threshold, then log warning with possible reasons.")
+      .longConf
+      .createWithDefault(1024 * 1024 * 1024)
+
   private[spark] val EVENT_LOG_COMPRESSION_CODEC =
     ConfigBuilder("spark.eventLog.compression.codec")
       .doc("The codec used to compress event log. By default, Spark provides four codecs: " +

core/src/main/scala/org/apache/spark/rdd/HadoopRDD.scala

@@ -25,6 +25,7 @@ import scala.collection.immutable.Map
 import scala.reflect.ClassTag
 
 import org.apache.hadoop.conf.{Configurable, Configuration}
+import org.apache.hadoop.io.compress.{CompressionCodecFactory, SplittableCompressionCodec}
 import org.apache.hadoop.mapred._
 import org.apache.hadoop.mapred.lib.CombineFileSplit
 import org.apache.hadoop.mapreduce.TaskType
@@ -40,7 +41,7 @@ import org.apache.spark.internal.config._
 import org.apache.spark.rdd.HadoopRDD.HadoopMapPartitionsWithSplitRDD
 import org.apache.spark.scheduler.{HDFSCacheTaskLocation, HostTaskLocation}
 import org.apache.spark.storage.StorageLevel
-import org.apache.spark.util.{NextIterator, SerializableConfiguration, ShutdownHookManager}
+import org.apache.spark.util.{NextIterator, SerializableConfiguration, ShutdownHookManager, Utils}
 
 /**
  * A Spark split class that wraps around a Hadoop InputSplit.
@@ -207,6 +208,21 @@ class HadoopRDD[K, V](
       } else {
         allInputSplits
       }
+      if (inputSplits.length == 1 && inputSplits(0).isInstanceOf[FileSplit]) {
+        val fileSplit = inputSplits(0).asInstanceOf[FileSplit]
+        val path = fileSplit.getPath
+        if (fileSplit.getLength > conf.get(IO_WARNING_LARGEFILETHRESHOLD)) {
+          val codecFactory = new CompressionCodecFactory(jobConf)
+          if (Utils.isFileSplittable(path, codecFactory)) {
+            logWarning(s"Loading one large file ${path.toString} with only one partition, " +
+              s"we can increase partition numbers by the `minPartitions` argument in method " +
+              "`sc.textFile`")
+          } else {
+            logWarning(s"Loading one large unsplittable file ${path.toString} with only one " +
+              s"partition, because the file is compressed by unsplittable compression codec.")
+          }
+        }
+      }
       val array = new Array[Partition](inputSplits.size)
       for (i <- 0 until inputSplits.size) {
         array(i) = new HadoopPartition(id, i, inputSplits(i))

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -51,6 +51,7 @@ import com.google.common.net.InetAddresses
 import org.apache.commons.lang3.SystemUtils
 import org.apache.hadoop.conf.Configuration
 import org.apache.hadoop.fs.{FileSystem, FileUtil, Path}
+import org.apache.hadoop.io.compress.{CompressionCodecFactory, SplittableCompressionCodec}
 import org.apache.hadoop.security.UserGroupInformation
 import org.apache.hadoop.yarn.conf.YarnConfiguration
 import org.eclipse.jetty.util.MultiException
@@ -2895,6 +2896,12 @@ private[spark] object Utils extends Logging {
   def isLocalUri(uri: String): Boolean = {
     uri.startsWith(s"$LOCAL_SCHEME:")
   }
+
+  /** Check whether the file of the path is splittable. */
+  def isFileSplittable(path: Path, codecFactory: CompressionCodecFactory): Boolean = {
+    val codec = codecFactory.getCodec(path)
+    codec == null || codec.isInstanceOf[SplittableCompressionCodec]
+  }
 }
 
 private[util] object CallerContext extends Logging {

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/FileScan.scala

@@ -21,29 +21,40 @@ import java.util.{Locale, OptionalLong}
 import org.apache.commons.lang3.StringUtils
 import org.apache.hadoop.fs.Path
 
+import org.apache.spark.internal.Logging
+import org.apache.spark.internal.config.IO_WARNING_LARGEFILETHRESHOLD
 import org.apache.spark.sql.{AnalysisException, SparkSession}
-import org.apache.spark.sql.catalyst.expressions.AttributeReference
 import org.apache.spark.sql.catalyst.expressions.codegen.GenerateUnsafeProjection
 import org.apache.spark.sql.execution.PartitionedFileUtil
 import org.apache.spark.sql.execution.datasources._
 import org.apache.spark.sql.sources.Filter
 import org.apache.spark.sql.sources.v2.reader._
 import org.apache.spark.sql.types.StructType
-import org.apache.spark.sql.util.CaseInsensitiveStringMap
 import org.apache.spark.util.Utils
 
 abstract class FileScan(
     sparkSession: SparkSession,
     fileIndex: PartitioningAwareFileIndex,
     readDataSchema: StructType,
-    readPartitionSchema: StructType) extends Scan with Batch with SupportsReportStatistics {
+    readPartitionSchema: StructType)
+  extends Scan
+  with Batch with SupportsReportStatistics with Logging {
   /**
    * Returns whether a file with `path` could be split or not.
    */
   def isSplitable(path: Path): Boolean = {
     false
   }
 
+  /**
+   * If a file with `path` is unsplittable, return the unsplittable reason,
+   * otherwise return `None`.
+   */
+  def getFileUnSplittableReason(path: Path): String = {
+    assert(!isSplitable(path))
+    "undefined"
+  }
+
   override def description(): String = {
     val locationDesc =
       fileIndex.getClass.getSimpleName + fileIndex.rootPaths.mkString("[", ", ", "]")
@@ -91,6 +102,16 @@ abstract class FileScan(
         )
       }.toArray.sortBy(_.length)(implicitly[Ordering[Long]].reverse)
     }
+
+    if (splitFiles.length == 1) {
+      val path = new Path(splitFiles(0).filePath)
+      if (!isSplitable(path) && splitFiles(0).length >
+        sparkSession.sparkContext.getConf.get(IO_WARNING_LARGEFILETHRESHOLD)) {
+        logWarning(s"Loading one large unsplittable file ${path.toString} with only one " +
+          s"partition, the reason is: ${getFileUnSplittableReason(path)}")
+      }
+    }
+
     FilePartition.getFilePartitions(sparkSession, splitFiles, maxSplitBytes)
   }
 

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/TextBasedFileScan.scala

@@ -19,12 +19,13 @@ package org.apache.spark.sql.execution.datasources.v2
 import scala.collection.JavaConverters._
 
 import org.apache.hadoop.fs.Path
-import org.apache.hadoop.io.compress.{CompressionCodecFactory, SplittableCompressionCodec}
+import org.apache.hadoop.io.compress.CompressionCodecFactory
 
 import org.apache.spark.sql.SparkSession
 import org.apache.spark.sql.execution.datasources.PartitioningAwareFileIndex
 import org.apache.spark.sql.types.StructType
 import org.apache.spark.sql.util.CaseInsensitiveStringMap
+import org.apache.spark.util.Utils
 
 abstract class TextBasedFileScan(
     sparkSession: SparkSession,
@@ -33,14 +34,13 @@ abstract class TextBasedFileScan(
     readPartitionSchema: StructType,
     options: CaseInsensitiveStringMap)
   extends FileScan(sparkSession, fileIndex, readDataSchema, readPartitionSchema) {
-  private var codecFactory: CompressionCodecFactory = _
+  @transient private lazy val codecFactory: CompressionCodecFactory = new CompressionCodecFactory(
+    sparkSession.sessionState.newHadoopConfWithOptions(options.asScala.toMap))
 
-  override def isSplitable(path: Path): Boolean = {
-    if (codecFactory == null) {
-      codecFactory = new CompressionCodecFactory(
-        sparkSession.sessionState.newHadoopConfWithOptions(options.asScala.toMap))
-    }
-    val codec = codecFactory.getCodec(path)
-    codec == null || codec.isInstanceOf[SplittableCompressionCodec]
+  override def isSplitable(path: Path): Boolean = Utils.isFileSplittable(path, codecFactory)
+
+  override def getFileUnSplittableReason(path: Path): String = {
+    assert(!isSplitable(path))
+    "the file is compressed by unsplittable compression codec"
   }
 }

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/csv/CSVScan.scala

@@ -24,7 +24,7 @@ import org.apache.spark.sql.{AnalysisException, SparkSession}
 import org.apache.spark.sql.catalyst.csv.CSVOptions
 import org.apache.spark.sql.catalyst.expressions.ExprUtils
 import org.apache.spark.sql.execution.datasources.PartitioningAwareFileIndex
-import org.apache.spark.sql.execution.datasources.csv.CSVDataSource
+import org.apache.spark.sql.execution.datasources.csv.{CSVDataSource, MultiLineCSVDataSource}
 import org.apache.spark.sql.execution.datasources.v2.TextBasedFileScan
 import org.apache.spark.sql.sources.v2.reader.PartitionReaderFactory
 import org.apache.spark.sql.types.{DataType, StructType}
@@ -50,6 +50,15 @@ case class CSVScan(
     CSVDataSource(parsedOptions).isSplitable && super.isSplitable(path)
   }
 
+  override def getFileUnSplittableReason(path: Path): String = {
+    assert(!isSplitable(path))
+    if (!super.isSplitable(path)) {
+      super.getFileUnSplittableReason(path)
+    } else {
+      "the csv datasource is set multiLine mode"
+    }
+  }
+
   override def createReaderFactory(): PartitionReaderFactory = {
     // Check a field requirement for corrupt records here to throw an exception in a driver side
     ExprUtils.verifyColumnNameOfCorruptRecord(dataSchema, parsedOptions.columnNameOfCorruptRecord)

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/json/JsonScan.scala

@@ -50,6 +50,15 @@ case class JsonScan(
     JsonDataSource(parsedOptions).isSplitable && super.isSplitable(path)
   }
 
+  override def getFileUnSplittableReason(path: Path): String = {
+    assert(!isSplitable(path))
+    if (!super.isSplitable(path)) {
+      super.getFileUnSplittableReason(path)
+    } else {
+      "the json datasource is set multiLine mode"
+    }
+  }
+
   override def createReaderFactory(): PartitionReaderFactory = {
     // Check a field requirement for corrupt records here to throw an exception in a driver side
     ExprUtils.verifyColumnNameOfCorruptRecord(dataSchema, parsedOptions.columnNameOfCorruptRecord)

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/v2/text/TextScan.scala

@@ -44,6 +44,15 @@ case class TextScan(
     super.isSplitable(path) && !textOptions.wholeText
   }
 
+  override def getFileUnSplittableReason(path: Path): String = {
+    assert(!isSplitable(path))
+    if (!super.isSplitable(path)) {
+      super.getFileUnSplittableReason(path)
+    } else {
+      "the text datasource is set wholetext mode"
+    }
+  }
+
   override def createReaderFactory(): PartitionReaderFactory = {
     assert(
       readDataSchema.length <= 1,