[SPARK-14838] [SQL] Set default size for ObjecType to avoid failure w…

…hen estimating sizeInBytes in ObjectProducer

## What changes were proposed in this pull request?

We have logical plans that produce domain objects which are `ObjectType`. As we can't estimate the size of `ObjectType`, we throw an `UnsupportedOperationException` if trying to do that. We should set a default size for `ObjectType` to avoid this failure.

## How was this patch tested?

`DatasetSuite`.

Author: Liang-Chi Hsieh <simonh@tw.ibm.com>

Closes #12599 from viirya/skip-broadcast-objectproducer.

sql/catalyst/src/main/scala/org/apache/spark/sql/types/ObjectType.scala

@@ -37,8 +37,7 @@ private[sql] object ObjectType extends AbstractDataType {
  * outside of the execution engine.
  */
 private[sql] case class ObjectType(cls: Class[_]) extends DataType {
-  override def defaultSize: Int =
-    throw new UnsupportedOperationException("No size estimation available for objects.")
+  override def defaultSize: Int = 4096
 
   def asNullable: DataType = this
 

sql/core/src/test/scala/org/apache/spark/sql/DatasetSuite.scala

@@ -630,6 +630,29 @@ class DatasetSuite extends QueryTest with SharedSQLContext {
     // Make sure the generated code for this plan can compile and execute.
     checkDataset(wideDF.map(_.getLong(0)), 0L until 10 : _*)
   }
+
+  test("SPARK-14838: estimating sizeInBytes in operators with ObjectProducer shouldn't fail") {
+    val dataset = Seq(
+      (0, 3, 54f),
+      (0, 4, 44f),
+      (0, 5, 42f),
+      (1, 3, 39f),
+      (1, 5, 33f),
+      (1, 4, 26f),
+      (2, 3, 51f),
+      (2, 5, 45f),
+      (2, 4, 30f)
+    ).toDF("user", "item", "rating")
+
+    val actual = dataset
+      .select("user", "item")
+      .as[(Int, Int)]
+      .groupByKey(_._1)
+      .mapGroups { case (src, ids) => (src, ids.map(_._2).toArray) }
+      .toDF("id", "actual")
+
+    dataset.join(actual, dataset("user") === actual("id")).collect()
+  }
 }
 
 case class OtherTuple(_1: String, _2: Int)