[SPARK-16135][SQL] Remove hashCode and euqals in ArrayBasedMapData

## What changes were proposed in this pull request?
This pr is to remove `hashCode` and `equals` in `ArrayBasedMapData` because the type cannot be used as join keys, grouping keys, or in equality tests.

## How was this patch tested?
Add a new test suite `MapDataSuite` for comparison tests.

Author: Takeshi YAMAMURO <linguin.m.s@gmail.com>

Closes #13847 from maropu/UnsafeMapTest.

(cherry picked from commit 3e4e868)
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/UnsafeArrayData.java

@@ -298,6 +298,10 @@ public UnsafeMapData getMap(int ordinal) {
     return map;
   }
 
+  // This `hashCode` computation could consume much processor time for large data.
+  // If the computation becomes a bottleneck, we can use a light-weight logic; the first fixed bytes
+  // are used to compute `hashCode` (See `Vector.hashCode`).
+  // The same issue exists in `UnsafeRow.hashCode`.
   @Override
   public int hashCode() {
     return Murmur3_x86_32.hashUnsafeBytes(baseObject, baseOffset, sizeInBytes, 42);

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/ArrayBasedMapData.scala

@@ -24,23 +24,6 @@ class ArrayBasedMapData(val keyArray: ArrayData, val valueArray: ArrayData) exte
 
   override def copy(): MapData = new ArrayBasedMapData(keyArray.copy(), valueArray.copy())
 
-  override def equals(o: Any): Boolean = {
-    if (!o.isInstanceOf[ArrayBasedMapData]) {
-      return false
-    }
-
-    val other = o.asInstanceOf[ArrayBasedMapData]
-    if (other eq null) {
-      return false
-    }
-
-    this.keyArray == other.keyArray && this.valueArray == other.valueArray
-  }
-
-  override def hashCode: Int = {
-    keyArray.hashCode() * 37 + valueArray.hashCode()
-  }
-
   override def toString: String = {
     s"keys: $keyArray, values: $valueArray"
   }

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/MapData.scala

@@ -19,6 +19,11 @@ package org.apache.spark.sql.catalyst.util
 
 import org.apache.spark.sql.types.DataType
 
+/**
+ * This is an internal data representation for map type in Spark SQL. This should not implement
+ * `equals` and `hashCode` because the type cannot be used as join keys, grouping keys, or
+ * in equality tests. See SPARK-9415 and PR#13847 for the discussions.
+ */
 abstract class MapData extends Serializable {
 
   def numElements(): Int

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/CodeGenerationSuite.scala

@@ -110,10 +110,10 @@ class CodeGenerationSuite extends SparkFunSuite with ExpressionEvalHelper {
         case (expr, i) => Seq(Literal(i), expr)
       }))
     val plan = GenerateMutableProjection.generate(expressions)
-    val actual = plan(new GenericMutableRow(length)).toSeq(expressions.map(_.dataType))
-    val expected = Seq(new ArrayBasedMapData(
-      new GenericArrayData(0 until length),
-      new GenericArrayData(Seq.fill(length)(true))))
+    val actual = plan(new GenericMutableRow(length)).toSeq(expressions.map(_.dataType)).map {
+      case m: ArrayBasedMapData => ArrayBasedMapData.toScalaMap(m)
+    }
+    val expected = (0 until length).map((_, true)).toMap :: Nil
 
     if (!checkResult(actual, expected)) {
       fail(s"Incorrect Evaluation: expressions: $expressions, actual: $actual, expected: $expected")

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvalHelper.scala

@@ -26,6 +26,7 @@ import org.apache.spark.sql.catalyst.{CatalystTypeConverters, InternalRow}
 import org.apache.spark.sql.catalyst.expressions.codegen._
 import org.apache.spark.sql.catalyst.optimizer.SimpleTestOptimizer
 import org.apache.spark.sql.catalyst.plans.logical.{OneRowRelation, Project}
+import org.apache.spark.sql.catalyst.util.MapData
 import org.apache.spark.sql.types.DataType
 import org.apache.spark.util.Utils
 
@@ -52,15 +53,18 @@ trait ExpressionEvalHelper extends GeneratorDrivenPropertyChecks {
 
   /**
    * Check the equality between result of expression and expected value, it will handle
-   * Array[Byte] and Spread[Double].
+   * Array[Byte], Spread[Double], and MapData.
    */
   protected def checkResult(result: Any, expected: Any): Boolean = {
     (result, expected) match {
       case (result: Array[Byte], expected: Array[Byte]) =>
         java.util.Arrays.equals(result, expected)
       case (result: Double, expected: Spread[Double @unchecked]) =>
         expected.asInstanceOf[Spread[Double]].isWithin(result)
-      case _ => result == expected
+      case (result: MapData, expected: MapData) =>
+        result.keyArray() == expected.keyArray() && result.valueArray() == expected.valueArray()
+      case _ =>
+        result == expected
     }
   }
 

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/MapDataSuite.scala

@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.expressions
+
+import scala.collection._
+
+import org.apache.spark.SparkFunSuite
+import org.apache.spark.sql.catalyst.util.ArrayBasedMapData
+import org.apache.spark.sql.types.{DataType, IntegerType, MapType, StringType}
+import org.apache.spark.unsafe.types.UTF8String
+
+class MapDataSuite extends SparkFunSuite {
+
+  test("inequality tests") {
+    def u(str: String): UTF8String = UTF8String.fromString(str)
+
+    // test data
+    val testMap1 = Map(u("key1") -> 1)
+    val testMap2 = Map(u("key1") -> 1, u("key2") -> 2)
+    val testMap3 = Map(u("key1") -> 1)
+    val testMap4 = Map(u("key1") -> 1, u("key2") -> 2)
+
+    // ArrayBasedMapData
+    val testArrayMap1 = ArrayBasedMapData(testMap1.toMap)
+    val testArrayMap2 = ArrayBasedMapData(testMap2.toMap)
+    val testArrayMap3 = ArrayBasedMapData(testMap3.toMap)
+    val testArrayMap4 = ArrayBasedMapData(testMap4.toMap)
+    assert(testArrayMap1 !== testArrayMap3)
+    assert(testArrayMap2 !== testArrayMap4)
+
+    // UnsafeMapData
+    val unsafeConverter = UnsafeProjection.create(Array[DataType](MapType(StringType, IntegerType)))
+    val row = new GenericMutableRow(1)
+    def toUnsafeMap(map: ArrayBasedMapData): UnsafeMapData = {
+      row.update(0, map)
+      val unsafeRow = unsafeConverter.apply(row)
+      unsafeRow.getMap(0).copy
+    }
+    assert(toUnsafeMap(testArrayMap1) !== toUnsafeMap(testArrayMap3))
+    assert(toUnsafeMap(testArrayMap2) !== toUnsafeMap(testArrayMap4))
+  }
+}