[SPARK-3197] [SQL] Reduce the Expression tree object creations for aggregation function (min/max)

Aggregation function min/max in catalyst will create expression tree for each single row, however, the expression tree creation is quite expensive in a multithreading env currently. Hence we got a very bad performance for the min/max.
Here is the benchmark that I've done in my local.

Master | Previous Result (ms) | Current Result (ms)
------------ | ------------- | -------------
local | 3645 | 3416
local[6] | 3602 | 1002

The Benchmark source code.
```
case class Record(key: Int, value: Int)

object TestHive2 extends HiveContext(new SparkContext("local[6]", "TestSQLContext", new SparkConf()))

object DataPrepare extends App {
  import TestHive2._

  val rdd = sparkContext.parallelize((1 to 10000000).map(i => Record(i % 3000, i)), 12)

  runSqlHive("SHOW TABLES")
  runSqlHive("DROP TABLE if exists a")
  runSqlHive("DROP TABLE if exists result")
  rdd.registerAsTable("records")

  runSqlHive("""CREATE TABLE a (key INT, value INT)
                 | ROW FORMAT SERDE
                 | 'org.apache.hadoop.hive.serde2.columnar.LazyBinaryColumnarSerDe'
                 | STORED AS RCFILE
               """.stripMargin)
  runSqlHive("""CREATE TABLE result (key INT, value INT)
                 | ROW FORMAT SERDE
                 | 'org.apache.hadoop.hive.serde2.columnar.LazyBinaryColumnarSerDe'
                 | STORED AS RCFILE
               """.stripMargin)

  hql(s"""from records
             | insert into table a
             | select key, value
           """.stripMargin)
}

object PerformanceTest extends App {
  import TestHive2._

  hql("SHOW TABLES")
  hql("set spark.sql.shuffle.partitions=12")

  val cmd = "select min(value), max(value) from a group by key"

  val results = ("Result1", benchmark(cmd)) ::
                ("Result2", benchmark(cmd)) ::
                ("Result3", benchmark(cmd)) :: Nil
  results.foreach { case (prompt, result) => {
      println(s"$prompt: took ${result._1} ms (${result._2} records)")
    }
  }

  def benchmark(cmd: String) = {
    val begin = System.currentTimeMillis()
    val count = hql(cmd).count
    val end = System.currentTimeMillis()
    ((end - begin), count)
  }
}
```

Author: Cheng Hao <hao.cheng@intel.com>

Closes #2113 from chenghao-intel/aggregation_expression_optimization and squashes the following commits:

db40395 [Cheng Hao] remove the transient and add val for the expression property
d56167d [Cheng Hao] Reduce the Expressions creation

2 files changed, 18 insertions, 17 deletions

diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregates.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregates.scala
index dbc0c2965a..15560a2a93 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregates.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregates.scala
@@ -105,17 +105,18 @@ case class Min(child: Expression) extends PartialAggregate with trees.UnaryNode[
 case class MinFunction(expr: Expression, base: AggregateExpression) extends AggregateFunction {
   def this() = this(null, null) // Required for serialization.
 
-  var currentMin: Any = _
+  val currentMin: MutableLiteral = MutableLiteral(null, expr.dataType)
+  val cmp = GreaterThan(currentMin, expr)
 
   override def update(input: Row): Unit = {
-    if (currentMin == null) {
-      currentMin = expr.eval(input)
-    } else if(GreaterThan(Literal(currentMin, expr.dataType), expr).eval(input) == true) {
-      currentMin = expr.eval(input)
+    if (currentMin.value == null) {
+      currentMin.value = expr.eval(input)
+    } else if(cmp.eval(input) == true) {
+      currentMin.value = expr.eval(input)
     }
   }
 
-  override def eval(input: Row): Any = currentMin
+  override def eval(input: Row): Any = currentMin.value
 }
 
 case class Max(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
@@ -135,17 +136,18 @@ case class Max(child: Expression) extends PartialAggregate with trees.UnaryNode[
 case class MaxFunction(expr: Expression, base: AggregateExpression) extends AggregateFunction {
   def this() = this(null, null) // Required for serialization.
 
-  var currentMax: Any = _
+  val currentMax: MutableLiteral = MutableLiteral(null, expr.dataType)
+  val cmp = LessThan(currentMax, expr)
 
   override def update(input: Row): Unit = {
-    if (currentMax == null) {
-      currentMax = expr.eval(input)
-    } else if(LessThan(Literal(currentMax, expr.dataType), expr).eval(input) == true) {
-      currentMax = expr.eval(input)
+    if (currentMax.value == null) {
+      currentMax.value = expr.eval(input)
+    } else if(cmp.eval(input) == true) {
+      currentMax.value = expr.eval(input)
     }
   }
 
-  override def eval(input: Row): Any = currentMax
+  override def eval(input: Row): Any = currentMax.value
 }
 
 case class Count(child: Expression) extends PartialAggregate with trees.UnaryNode[Expression] {
@@ -350,7 +352,7 @@ case class AverageFunction(expr: Expression, base: AggregateExpression)
   private val zero = Cast(Literal(0), expr.dataType)
 
   private var count: Long = _
-  private val sum = MutableLiteral(zero.eval(EmptyRow))
+  private val sum = MutableLiteral(zero.eval(null), expr.dataType)
   private val sumAsDouble = Cast(sum, DoubleType)
 
   private def addFunction(value: Any) = Add(sum, Literal(value))
@@ -423,7 +425,7 @@ case class SumFunction(expr: Expression, base: AggregateExpression) extends Aggr
 
   private val zero = Cast(Literal(0), expr.dataType)
 
-  private val sum = MutableLiteral(zero.eval(null))
+  private val sum = MutableLiteral(zero.eval(null), expr.dataType)
 
   private val addFunction = Add(sum, Coalesce(Seq(expr, zero)))
 
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/literals.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/literals.scala
index a8c2396d62..78a0c55e4b 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/literals.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/literals.scala
@@ -61,11 +61,10 @@ case class Literal(value: Any, dataType: DataType) extends LeafExpression {
 }
 
 // TODO: Specialize
-case class MutableLiteral(var value: Any, nullable: Boolean = true) extends LeafExpression {
+case class MutableLiteral(var value: Any, dataType: DataType, nullable: Boolean = true) 
+    extends LeafExpression {
   type EvaluatedType = Any
 
-  val dataType = Literal(value).dataType
-
   def update(expression: Expression, input: Row) = {
     value = expression.eval(input)
   }